1
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Bai Q, Xuan S, Li W, Ali K, Zheng B, Ren H. Molecular mechanism of brassinosteroids involved in root gravity response based on transcriptome analysis. BMC PLANT BIOLOGY 2024; 24:485. [PMID: 38822229 PMCID: PMC11143716 DOI: 10.1186/s12870-024-05174-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2023] [Accepted: 05/20/2024] [Indexed: 06/02/2024]
Abstract
BACKGROUND Brassinosteroids (BRs) are a class of phytohormones that regulate a wide range of developmental processes in plants. BR-associated mutants display impaired growth and response to developmental and environmental stimuli. RESULTS Here, we found that a BR-deficient mutant det2-1 displayed abnormal root gravitropic growth in Arabidopsis, which was not present in other BR mutants. To further elucidate the role of DET2 in gravity, we performed transcriptome sequencing and analysis of det2-1 and bri1-116, bri1 null mutant allele. Expression levels of auxin, gibberellin, cytokinin, and other related genes in the two mutants of det2-1 and bri1-116 were basically the same. However, we only found that a large number of JAZ (JASMONATE ZIM-domain) genes and jasmonate synthesis-related genes were upregulated in det2-1 mutant, suggesting increased levels of endogenous JA. CONCLUSIONS Our results also suggested that DET2 not only plays a role in BR synthesis but may also be involved in JA regulation. Our study provides a new insight into the molecular mechanism of BRs on the root gravitropism.
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Affiliation(s)
- Qunwei Bai
- College of Life Sciences, Shaanxi Normal University, Xi'an, Shaanxi Province, 710119, PR China
- Shaanxi Key Laboratory of Chinese Jujube, College of Life Sciences, Yan'an University, Yan'an, Shaanxi Province, 716000, PR China
| | - Shurong Xuan
- College of Life Sciences, Shaanxi Normal University, Xi'an, Shaanxi Province, 710119, PR China
| | - Wenjuan Li
- College of Life Sciences, Shaanxi Normal University, Xi'an, Shaanxi Province, 710119, PR China
| | - Khawar Ali
- College of Life Sciences, Shaanxi Normal University, Xi'an, Shaanxi Province, 710119, PR China
| | - Bowen Zheng
- College of Life Sciences, Shaanxi Normal University, Xi'an, Shaanxi Province, 710119, PR China
| | - Hongyan Ren
- College of Life Sciences, Shaanxi Normal University, Xi'an, Shaanxi Province, 710119, PR China.
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2
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Voothuluru P, Wu Y, Sharp RE. Not so hidden anymore: Advances and challenges in understanding root growth under water deficits. THE PLANT CELL 2024; 36:1377-1409. [PMID: 38382086 PMCID: PMC11062450 DOI: 10.1093/plcell/koae055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 02/09/2024] [Accepted: 02/15/2024] [Indexed: 02/23/2024]
Abstract
Limited water availability is a major environmental factor constraining plant development and crop yields. One of the prominent adaptations of plants to water deficits is the maintenance of root growth that enables sustained access to soil water. Despite early recognition of the adaptive significance of root growth maintenance under water deficits, progress in understanding has been hampered by the inherent complexity of root systems and their interactions with the soil environment. We highlight selected milestones in the understanding of root growth responses to water deficits, with emphasis on founding studies that have shaped current knowledge and set the stage for further investigation. We revisit the concept of integrated biophysical and metabolic regulation of plant growth and use this framework to review central growth-regulatory processes occurring within root growth zones under water stress at subcellular to organ scales. Key topics include the primary processes of modifications of cell wall-yielding properties and osmotic adjustment, as well as regulatory roles of abscisic acid and its interactions with other hormones. We include consideration of long-recognized responses for which detailed mechanistic understanding has been elusive until recently, for example hydrotropism, and identify gaps in knowledge, ongoing challenges, and opportunities for future research.
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Affiliation(s)
- Priya Voothuluru
- Division of Plant Science and Technology, University of Missouri, Columbia, MO 65211, USA
- Interdisciplinary Plant Group, University of Missouri, Columbia, MO 65211, USA
| | - Yajun Wu
- Department of Biology and Microbiology, South Dakota State University, Brookings, SD 57007, USA
| | - Robert E Sharp
- Division of Plant Science and Technology, University of Missouri, Columbia, MO 65211, USA
- Interdisciplinary Plant Group, University of Missouri, Columbia, MO 65211, USA
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3
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Pang L, Kobayashi A, Atsumi Y, Miyazawa Y, Fujii N, Dietrich D, Bennett MJ, Takahashi H. MIZU-KUSSEI1 (MIZ1) and GNOM/MIZ2 control not only positive hydrotropism but also phototropism in Arabidopsis roots. JOURNAL OF EXPERIMENTAL BOTANY 2023; 74:5026-5038. [PMID: 37220914 DOI: 10.1093/jxb/erad193] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Accepted: 05/22/2023] [Indexed: 05/25/2023]
Abstract
In response to unilateral blue light illumination, roots of some plant species such as Arabidopsis thaliana exhibit negative phototropism (bending away from light), which is important for light avoidance in nature. MIZU-KUSSEI1 (MIZ1) and GNOM/MIZ2 are essential for positive hydrotropism (i.e. in the presence of a moisture gradient, root bending towards greater water availability). Intriguingly, mutations in these genes also cause a substantial reduction in phototropism. Here, we examined whether the same tissue-specific sites of expression required for MIZ1- and GNOM/MIZ2-regulated hydrotropism in Arabidopsis roots are also required for phototropism. The attenuated phototropic response of miz1 roots was completely restored when a functional MIZ1-green fluorescent protein (GFP) fusion was expressed in the cortex of the root elongation zone but not in other tissues such as root cap, meristem, epidermis, or endodermis. The hydrotropic defect and reduced phototropism of miz2 roots were restored by GNOM/MIZ2 expression in either the epidermis, cortex, or stele, but not in the root cap or endodermis. Thus, the sites in root tissues that are involved in the regulation of MIZ1- and GNOM/MIZ2-dependent hydrotropism also regulate phototropism. These results suggest that MIZ1- and GNOM/MIZ2-mediated pathways are, at least in part, shared by hydrotropic and phototropic responses in Arabidopsis roots.
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Affiliation(s)
- Lei Pang
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Akie Kobayashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Yuka Atsumi
- Graduate School of Science and Engineering, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
| | - Yutaka Miyazawa
- Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Daniela Dietrich
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Plant and Crop Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Malcolm J Bennett
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Plant and Crop Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
- Research Center for Space Agriculture and Horticulture, Graduate School of Horticulture, Chiba University, 648 Matsudo, Chiba 271-8510, Japan
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4
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Akita K, Miyazawa Y. Auxin biosynthesis, transport, and response directly attenuate hydrotropism in the latter stages to fine-tune root growth direction in Arabidopsis. PHYSIOLOGIA PLANTARUM 2023; 175:e14051. [PMID: 37882259 DOI: 10.1111/ppl.14051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 09/28/2023] [Accepted: 10/05/2023] [Indexed: 10/27/2023]
Abstract
Roots detect water potential gradients in the soil and orient toward moister areas, a response known as hydrotropism that aids drought avoidance. Although auxin is crucial in tropism, its polar transport is not essential for hydrotropism in Arabidopsis. Moreover, antiauxin treatments in Arabidopsis produced inconsistent outcomes: some studies indicated auxin action was necessary while others did not. In this study, we examined auxin's physiological role in hydrotropism. We found that inhibiting auxin biosynthesis or transport intensified hydrotropic bending not only in wild-type, but also in hydrotropism defective mutants, namely miz1-1 and miz2 plants. Given that miz1-1 and miz2 exhibited compromised hydrotropism even under clinorotated conditions, we infer that auxin biosynthesis and transport directly suppress hydrotropism. Additionally, tir1-10, afb1-3, and afb2-3 displayed augmented hydrotropism. We observed a significant delay in hydrotropic bending in arf7-1arf19-1, suggesting that ARF7 and ARF19 amplify hydrotropism in its early stages. To discern the functional ties of ARF7/19 with MIZ1 and MIZ2, we studied the hydrotropic phenotypes of arf7-1arf19-1miz1-1 and arf7-1arf19-1miz2. Both triple mutants had diminished early-stage hydrotropism yet showed partial but significant recovery in the later stages. Given MIZ1's role in reducing auxin levels and MIZ2's essentiality for MIZ1 functionality, we conclude that auxin inhibits hydrotropism downstream of MIZ1 in later stages to refine root bending. Furthermore, it is posited that gene expression driven by ARF7 and ARF19 is pivotal for early-stage root hydrotropism.
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Affiliation(s)
- Kotaro Akita
- Graduate School of Science and Engineering, Yamagata University, Yamagata, Japan
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5
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Tarkowski ŁP, Signorelli S, Considine MJ, Montrichard F. Integration of reactive oxygen species and nutrient signalling to shape root system architecture. PLANT, CELL & ENVIRONMENT 2023; 46:379-390. [PMID: 36479711 PMCID: PMC10107350 DOI: 10.1111/pce.14504] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 11/30/2022] [Accepted: 12/05/2022] [Indexed: 06/17/2023]
Abstract
Yield losses due to nutrient deficiency are estimated as the primary cause of the yield gap worldwide. Understanding how plant roots perceive external nutrient status and elaborate morphological adaptations in response to it is necessary to develop reliable strategies to increase crop yield. In the last decade, reactive oxygen species (ROS) were shown to be key players of the mechanisms underlying root responses to nutrient limitation. ROS contribute in multiple ways to shape the root system in response to nutritional cues, both as direct effectors acting on cell wall architecture and as second messengers in signalling pathways. Here, we review the mutual interconnections existing between perception and signalling of the most common forms of the major macronutrients (nitrogen, phosphorus and potassium), and ROS in shaping plant root system architecture. We discuss recent advances in dissecting the integration of these elements and their impact on morphological traits of the root system, highlighting the functional ductility of ROS and enzymes implied in ROS metabolism, such as class III peroxidases.
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Affiliation(s)
| | - Santiago Signorelli
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Molecular SciencesUniversity of Western AustraliaPerthWestern AustraliaAustralia
- Food and Plant Biology group, Departamento de Biología Vegetal, Facultad de AgronomíaUniversidad de la RepúblicaMontevideoUruguay
| | - Michael J. Considine
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Molecular SciencesUniversity of Western AustraliaPerthWestern AustraliaAustralia
- Department of Primary Industries and Regional DevelopmentPerthWestern AustraliaAustralia
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6
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Wang CY, Li LL, Meiners SJ, Kong CH. Root placement patterns in allelopathic plant-plant interactions. THE NEW PHYTOLOGIST 2023; 237:563-575. [PMID: 36263726 DOI: 10.1111/nph.18552] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Accepted: 10/07/2022] [Indexed: 06/16/2023]
Abstract
Plants actively respond to their neighbors by altering root placement patterns. Neighbor-modulated root responses involve root detection and interactions mediated by root-secreted functional metabolites. However, chemically mediated root placement patterns and their underlying mechanisms remain elusive. We used an allelopathic wheat model system challenged with 60 target species to identify root placement responses in window rhizobox experiments. We then tested root responses and their biochemical mechanisms in incubation experiments involving the addition of activated carbon and functional metabolites with amyloplast staining and auxin localization in roots. Wheat and each target species demonstrated intrusive, avoidant or unresponsive root placement, resulting in a total of nine combined patterns. Root placement patterns were mediated by wheat allelochemicals and (-)-loliolide signaling of neighbor species. In particular, (-)-loliolide triggered wheat allelochemical production that altered root growth and placement, degraded starch grains in the root cap and induced uneven distribution of auxin in target species roots. Root placement patterns in wheat-neighbor interactions were perception dependent and species dependent. Signaling (-)-loliolide induced the production and release of wheat allelochemicals that modulated root placement patterns. Therefore, root placement patterns are generated by both signaling chemicals and allelochemicals in allelopathic plant-plant interactions.
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Affiliation(s)
- Chao-Yong Wang
- College of Resources and Environmental Sciences, China Agricultural University, Beijing, 100193, China
| | - Lei-Lei Li
- College of Resources and Environmental Sciences, China Agricultural University, Beijing, 100193, China
| | - Scott J Meiners
- Department of Biological Sciences, Eastern Illinois University, Charleston, IL, 61920, USA
| | - Chui-Hua Kong
- College of Resources and Environmental Sciences, China Agricultural University, Beijing, 100193, China
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7
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Mao B, Takahashi H, Takahashi H, Fujii N. Diversity of root hydrotropism among natural variants of Arabidopsis thaliana. JOURNAL OF PLANT RESEARCH 2022; 135:799-808. [PMID: 36149514 PMCID: PMC10039817 DOI: 10.1007/s10265-022-01412-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 09/08/2022] [Indexed: 05/30/2023]
Abstract
Root gravitropism affects root hydrotropism. The interference intensity of root gravitropism with root hydrotropism differs among plant species. However, these differences have not been well compared within a single plant species. In this study, we compared root hydrotropism in various natural variants of Arabidopsis under stationary conditions. As a result, we detected a range of root hydrotropism under stationary conditions among natural Arabidopsis variants. Comparison of root gravitropism and root hydrotropism among several Arabidopsis natural variants classified natural variants that decreased root hydrotropism into two types; namely one type that expresses root gravitropism and root hydrotropism weaker than Col-0, and the other type that expresses weaker root hydrotropism than Col-0 but expresses similar root gravitropism with Col-0. However, root hydrotropism of all examined Arabidopsis natural variants was facilitated by clinorotation. These results suggested that the interference of root gravitropism with root hydrotropism is conserved among Arabidopsis natural variants, although the intensity of root gravitropism interference with root hydrotropism differs.
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Affiliation(s)
- Boyuan Mao
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai, 980-8577, Japan
| | - Hiroki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai, 980-8577, Japan
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai, 980-8577, Japan
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai, 980-8577, Japan.
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8
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Yamazaki K, Fujiwara T. The Effect of Phosphate on the Activity and Sensitivity of Nutritropism toward Ammonium in Rice Roots. PLANTS (BASEL, SWITZERLAND) 2022; 11:733. [PMID: 35336615 PMCID: PMC8955032 DOI: 10.3390/plants11060733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Revised: 03/07/2022] [Accepted: 03/07/2022] [Indexed: 11/16/2022]
Abstract
Understanding how plants determine growth direction from environmental cues is important to reveal optimal strategies in plant survival. Nutritropism is the directional growth of plant roots towards nutrient sources. Our previous study showed that an NH4+ gradient stimulates nutritropism in the lateral roots, but not in the main roots, of a rice cultivar. In the present study, we report nutritropism in the main roots of rice accessions among the World Rice Core Collection, including WRC 25. We investigated the effects of components in nutrient sources on nutritropism in WRC 25. Nutritropism in main roots was stimulated by NH4+ and significantly enhanced by Pi. We found that roots required more NH4+ stimulation for nutritropic responses in the presence of higher Pi, meaning that Pi desensitized root nutritropism. These results indicate that Pi acts as an activator and a desensitizer in nutritropism. Such a regulation of nutritropism would be important for plants to decide their optimum growth directions towards nutrient sources, gravity, moisture, or other stimuli.
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Affiliation(s)
- Kiyoshi Yamazaki
- Graduate School of Agricultural and Life Science, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan;
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9
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Zhu JD, Wang J, Guo XN, Shang BS, Yan HR, Zhang X, Zhao X. A high concentration of abscisic acid inhibits hypocotyl phototropism in Gossypium arboreum by reducing accumulation and asymmetric distribution of auxin. JOURNAL OF EXPERIMENTAL BOTANY 2021; 72:6365-6381. [PMID: 34145440 DOI: 10.1093/jxb/erab298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Accepted: 06/16/2021] [Indexed: 06/12/2023]
Abstract
Hypocotyl phototropism is mediated by the phototropins and plays a critical role in seedling morphogenesis by optimizing growth orientation. However, the mechanisms by which phototropism influences morphogenesis require additional study, especially for polyploid crops such as cotton. Here, we found that hypocotyl phototropism was weaker in Gossypium arboreum than in G. raimondii (two diploid cotton species), and LC-MS analysis indicated that G. arboreum hypocotyls had a higher content of abscisic acid (ABA) and a lower content of indole-3-acetic acid (IAA) and bioactive gibberellins (GAs). Consistently, the expression of ABA2, AAO3, and GA2OX1 was higher in G. arboreum than in G. raimondii, and that of GA3OX was lower; these changes promoted ABA synthesis and the transformation of active GA to inactive GA. Higher concentrations of ABA inhibited the asymmetric distribution of IAA across the hypocotyl and blocked the phototropic curvature of G. raimondii. Application of IAA or GA3 to the shaded and illuminated sides of the hypocotyl enhanced and inhibited phototropic curvature, respectively, in G. arboreum. The application of IAA, but not GA, to one side of the hypocotyl caused hypocotyl curvature in the dark. These results indicate that the asymmetric distribution of IAA promotes phototropic growth, and the weakened phototropic curvature of G. arboreum may be attributed to its higher ABA concentrations that inhibit the action of auxin, which is regulated by GA signaling.
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Affiliation(s)
- Jin-Dong Zhu
- Key laboratory of plant stress biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng, China
| | - Jing Wang
- Key laboratory of plant stress biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng, China
| | - Xi-Ning Guo
- Key laboratory of plant stress biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng, China
| | - Bao-Shuan Shang
- Key laboratory of plant stress biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng, China
| | - Hong-Ru Yan
- Key laboratory of plant stress biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng, China
| | - Xiao Zhang
- Key laboratory of plant stress biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng, China
| | - Xiang Zhao
- Key laboratory of plant stress biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng, China
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10
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Li Y, Yuan W, Li L, Dai H, Dang X, Miao R, Baluška F, Kronzucker HJ, Lu C, Zhang J, Xu W. Comparative analysis reveals gravity is involved in the MIZ1-regulated root hydrotropism. JOURNAL OF EXPERIMENTAL BOTANY 2020; 71:7316-7330. [PMID: 32905588 DOI: 10.1093/jxb/eraa409] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 09/07/2020] [Indexed: 06/11/2023]
Abstract
Hydrotropism is the directed growth of roots toward the water found in the soil. However, mechanisms governing interactions between hydrotropism and gravitropism remain largely unclear. In this study, we found that an air system and an agar-sorbitol system induced only oblique water-potential gradients; an agar-glycerol system induced only vertical water-potential gradients; and a sand system established both oblique and vertical water-potential gradients. We employed obliquely oriented and vertically oriented experimental systems to study hydrotropism in Arabidopsis and tomato plants. Comparative analyses using different hydrotropic systems showed that gravity hindered the ability of roots to search for obliquely oriented water, whilst facilitating roots' search for vertically oriented water. We found that the gravitropism-deficient mutant aux1 showed enhanced hydrotropism in the oblique orientation but impaired root elongation towards water in the vertical orientation. The miz1 mutant exhibited deficient hydrotropism in the oblique orientation but normal root elongation towards water in the vertical orientation. Importantly, in contrast to miz1, the miz1/aux1 double mutant exhibited hydrotropic bending in the oblique orientation and attenuated root elongation towards water in the vertical orientation. Our results suggest that gravitropism is required for MIZ1-regulated root hydrotropism in both the oblique orientation and the vertical orientation, providing further insight into the role of gravity in root hydrotropism.
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Affiliation(s)
- Ying Li
- Center for Plant Water-use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and college of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou, China
| | - Wei Yuan
- Center for Plant Water-use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and college of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou, China
| | - Luocheng Li
- Center for Plant Water-use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and college of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou, China
| | - Hui Dai
- Center for Plant Water-use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and college of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou, China
| | - Xiaolin Dang
- Center for Plant Water-use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and college of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou, China
| | - Rui Miao
- Center for Plant Water-use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and college of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou, China
| | - František Baluška
- Institute of Cellular and Molecular Botany, University of Bonn, Bonn, Germany
| | - Herbert J Kronzucker
- School of Agriculture and Food, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, VIC, Australia
- Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada
| | - Congming Lu
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Taian, Shandong, China
| | - Jianhua Zhang
- Department of Biology, Hong Kong Baptist University, Stake Key Laboratory of Agrobiotechnology and Chinese University of Hong Kong, Hong Kong
| | - Weifeng Xu
- Center for Plant Water-use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and college of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou, China
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11
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Li Y, Yuan W, Li L, Miao R, Dai H, Zhang J, Xu W. Light-Dark Modulates Root Hydrotropism Associated with Gravitropism by Involving Amyloplast Response in Arabidopsis. Cell Rep 2020; 32:108198. [PMID: 32997985 DOI: 10.1016/j.celrep.2020.108198] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Revised: 07/28/2020] [Accepted: 09/03/2020] [Indexed: 12/13/2022] Open
Abstract
The role of amyloplasts in the interactions between hydrotropism and gravitropism has been previously described. However, the effect of light-dark on the interactions between the two tropisms remains unclear. Here, by developing a method that makes it possible to mimic natural conditions more closely than the conventional lab conditions, we show that hydrotropism is higher in wild-type Arabidopsis seedlings whose shoots are illuminated but whose roots are grown in the dark compared with seedlings that are fully exposed to light. Root gravitropism is substantially decreased because of the reduction of amyloplast content in the root tip with decreased gene expression in PGM1 (a key starch biosynthesis gene), which may contribute to enhanced root hydrotropism under darkness. Furthermore, the starch-deficient mutant pgm1-1 exhibits greater hydrotropism compared with wild-type. Our results suggest that amyloplast response and starch reduction occur under light-dark modulation, followed by decreased gravitropism and enhanced hydrotropism in Arabidopsis root.
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Affiliation(s)
- Ying Li
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and College of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China
| | - Wei Yuan
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and College of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China
| | - Luocheng Li
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and College of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China
| | - Rui Miao
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and College of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China
| | - Hui Dai
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and College of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China
| | - Jianhua Zhang
- Department of Biology, Hong Kong Baptist University, Hong Kong, China
| | - Weifeng Xu
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop and College of Resource and Environment, Fujian Agriculture and Forestry University, Jinshan, Fuzhou 350002, China.
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12
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Yamazaki K, Ohmori Y, Fujiwara T. A Positive Tropism of Rice Roots toward a Nutrient Source. PLANT & CELL PHYSIOLOGY 2020; 61:546-553. [PMID: 31808938 DOI: 10.1093/pcp/pcz218] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 11/22/2019] [Indexed: 06/10/2023]
Abstract
Plants take up water and nutrients through roots, and uptake efficiency depends on root behavior. Roots recognize the moisture gradient in the soil and grow toward the direction of high moisture. This phenomenon is called hydrotropism, and it contributes to efficient water uptake. As nutrients in soil are also unevenly distributed, it is beneficial for plants to grow their roots in the direction of increasing nutrient concentrations, but such a phenomenon has not been demonstrated. Here, we describe the directional growth of roots in response to a nutrient gradient. Using our assay system, the gradient of a nitrogen nutrient, NH4+, was sufficient to stimulate positive tropic responses of rice lateral roots. This phenomenon is a tropism of plant roots to nutrients; hence, we propose the name 'nutritropism'. As well as other tropisms, differential cell elongation was observed before the elongation zone during nutritropism, but the pattern promoting cell elongation preferentially on the non-stimulated side was opposite to those in root hydrotropism and gravitropism. Our evaluation of the NH4+ gradient suggested that the root tips responded to a sub-micromolar difference in NH4+ concentration on both sides of the root. Hydrotropism, gravitropism and phototropism were described in plants as the 'power of movement' by Charles and Francis Darwin in 1880, and these three tropisms have attracted the attention of plant scientists for more than 130 years. Our discovery of nutritropism represents the fourth 'power of movement' in plants and provides a novel root behavioral property used by plants to acquire nutrients efficiently.
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Affiliation(s)
- Kiyoshi Yamazaki
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-8657 Japan
| | - Yoshihiro Ohmori
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-8657 Japan
- Agricultural Bioinformatics Research Unit, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-8657 Japan
| | - Toru Fujiwara
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-8657 Japan
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13
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Kaur V, Yadav SK, Wankhede DP, Pulivendula P, Kumar A, Chinnusamy V. Cloning and characterization of a gene encoding MIZ1, a domain of unknown function protein and its role in salt and drought stress in rice. PROTOPLASMA 2020; 257:475-487. [PMID: 31786672 DOI: 10.1007/s00709-019-01452-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2019] [Accepted: 10/22/2019] [Indexed: 05/19/2023]
Abstract
Dwindling fresh water resources and climate change poses serious threats to rice production. Roots play crucial role in sensing water gradient and directing growth of the plant towards water through a mechanism called hydrotropism. Since very little information is available on root hydrotropism in major food crops, this study was carried out to clone and characterize an ortholog of Arabidopsis MIZU-KUSSEI1 (MIZ1) from rice. Contrasting rice genotypes for drought and salt tolerance were selected based on phenotyping for root traits. Nagina 22 and CR-262-4 were identified as most tolerant and Pusa Sugandh 5 and Pusa Basmati 1121 were identified as most susceptible varieties for both drought and salt stresses. Allele mining of MIZ1 in these varieties identified a 12 bp Indel but did not show specific allelic association with stress tolerance. Analysis of allelic variation of OsMIZ1 in 3024 rice genotypes of 3K genome lines using Rice SNP-Seek database revealed 49 InDels. Alleles with the 12 bp deletions were significantly prevalent in indica group as compared to that of japonica group. Real-time RT-PCR analysis revealed that OsMIZ1 expression levels were upregulated significantly in tolerant cv. Nagina 22 and CR-262-4 under osmotic stress, while under salt stress, it was significantly upregulated only in CR-262-4 but maintained in Nagina 22 under salt stress. However, in the roots of susceptible genotypes, OsMIZ1 expression decreased under both the stresses. These results highlight the possible involvement of OsMIZ1 in drought and salt stress tolerance in rice. Furthermore, expression studies using publically available resources showed that enhanced expression of OsMIZ1 is regulated in response to disease infections, mineral deficiency, and heavy metal stresses and is also expressed in reproductive tissues in addition to roots. These findings indicate potential involvement of MIZ1 in developmental and stress response processes in rice.
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Affiliation(s)
- Vikender Kaur
- ICAR-National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi, 110012, India.
| | - Shashank K Yadav
- Division of Plant Physiology, ICAR-Indian Agricultural Research Institute, Pusa Campus, New Delhi, 110012, India
| | | | - Pranusha Pulivendula
- ICAR-National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi, 110012, India
| | - Ashok Kumar
- ICAR-National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi, 110012, India
| | - Viswanathan Chinnusamy
- Division of Plant Physiology, ICAR-Indian Agricultural Research Institute, Pusa Campus, New Delhi, 110012, India.
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14
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Lee HJ, Kim HS, Park JM, Cho HS, Jeon JH. PIN-mediated polar auxin transport facilitates root-obstacle avoidance. THE NEW PHYTOLOGIST 2020; 225:1285-1296. [PMID: 31336402 DOI: 10.1111/nph.16076] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 07/18/2019] [Indexed: 05/20/2023]
Abstract
Plants sense mechanical stimuli to recognise nearby obstacles and change their growth patterns to adapt to the surrounding environment. When roots encounter an obstacle, they rapidly bend away from the impenetrable surface and find the edge of the barrier. However, the molecular mechanisms underlying root-obstacle avoidance are largely unknown. Here, we demonstrate that PIN-FORMED (PIN)-mediated polar auxin transport facilitates root bending during obstacle avoidance. We analysed two types of bending after roots touched barriers. In auxin receptor mutants, the rate of root movement during first bending was largely delayed. Gravity-oriented second bending was also disturbed in these mutants. The reporter assays showed that asymmetrical auxin responses occurred in the roots during obstacle avoidance. Pharmacological analysis suggested that polar auxin transport mediates local auxin accumulation. We found that PINs are required for auxin-assisted root bending during obstacle avoidance. We propose that rapid root movement during obstacle avoidance is not just a passive but an active bending completed through polar auxin transport. Our findings suggest that auxin plays a role in thigmotropism during plant-obstacle interactions.
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Affiliation(s)
- Hyo-Jun Lee
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, 34141, Korea
- Department of Functional Genomics, KRIBB School of Bioscience, University of Science and Technology, Daejeon, 34113, Korea
| | - Hyun-Soon Kim
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, 34141, Korea
| | - Jeong Mee Park
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, 34141, Korea
- Department of Biosystems and Bioengineering, KRIBB School of Biotechnology, University of Science and Technology, Daejeon, 34113, Korea
| | - Hye Sun Cho
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, 34141, Korea
- Department of Biosystems and Bioengineering, KRIBB School of Biotechnology, University of Science and Technology, Daejeon, 34113, Korea
| | - Jae Heung Jeon
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, 34141, Korea
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15
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Miyazawa Y, Takahashi H. Molecular mechanisms mediating root hydrotropism: what we have observed since the rediscovery of hydrotropism. JOURNAL OF PLANT RESEARCH 2020; 133:3-14. [PMID: 31797131 PMCID: PMC7082378 DOI: 10.1007/s10265-019-01153-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Accepted: 11/19/2019] [Indexed: 06/02/2023]
Abstract
Roots display directional growth toward moisture in response to a water potential gradient. Root hydrotropism is thought to facilitate plant adaptation to continuously changing water availability. Hydrotropism has not been as extensively studied as gravitropism. However, comparisons of hydrotropic and gravitropic responses identified mechanisms that are unique to hydrotropism. Regulatory mechanisms underlying the hydrotropic response appear to differ among different species. We recently performed molecular and genetic analyses of root hydrotropism in Arabidopsis thaliana. In this review, we summarize the current knowledge of specific mechanisms mediating root hydrotropism in several plant species.
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Affiliation(s)
- Yutaka Miyazawa
- Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata, 990-8560, Japan.
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
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16
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Lehman TA, Sanguinet KA. Auxin and Cell Wall Crosstalk as Revealed by the Arabidopsis thaliana Cellulose Synthase Mutant Radially Swollen 1. PLANT & CELL PHYSIOLOGY 2019; 60:1487-1503. [PMID: 31004494 DOI: 10.1093/pcp/pcz055] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Accepted: 03/29/2019] [Indexed: 06/09/2023]
Abstract
Plant cells sheath themselves in a complex lattice of polysaccharides, proteins and enzymes forming an integral matrix known as the cell wall. Cellulose microfibrils, the primary component of cell walls, are synthesized at the plasma membrane by CELLULOSE SYNTHASE A (CESA) proteins throughout cellular growth and are responsible for turgor-driven anisotropic expansion. Associations between hormone signaling and cell wall biosynthesis have long been suggested, but recently direct links have been found revealing hormones play key regulatory roles in cellulose biosynthesis. The radially swollen 1 (rsw1) allele of Arabidopsis thaliana CESA1 harbors a single amino acid change that renders the protein unstable at high temperatures. We used the conditional nature of rsw1 to investigate how auxin contributes to isotropic growth. We found that exogenous auxin treatment reduces isotropic swelling in rsw1 roots at the restrictive temperature of 30�C. We also discovered decreases in auxin influx between rsw1 and wild-type roots via confocal imaging of AUX1-YFP, even at the permissive temperature of 19�C. Moreover, rsw1 displayed mis-expression of auxin-responsive and CESA genes. Additionally, we found altered auxin maxima in rsw1 mutant roots at the onset of swelling using DII-VENUS and DR5:vYFP auxin reporters. Overall, we conclude disrupted cell wall biosynthesis perturbs auxin transport leading to altered auxin homeostasis impacting both anisotropic and isotropic growth that affects overall root morphology.
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Affiliation(s)
- Thiel A Lehman
- Department of Crop and Soil Sciences, Washington State University, Pullman, WA, USA
| | - Karen A Sanguinet
- Department of Crop and Soil Sciences, Washington State University, Pullman, WA, USA
- Molecular Plant Sciences Graduate Group, Washington State University, Pullman, WA, USA
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17
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Tanaka-Takada N, Kobayashi A, Takahashi H, Kamiya T, Kinoshita T, Maeshima M. Plasma Membrane-Associated Ca2+-Binding Protein PCaP1 is Involved in Root Hydrotropism of Arabidopsis thaliana. PLANT & CELL PHYSIOLOGY 2019; 60:1331-1341. [PMID: 30828737 DOI: 10.1093/pcp/pcz042] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Accepted: 02/21/2019] [Indexed: 05/26/2023]
Abstract
Root hydrotropism is an essential growth response to water potential gradients in plants. To understand the mechanism, fundamental elements such as MIZU-KUSSEI 1 (MIZ1) have been investigated extensively. We investigated the physiological role of a plasma membrane-associated cation-binding protein (PCaP1) and examined the effect of PCaP1 loss-of-function mutations on root hydrotropism. pcap1 knockout mutants showed a defect in root bending as a hydrotropic response, although gravitropism was normal in pcap1 mutants. When pcap1 seedlings were treated with abscisic acid, a negative regulator of gravitropism, the seedlings showed normal gravitropism. The hydrotropism defect in pcap1 mutants was clearly rescued by introducing the genomic sequence of PCaP1 with an endodermis-specific promoter. Analysis of PCaP1-greenfluorescent protein-expressing roots by confocal laser scanning microscopy revealed that PCaP1 was stably associated with the plasma membrane in most cells, but in the cytoplasm of endodermal cells at the bending region. Furthermore, we prepared a transgenic line overexpressing MIZ1 on the pcap1 background and found that the pcap1 hydrotropism defect was rescued. Our results indicate that PCaP1 in the endodermal cells of the root elongation zone is involved in the hydrotropic response. We suggest that PCaP1 contributes to hydrotropism through a MIZ1-independent pathway or as one of the upstream components that transduce water potential signals to MIZ1.
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Affiliation(s)
- Natsuki Tanaka-Takada
- Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
- Institute for Advanced Research, Nagoya University, Nagoya, Japan
| | - Akie Kobayashi
- Laboratory of Plant Sennsory and Developmental Biology, Graduate School of Life Sciences, Tohoku University, Sendai, Japan
| | - Hideyuki Takahashi
- Laboratory of Plant Sennsory and Developmental Biology, Graduate School of Life Sciences, Tohoku University, Sendai, Japan
| | - Takehiro Kamiya
- Laboratory of Plant Nutrition and Fertilizers, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan
| | - Toshinori Kinoshita
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya, Japan
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya, Japan
| | - Masayoshi Maeshima
- Laboratory of Cell Dynamics, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
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18
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Muthert LWF, Izzo LG, van Zanten M, Aronne G. Root Tropisms: Investigations on Earth and in Space to Unravel Plant Growth Direction. FRONTIERS IN PLANT SCIENCE 2019; 10:1807. [PMID: 32153599 PMCID: PMC7047216 DOI: 10.3389/fpls.2019.01807] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 12/24/2019] [Indexed: 05/12/2023]
Abstract
Root tropisms are important responses of plants, allowing them to adapt their growth direction. Research on plant tropisms is indispensable for future space programs that envisage plant-based life support systems for long-term missions and planet colonization. Root tropisms encompass responses toward or away from different environmental stimuli, with an underexplored level of mechanistic divergence. Research into signaling events that coordinate tropistic responses is complicated by the consistent coincidence of various environmental stimuli, often interacting via shared signaling mechanisms. On Earth the major determinant of root growth direction is the gravitational vector, acting through gravitropism and overruling most other tropistic responses to environmental stimuli. Critical advancements in the understanding of root tropisms have been achieved nullifying the gravitropic dominance with experiments performed in the microgravity environment. In this review, we summarize current knowledge on root tropisms to different environmental stimuli. We highlight that the term tropism must be used with care, because it can be easily confused with a change in root growth direction due to asymmetrical damage to the root, as can occur in apparent chemotropism, electrotropism, and magnetotropism. Clearly, the use of Arabidopsis thaliana as a model for tropism research contributed much to our understanding of the underlying regulatory processes and signaling events. However, pronounced differences in tropisms exist among species, and we argue that these should be further investigated to get a more comprehensive view of the signaling pathways and sensors. Finally, we point out that the Cholodny-Went theory of asymmetric auxin distribution remains to be the central and unifying tropistic mechanism after 100 years. Nevertheless, it becomes increasingly clear that the theory is not applicable to all root tropistic responses, and we propose further research to unravel commonalities and differences in the molecular and physiological processes orchestrating root tropisms.
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Affiliation(s)
| | - Luigi Gennaro Izzo
- Department of Agricultural Sciences, University of Naples Federico II, Naples, Italy
- *Correspondence: Luigi Gennaro Izzo,
| | - Martijn van Zanten
- Molecular Plant Physiology, Institute of Environmental Biology, Utrecht University, Utrecht, Netherlands
| | - Giovanna Aronne
- Department of Agricultural Sciences, University of Naples Federico II, Naples, Italy
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19
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Dietrich D. Hydrotropism: how roots search for water. JOURNAL OF EXPERIMENTAL BOTANY 2018; 69:2759-2771. [PMID: 29529239 DOI: 10.1093/jxb/ery034] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 01/18/2018] [Indexed: 05/25/2023]
Abstract
Fresh water is an increasingly scarce resource for agriculture. Plant roots mediate water uptake from the soil and have developed a number of adaptive traits such as hydrotropism to aid water foraging. Hydrotropism modifies root growth to respond to a water potential gradient in soil and grow towards areas with a higher moisture content. Abscisic acid (ABA) and a small number of genes, including those encoding ABA signal transducers, MIZ2/GNOM, and the hydrotropism-specific MIZ1, are known to be necessary for the response in Arabidopsis thaliana, whereas the role of auxin in hydrotropism appears to vary depending on the plant species. This review will describe recent progress characterizing the hormonal regulation of hydrotropism. Recent advances in identifying the sites of hydrotropic perception and response, together with its interaction with gravitropism, will also be discussed. Finally, I will describe putative mechanisms for perception of the water potential gradient and a potential role for hydrotropism in acclimatizing plants to drought conditions.
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Affiliation(s)
- Daniela Dietrich
- Centre for Plant Integrative Biology and Plant & Crop Sciences, School of Biosciences, University of Nottingham, Nottingham, UK
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20
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Root-tip-mediated inhibition of hydrotropism is accompanied with the suppression of asymmetric expression of auxin-inducible genes in response to moisture gradients in cucumber roots. PLoS One 2018; 13:e0189827. [PMID: 29324818 PMCID: PMC5764274 DOI: 10.1371/journal.pone.0189827] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 12/01/2017] [Indexed: 11/23/2022] Open
Abstract
In cucumber seedlings, gravitropism interferes with hydrotropism, which results in the nearly complete inhibition of hydrotropism under stationary conditions. However, hydrotropic responses are induced when the gravitropic response in the root is nullified by clinorotation. Columella cells in the root cap sense gravity, which induces the gravitropic response. In this study, we found that removing the root tip induced hydrotropism in cucumber roots under stationary conditions. The application of auxin transport inhibitors to cucumber seedlings under stationary conditions suppressed the hydrotropic response induced by the removal of the root tip. To investigate the expression of genes related to hydrotropism in de-tipped cucumber roots, we conducted transcriptome analysis of gene expression by RNA-Seq using seedlings exhibiting hydrotropic and gravitropic responses. Of the 21 and 45 genes asymmetrically expressed during hydrotropic and gravitropic responses, respectively, five genes were identical. Gene ontology (GO) analysis indicated that the category auxin-inducible genes was significantly enriched among genes that were more highly expressed in the concave side of the root than the convex side during hydrotropic or gravitropic responses. Reverse transcription followed by quantitative polymerase chain reaction (RT-qPCR) analysis revealed that root hydrotropism induced under stationary conditions (by removing the root tip) was accompanied by the asymmetric expression of several auxin-inducible genes. However, intact roots did not exhibit the asymmetric expression patterns of auxin-inducible genes under stationary conditions, even in the presence of a moisture gradient. These results suggest that the root tip inhibits hydrotropism by suppressing the induction of asymmetric auxin distribution. Auxin transport and distribution not mediated by the root tip might play a role in hydrotropism in cucumber roots.
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21
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Iqbal A, Wang T, Wu G, Tang W, Zhu C, Wang D, Li Y, Wang H. Physiological and transcriptome analysis of heteromorphic leaves and hydrophilic roots in response to soil drying in desert Populus euphratica. Sci Rep 2017; 7:12188. [PMID: 28939837 PMCID: PMC5610244 DOI: 10.1038/s41598-017-12091-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Accepted: 09/04/2017] [Indexed: 01/08/2023] Open
Abstract
Populus euphratica Olivier, which has been considered as a tree model for the study of higher plant response to abiotic stresses, survive in the desert ecosystem characterized by extreme drought stress. To survive in the harsh environmental condition the plant species have developed some plasticity such as the development of heteromorphic leaves and well-developed roots system. We investigated the physiological and molecular mechanisms enabling this species to cope with severe stress caused by drought. The heterophylly, evolved from linear to toothed-ovate shape, showed the significant difference in cuticle thickness, stomata densities, and sizes. Physiological parameters, SOD, POD, PPO, CAT activity, free proline, soluble protein and MDA contents fluctuated in response to soil drying. Gene expression profile of roots monitored at control and 4 moisture gradients regimes showed the up-regulation of 124, 130, 126 and 162 and down-regulation of 138, 251, 314, 168 DEGs, respectively. Xyloglucan endotransglucosylase/ hydrolase gene (XET) up-regulated at different moisture gradients, was cloned and expressed in tobacco. The XET promoter sequence harbors the drought signaling responsive cis-elements. The promoter expression activity varies in different organs. Over-expression and knocked down transgenic tobacco plant analysis confirmed the role of XET gene in roots growth and drought resistance.
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Affiliation(s)
- Arshad Iqbal
- College of Biological Sciences and Biotechnology, National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, 100083, China
| | - Tianxiang Wang
- College of Biological Sciences and Biotechnology, National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, 100083, China
| | - Guodong Wu
- College of Biological Sciences and Biotechnology, National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, 100083, China
| | - Wensi Tang
- College of Biological Sciences and Biotechnology, National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, 100083, China
| | - Chen Zhu
- College of Biological Sciences and Biotechnology, National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, 100083, China
| | - Dapeng Wang
- College of Biological Sciences and Biotechnology, National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, 100083, China
| | - Yi Li
- Department of Plant Science, University of Connecticut, Storrs, CT, 06269, USA
| | - Huafang Wang
- College of Biological Sciences and Biotechnology, National Engineering Laboratory for Tree Breeding, Beijing Forestry University, Beijing, 100083, China.
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Morohashi K, Okamoto M, Yamazaki C, Fujii N, Miyazawa Y, Kamada M, Kasahara H, Osada I, Shimazu T, Fusejima Y, Higashibata A, Yamazaki T, Ishioka N, Kobayashi A, Takahashi H. Gravitropism interferes with hydrotropism via counteracting auxin dynamics in cucumber roots: clinorotation and spaceflight experiments. THE NEW PHYTOLOGIST 2017; 215:1476-1489. [PMID: 28722158 DOI: 10.1111/nph.14689] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 05/28/2017] [Indexed: 05/27/2023]
Abstract
Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation. Gravitropism interferes with hydrotropism, although the mechanistic aspects are poorly understood. Here, we differentiated hydrotropism from gravitropism in cucumber roots by conducting clinorotation and spaceflight experiments. We also compared mechanisms regulating hydrotropism and auxin-regulated gravitropism. Clinorotated or microgravity (μG)-grown cucumber seedling roots hydrotropically bent toward wet substrate in the presence of moisture gradients, but they grew straight in the direction of normal gravitational force at the Earth's surface (1G) on the ground or centrifuge-generated 1G in space. The roots appeared to become hydrotropically more sensitive to moisture gradients under μG conditions in space. Auxin transport inhibitors significantly reduced the hydrotropic response of clinorotated seedling roots. The auxin efflux protein CsPIN5 was differentially expressed in roots of both clinorotated and μG-grown seedlings; with higher expression in the high-humidity (concave) side than the low-humidity (convex) side of hydrotropically responding roots. Our results suggest that roots become hydrotropically sensitive in μG, and CsPIN5-mediated auxin transport has an important role in inducing root hydrotropism. Thus, hydrotropic and gravitropic responses in cucumber roots may compete via differential auxin dynamics established in response to moisture gradients and gravity.
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Affiliation(s)
- Keita Morohashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
| | - Miki Okamoto
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
| | - Chiaki Yamazaki
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
- Japan Space Forum, 3-2-1 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-0062, Japan
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
| | - Yutaka Miyazawa
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
- Faculty of Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata, 990-8560, Japan
| | - Motoshi Kamada
- Advanced Engineering Services Co. Ltd, 1-6-1 Takezono, Tsukuba, 305-0032, Japan
| | - Haruo Kasahara
- Japan Manned Space Systems Co., 1-6-1 Otemachi, Chiyoda-ku, Tokyo, 100-0004, Japan
| | - Ikuko Osada
- Japan Manned Space Systems Co., 1-6-1 Otemachi, Chiyoda-ku, Tokyo, 100-0004, Japan
| | - Toru Shimazu
- Japan Space Forum, 3-2-1 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-0062, Japan
| | - Yasuo Fusejima
- Japan Space Forum, 3-2-1 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-0062, Japan
| | - Akira Higashibata
- JEM Utilization Center, Japan Aerospace Exploration Agency, 2-1-1 Sengen, Tsukuba, 305-8505, Japan
| | - Takashi Yamazaki
- Graduate School of Medicine, Teikyo University, 2-11-1 Kaga, Itabashi-ku, Tokyo, 173-8605, Japan
| | - Noriaki Ishioka
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, 252-5210, Japan
| | - Akie Kobayashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
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23
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Nakajima Y, Nara Y, Kobayashi A, Sugita T, Miyazawa Y, Fujii N, Takahashi H. Auxin transport and response requirements for root hydrotropism differ between plant species. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:3441-3456. [PMID: 28633373 DOI: 10.1093/jxb/erx193] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2023]
Abstract
The direction of auxin transport changes in gravistimulated roots, causing auxin accumulation in the lower side of horizontally reoriented roots. This study found that auxin was similarly involved in hydrotropism and gravitropism in rice and pea roots, but hydrotropism in Lotus japonicus roots was independent of both auxin transport and response. Application of either auxin transport inhibitors or an auxin response inhibitor decreased both hydrotropism and gravitropism in rice roots, and reduced hydrotropism in pea roots. However, Lotus roots treated with these inhibitors showed reduced gravitropism but an unaltered or an enhanced hydrotropic response. Inhibiting auxin biosynthesis substantially reduced both tropisms in rice and Lotus roots. Removing the final 0.2 mm (including the root cap) from the root tip inhibited gravitropism but not hydrotropism in rice seedling roots. These results suggested that modes of auxin involvement in hydrotropism differed between plant species. In rice roots, although auxin transport and responses were required for both gravitropism and hydrotropism, the root cap was involved in the auxin regulation of gravitropism but not hydrotropism. Hydrotropism in Lotus roots, however, may be regulated by a novel mechanism that is independent of both auxin transport and the TIR1/AFBs auxin response pathway.
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Affiliation(s)
- Yusuke Nakajima
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Yoshitaka Nara
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Akie Kobayashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Tomoki Sugita
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Yutaka Miyazawa
- Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
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24
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Dietrich D, Pang L, Kobayashi A, Fozard JA, Boudolf V, Bhosale R, Antoni R, Nguyen T, Hiratsuka S, Fujii N, Miyazawa Y, Bae TW, Wells DM, Owen MR, Band LR, Dyson RJ, Jensen OE, King JR, Tracy SR, Sturrock CJ, Mooney SJ, Roberts JA, Bhalerao RP, Dinneny JR, Rodriguez PL, Nagatani A, Hosokawa Y, Baskin TI, Pridmore TP, De Veylder L, Takahashi H, Bennett MJ. Root hydrotropism is controlled via a cortex-specific growth mechanism. NATURE PLANTS 2017; 3:17057. [PMID: 28481327 DOI: 10.1038/nplants.2017.57] [Citation(s) in RCA: 134] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 03/23/2017] [Indexed: 05/24/2023]
Abstract
Plants can acclimate by using tropisms to link the direction of growth to environmental conditions. Hydrotropism allows roots to forage for water, a process known to depend on abscisic acid (ABA) but whose molecular and cellular basis remains unclear. Here we show that hydrotropism still occurs in roots after laser ablation removed the meristem and root cap. Additionally, targeted expression studies reveal that hydrotropism depends on the ABA signalling kinase SnRK2.2 and the hydrotropism-specific MIZ1, both acting specifically in elongation zone cortical cells. Conversely, hydrotropism, but not gravitropism, is inhibited by preventing differential cell-length increases in the cortex, but not in other cell types. We conclude that root tropic responses to gravity and water are driven by distinct tissue-based mechanisms. In addition, unlike its role in root gravitropism, the elongation zone performs a dual function during a hydrotropic response, both sensing a water potential gradient and subsequently undergoing differential growth.
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Affiliation(s)
- Daniela Dietrich
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Plant &Crop Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Lei Pang
- Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan
| | - Akie Kobayashi
- Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan
| | - John A Fozard
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
| | - Véronique Boudolf
- Department of Plant Biotechnology and Bioinformatics, Ghent University, (Technologiepark 927), 9052 Ghent, Belgium
- VIB Center for Plant Systems Biology, (Technologiepark 927), 9052 Ghent, Belgium
| | - Rahul Bhosale
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Plant &Crop Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
- Department of Plant Biotechnology and Bioinformatics, Ghent University, (Technologiepark 927), 9052 Ghent, Belgium
- VIB Center for Plant Systems Biology, (Technologiepark 927), 9052 Ghent, Belgium
| | - Regina Antoni
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
| | - Tuan Nguyen
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- School of Computer Science, University of Nottingham, Nottingham NG8 1BB, UK
| | - Sotaro Hiratsuka
- Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan
| | - Yutaka Miyazawa
- Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
| | - Tae-Woong Bae
- Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan
| | - Darren M Wells
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Plant &Crop Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Markus R Owen
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Centre for Mathematical Medicine &Biology, University of Nottingham, Nottingham NG7 2RD, UK
| | - Leah R Band
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Centre for Mathematical Medicine &Biology, University of Nottingham, Nottingham NG7 2RD, UK
| | - Rosemary J Dyson
- School of Mathematics, University of Birmingham, Birmingham B15 2TT, UK
| | - Oliver E Jensen
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- School of Mathematics, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - John R King
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Centre for Mathematical Medicine &Biology, University of Nottingham, Nottingham NG7 2RD, UK
| | - Saoirse R Tracy
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Craig J Sturrock
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Sacha J Mooney
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Jeremy A Roberts
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Plant &Crop Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Rishikesh P Bhalerao
- Department of Forest Genetics and Plant Physiology, SLU, S-901 83 Umea, Sweden
- College of Science, KSU, Riyadh, Saudi Arabia
| | - José R Dinneny
- Department of Plant Biology, Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA
| | - Pedro L Rodriguez
- Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Cientificas-Universidad Politecnica de Valencia, ES-46022 Valencia, Spain
| | - Akira Nagatani
- Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Yoichiroh Hosokawa
- Graduate School of Materials Science, Nara Institute of Science &Technology, Ikoma 630-0101, Japan
| | - Tobias I Baskin
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Biology Department, University of Massachusetts, Amherst, Massachusetts 01003-9297, USA
| | - Tony P Pridmore
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- School of Computer Science, University of Nottingham, Nottingham NG8 1BB, UK
| | - Lieven De Veylder
- Department of Plant Biotechnology and Bioinformatics, Ghent University, (Technologiepark 927), 9052 Ghent, Belgium
- VIB Center for Plant Systems Biology, (Technologiepark 927), 9052 Ghent, Belgium
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan
| | - Malcolm J Bennett
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
- Plant &Crop Sciences, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
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25
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Zhu R, Dong X, Hao W, Gao W, Zhang W, Xia S, Liu T, Shang Z. Heterotrimeric G Protein-Regulated Ca 2+ Influx and PIN2 Asymmetric Distribution Are Involved in Arabidopsis thaliana Roots' Avoidance Response to Extracellular ATP. FRONTIERS IN PLANT SCIENCE 2017; 8:1522. [PMID: 28919907 PMCID: PMC5585194 DOI: 10.3389/fpls.2017.01522] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Accepted: 08/18/2017] [Indexed: 05/04/2023]
Abstract
Extracellular ATP (eATP) has been reported to be involved in plant growth as a primary messenger in the apoplast. Here, roots of Arabidopsis thaliana seedlings growing in jointed medium bent upon contact with ATP-containing medium to keep away from eATP, showing a marked avoidance response. Roots responded similarly to ADP and bz-ATP but did not respond to AMP and GTP. The eATP avoidance response was reduced in loss-of-function mutants of heterotrimeric G protein α subunit (Gα) (gpa1-1 and gpa1-2) and enhanced in Gα-over-expression (OE) lines (wGα and cGα). Ethylenebis(oxyethylenenitrilo) tetraacetic acid (EGTA) and Gd3+ remarkably suppressed eATP-induced root bending. ATP-stimulated Ca2+ influx was impaired in Gα null mutants and increased in its OE lines. DR5-GFP and PIN2 were asymmetrically distributed in ATP-stimulated root tips, this effect was strongly suppressed by EGTA and diminished in Gα null mutants. In addition, some eATP-induced genes' expression was also impaired in Gα null mutants. Based on these results, we propose that heterotrimeric Gα-regulated Ca2+ influx and PIN2 distribution may be key signaling events in eATP sensing and avoidance response in Arabidopsis thaliana roots.
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26
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Shkolnik D, Fromm H. The Cholodny-Went theory does not explain hydrotropism. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2016; 252:400-403. [PMID: 27717476 DOI: 10.1016/j.plantsci.2016.09.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Revised: 09/10/2016] [Accepted: 09/12/2016] [Indexed: 05/11/2023]
Abstract
Optimization of water foraging by plants is partially achieved by the ability of roots to direct growth towards high water potential, a phenomenon termed hydrotropism. In contrast to gravitropism and phototropism, which require auxin redistribution, as suggested by the Cholodny-Went theory, hydrotropism is not mediated by the phytohormone auxin, which raises questions about the mechanism underlying this tropic response. Here we specify the open questions in this field of research and discuss the possible interactions of abscisic acid, calcium and reactive oxygen species as part of a dynamic system of sensing water potential in the root tip, transmission of the signal to the root elongation zone and promoting root curvature towards water. We conclude that root hydrotropism is mediated by inter-cellular signals that are not explained by the Cholodny-Went theory.
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Affiliation(s)
- Doron Shkolnik
- Department of Molecular Biology & Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 69978 Israel
| | - Hillel Fromm
- Department of Molecular Biology & Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 69978 Israel.
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27
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Koevoets IT, Venema JH, Elzenga JTM, Testerink C. Roots Withstanding their Environment: Exploiting Root System Architecture Responses to Abiotic Stress to Improve Crop Tolerance. FRONTIERS IN PLANT SCIENCE 2016; 7:1335. [PMID: 27630659 PMCID: PMC5005332 DOI: 10.3389/fpls.2016.01335] [Citation(s) in RCA: 194] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 08/18/2016] [Indexed: 05/18/2023]
Abstract
To face future challenges in crop production dictated by global climate changes, breeders and plant researchers collaborate to develop productive crops that are able to withstand a wide range of biotic and abiotic stresses. However, crop selection is often focused on shoot performance alone, as observation of root properties is more complex and asks for artificial and extensive phenotyping platforms. In addition, most root research focuses on development, while a direct link to the functionality of plasticity in root development for tolerance is often lacking. In this paper we review the currently known root system architecture (RSA) responses in Arabidopsis and a number of crop species to a range of abiotic stresses, including nutrient limitation, drought, salinity, flooding, and extreme temperatures. For each of these stresses, the key molecular and cellular mechanisms underlying the RSA response are highlighted. To explore the relevance for crop selection, we especially review and discuss studies linking root architectural responses to stress tolerance. This will provide a first step toward understanding the relevance of adaptive root development for a plant's response to its environment. We suggest that functional evidence on the role of root plasticity will support breeders in their efforts to include root properties in their current selection pipeline for abiotic stress tolerance, aimed to improve the robustness of crops.
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Affiliation(s)
- Iko T. Koevoets
- Swammerdam Institute for Life Sciences, Plant Cell Biology, University of AmsterdamAmsterdam, Netherlands
| | - Jan Henk Venema
- Genomics Research in Ecology and Evolution in Nature – Plant Physiology, Groningen Institute for Evolutionary Life Sciences, University of GroningenGroningen, Netherlands
| | - J. Theo. M. Elzenga
- Genomics Research in Ecology and Evolution in Nature – Plant Physiology, Groningen Institute for Evolutionary Life Sciences, University of GroningenGroningen, Netherlands
| | - Christa Testerink
- Swammerdam Institute for Life Sciences, Plant Cell Biology, University of AmsterdamAmsterdam, Netherlands
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28
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Kim HJ, Kobayashi A, Fujii N, Miyazawa Y, Takahashi H. Gravitropic response and circumnutation in pea (Pisum sativum) seedling roots. PHYSIOLOGIA PLANTARUM 2016; 157:108-18. [PMID: 26565659 DOI: 10.1111/ppl.12406] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Revised: 10/03/2015] [Accepted: 10/05/2015] [Indexed: 06/05/2023]
Abstract
Plant circumnutation is a helical movement of growing organs such as shoots and roots. Gravitropic response is hypothesized to act as an external oscillator in shoot circumnutation, although this is subject to debate. The relationship between circumnutational movement and gravitropic response in roots remains unknown. In this study, we analyzed circumnutation of agravitropic roots using the ageotropum pea (Pisum sativum) mutant, and compared it with that of wild-type (cv. Alaska) pea roots. We further examined the relationship of gravitropic response to circumnutation of Alaska seedling roots by removing the gravisensing tissue (the root cap) and by treating the roots with auxin transport inhibitors. Alaska roots displayed circumnutational movements with a period of approximately 150 min, whereas ageotropum roots did not exhibit distinct circumnutational movement. Removal of the root cap in Alaska roots reduced gravitropic response and circumnutational movements. Treatment of Alaska roots with auxin transport inhibitors, 2,3,5-triiodobenzoic acid (TIBA) and N-(1-naphthyl)phthalamic acid (NPA), dramatically reduced gravitropic response and circumnutational movements. These results suggest that a gravity-regulated auxin transport is involved in circumnutation of pea seedling roots.
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Affiliation(s)
- Hye-jeong Kim
- Graduate School of Life Sciences, Tohoku University, Sendai, 980-8577, Japan
| | - Akie Kobayashi
- Graduate School of Life Sciences, Tohoku University, Sendai, 980-8577, Japan
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, Sendai, 980-8577, Japan
| | - Yutaka Miyazawa
- Department of Biology, Faculty of Science, Yamagata University, Yamagata, 990-8560, Japan
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, Sendai, 980-8577, Japan
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29
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Slovak R, Ogura T, Satbhai SB, Ristova D, Busch W. Genetic control of root growth: from genes to networks. ANNALS OF BOTANY 2016; 117:9-24. [PMID: 26558398 PMCID: PMC4701154 DOI: 10.1093/aob/mcv160] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Accepted: 08/28/2015] [Indexed: 05/08/2023]
Abstract
BACKGROUND Roots are essential organs for higher plants. They provide the plant with nutrients and water, anchor the plant in the soil, and can serve as energy storage organs. One remarkable feature of roots is that they are able to adjust their growth to changing environments. This adjustment is possible through mechanisms that modulate a diverse set of root traits such as growth rate, diameter, growth direction and lateral root formation. The basis of these traits and their modulation are at the cellular level, where a multitude of genes and gene networks precisely regulate development in time and space and tune it to environmental conditions. SCOPE This review first describes the root system and then presents fundamental work that has shed light on the basic regulatory principles of root growth and development. It then considers emerging complexities and how they have been addressed using systems-biology approaches, and then describes and argues for a systems-genetics approach. For reasons of simplicity and conciseness, this review is mostly limited to work from the model plant Arabidopsis thaliana, in which much of the research in root growth regulation at the molecular level has been conducted. CONCLUSIONS While forward genetic approaches have identified key regulators and genetic pathways, systems-biology approaches have been successful in shedding light on complex biological processes, for instance molecular mechanisms involving the quantitative interaction of several molecular components, or the interaction of large numbers of genes. However, there are significant limitations in many of these methods for capturing dynamic processes, as well as relating these processes to genotypic and phenotypic variation. The emerging field of systems genetics promises to overcome some of these limitations by linking genotypes to complex phenotypic and molecular data using approaches from different fields, such as genetics, genomics, systems biology and phenomics.
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Affiliation(s)
- Radka Slovak
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Takehiko Ogura
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Santosh B Satbhai
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Daniela Ristova
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Wolfgang Busch
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
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30
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Affiliation(s)
- Qian Gao
- Dept. of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering; Xiamen University; Xiamen Fujian Province 361005 P.R. China
| | - Jie Xiao
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science; Soochow University; Suzhou Jiangsu Province 215123 P.R. China
| | - Xiao Dong Chen
- Dept. of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering; Xiamen University; Xiamen Fujian Province 361005 P.R. China
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science; Soochow University; Suzhou Jiangsu Province 215123 P.R. China
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31
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Barlow PW. The natural history of consciousness, and the question of whether plants are conscious, in relation to the Hameroff-Penrose quantum-physical 'Orch OR' theory of universal consciousness. Commun Integr Biol 2015; 8:e1041696. [PMID: 26478778 PMCID: PMC4594572 DOI: 10.1080/19420889.2015.1041696] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Revised: 03/28/2015] [Accepted: 04/13/2015] [Indexed: 12/23/2022] Open
Affiliation(s)
- Peter W Barlow
- School of Biological Sciences; University of Bristol; Bristol Life Sciences Building; Bristol, UK
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32
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Gao B, Wen C, Fan L, Kou Y, Ma N, Zhao L. A Rosa canina WUSCHEL-related homeobox gene, RcWOX1, is involved in auxin-induced rhizoid formation. PLANT MOLECULAR BIOLOGY 2014; 86:671-679. [PMID: 25301174 DOI: 10.1007/s11103-014-0255-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Accepted: 10/05/2014] [Indexed: 06/04/2023]
Abstract
Homeobox (HB) proteins are important transcription factors that regulate the developmental decisions of eukaryotes. WUSCHEL-related homeobox (WOX) transcription factors, known as a plant-specific HB family, play a key role in plant developmental processes. Our previous work has indicated that rhizoids are induced by auxin in rose (Rosa spp.), which acts as critical part of an efficient plant regeneration system. However, the function of WOX genes in auxin-induced rhizoid formation remains unclear. Here, we isolated and characterized a WUSCHEL-related homeobox gene from Rosa canina, RcWOX1, containing a typical homeodomain with 65 amino acid residues. Real-time reverse transcription PCR (qRT-PCR) analysis revealed that RcWOX1 was expressed in the whole process of callus formation and in the early stage of rhizoid formation. Moreover, its expression was induced by auxin treatment. In Arabidopsis transgenic lines expressing the RcWOX1pro::GUS and 35S::GFP-RcWOX1, RcWOX1 was specifically expressed in roots and localized to the nucleus. Overexpression of RcWOX1 in Arabidopsis increased lateral root density and induced upregulation of PIN1 and PIN7 genes. Therefore, we postulated that RcWOX1 is a functional transcription factor that plays an essential role in auxin-induced rhizoid formation.
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Affiliation(s)
- Bin Gao
- Department of Ornamental Horticulture and Landscape Architecture, China Agricultural University, Yuanmingyuan West Road, Haidian District, Beijing, 100193, China
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33
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Moriwaki T, Miyazawa Y, Fujii N, Takahashi H. GNOM regulates root hydrotropism and phototropism independently of PIN-mediated auxin transport. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2014; 215-216:141-9. [PMID: 24388525 DOI: 10.1016/j.plantsci.2013.11.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 09/26/2013] [Accepted: 11/04/2013] [Indexed: 05/11/2023]
Abstract
Plant roots exhibit tropisms in response to gravity, unilateral light and moisture gradients. During gravitropism, an auxin gradient is established by PIN auxin transporters, leading to asymmetric growth. GNOM, a guanine nucleotide exchange factor of ARF GTPase (ARF-GEF), regulates PIN localization by regulating subcellular trafficking of PINs. Therefore, GNOM is important for gravitropism. We previously isolated mizu-kussei2 (miz2), which lacks hydrotropic responses; MIZ2 is allelic to GNOM. Since PIN proteins are not required for root hydrotropism in Arabidopsis, the role of GNOM in root hydrotropism should differ from that in gravitropism. To examine this possibility, we conducted genetic analysis of gnom(miz2) and gnom trans-heterozygotes. The mutant gnom(miz2), which lacks hydrotropic responses, was partially recovered by gnom(emb30-1), which lacks GEF activity, but not by gnom(B4049), which lacks heterotypic domain interactions. Furthermore, the phototropic response of gnom trans-heterozygotes differed from that of the pin2 mutant allele eir1-1. Moreover, defects in the polarities of PIN2 and auxin distribution in a severe gnom mutant were recovered by gnom(miz2). Therefore, an unknown GNOM-mediated vesicle trafficking system may mediate root hydrotropism and phototropism independently of PIN trafficking.
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Affiliation(s)
- Teppei Moriwaki
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Yutaka Miyazawa
- Department of Biology, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan.
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
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34
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Ishida H, Izumi M, Wada S, Makino A. Roles of autophagy in chloroplast recycling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1837:512-21. [PMID: 24269172 DOI: 10.1016/j.bbabio.2013.11.009] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Revised: 11/01/2013] [Accepted: 11/07/2013] [Indexed: 01/04/2023]
Abstract
Chloroplasts are the primary energy suppliers for plants, and much of the total leaf nitrogen is distributed to these organelles. During growth and reproduction, chloroplasts in turn represent a major source of nitrogen to be recovered from senescing leaves and used in newly-forming and storage organs. Chloroplast proteins also can be an alternative substrate for respiration under suboptimal conditions. Autophagy is a process of bulk degradation and nutrient sequestration that is conserved in all eukaryotes. Autophagy can selectively target chloroplasts as whole organelles and or as Rubisco-containing bodies that are enclosed by the envelope and specifically contain the stromal portion of the chloroplast. Although information is still limited, recent work indicates that chloroplast recycling via autophagy plays important roles not only in developmental processes but also in organelle quality control and adaptation to changing environments. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.
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Affiliation(s)
- Hiroyuki Ishida
- Graduate School of Agricultural Sciences, Tohoku University, Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan.
| | - Masanori Izumi
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Shinya Wada
- Graduate School of Agricultural Sciences, Tohoku University, Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan
| | - Amane Makino
- Graduate School of Agricultural Sciences, Tohoku University, Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0076, Japan
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Vanneste S, Friml J. Calcium: The Missing Link in Auxin Action. PLANTS (BASEL, SWITZERLAND) 2013; 2:650-75. [PMID: 27137397 PMCID: PMC4844386 DOI: 10.3390/plants2040650] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 10/07/2013] [Accepted: 10/10/2013] [Indexed: 01/18/2023]
Abstract
Due to their sessile lifestyles, plants need to deal with the limitations and stresses imposed by the changing environment. Plants cope with these by a remarkable developmental flexibility, which is embedded in their strategy to survive. Plants can adjust their size, shape and number of organs, bend according to gravity and light, and regenerate tissues that were damaged, utilizing a coordinating, intercellular signal, the plant hormone, auxin. Another versatile signal is the cation, Ca(2+), which is a crucial second messenger for many rapid cellular processes during responses to a wide range of endogenous and environmental signals, such as hormones, light, drought stress and others. Auxin is a good candidate for one of these Ca(2+)-activating signals. However, the role of auxin-induced Ca(2+) signaling is poorly understood. Here, we will provide an overview of possible developmental and physiological roles, as well as mechanisms underlying the interconnection of Ca(2+) and auxin signaling.
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Affiliation(s)
- Steffen Vanneste
- Plant Systems Biology, VIB, and Plant Biotechnology and Bio-informatics, Ghent University, Ghent 9052, Belgium.
| | - Jiří Friml
- Plant Systems Biology, VIB, and Plant Biotechnology and Bio-informatics, Ghent University, Ghent 9052, Belgium
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg 3400, Austria
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Zhang KX, Xu HH, Yuan TT, Zhang L, Lu YT. Blue-light-induced PIN3 polarization for root negative phototropic response in Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2013; 76:308-21. [PMID: 23888933 DOI: 10.1111/tpj.12298] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 06/04/2013] [Accepted: 07/12/2013] [Indexed: 05/04/2023]
Abstract
Root negative phototropism is an important response in plants. Although blue light is known to mediate this response, the cellular and molecular mechanisms underlying root negative phototropism remain unclear. Here, we report that the auxin efflux carrier PIN-FORMED (PIN) 3 is involved in asymmetric auxin distribution and root negative phototropism. Unilateral blue-light illumination polarized PIN3 to the outer lateral membrane of columella cells at the illuminated root side, and increased auxin activity at the illuminated side of roots, where auxin promotes growth and causes roots bending away from the light source. Furthermore, root negative phototropic response and blue-light-induced PIN3 polarization were modulated by a brefeldin A-sensitive, GNOM-dependent, trafficking pathway and by phot1-regulated PINOID (PID)/PROTEIN PHOSPHATASE 2A (PP2A) activity. Our results indicate that blue-light-induced PIN3 polarization is needed for asymmetric auxin distribution during root negative phototropic response.
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Affiliation(s)
- Kun-Xiao Zhang
- Key Lab of MOE for Plant Development, College of Life Sciences, Wuhan University, Wuhan, 430072, China
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37
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Proteomic identification of gravitropic response genes in peanut gynophores. J Proteomics 2013; 93:303-13. [PMID: 23994445 DOI: 10.1016/j.jprot.2013.08.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Revised: 07/11/2013] [Accepted: 08/04/2013] [Indexed: 10/26/2022]
Abstract
UNLABELLED Peanut (Arachis hypogaea L.) is one of the most important oil-bearing crops in the world. The gravitropic response of peanut gynophores plays an essential role in peanut reproductive development. In this study, we developed an in vitro culture system and applied it to the study of peanut gynophore gravitropism. By comparing the proteomes of gynophores grown in vitro with the tip pointing upward (gravity stimulation sample) and downward (natural growth control) at 6h and 12h, we observed 42 and 39 with significantly altered expression pattern at 6 and 12h, respectively. Out of these proteins, 13 proteins showed same expression profiling at both 6h and 12h. They were identified by MALDI-TOF/TOF and further characterized with quantitative real time RT-PCR. Among the 13 identified proteins, two were identified as class III acidic endochitinases, two were identified as Kunitz trypsin protease inhibitors, and the remaining proteins were identified as pathogenesis-related class 10 protein, Ara h 8 allergen isoform 3, voltage-dependent anion channel, gamma carbonic anhydrase 1, germin-like protein subfamily 3 member 3 precursor, chloride channel, glycine-rich RNA-binding protein and gibberellin receptor GID1. Real time RT-PCR analysis revealed that transcriptional regulation is consistent with expression at the protein level for class III acidic endochitinase, Kunitz trypsin protease inhibitor, chloride channel and pathogenesis-related class 10 protein, while the expression of the other 7 proteins might be regulated at post-transcriptional levels. This study identified several potential gravitropic response proteins in peanut gynophores and helps to understand early gravitropic responses in peanut gynophores. BIOLOGICAL SIGNIFICANCE The gravitropic response of the peanut gynophores plays an essential role in peanut production. However, the molecular mechanism responsible for gravitropic responses in the peanut gynophores has not been explored yet. The result generated in this study may provide in vitro culture system for gravitropism study of plant gravitropic response and novel insights into the proteome-level response and give a more comprehensive understanding of early gravitropic response in peanut gynophores. This article is part of a Special Issue entitled: Translational Plant Proteomics.
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Iwata S, Miyazawa Y, Fujii N, Takahashi H. MIZ1-regulated hydrotropism functions in the growth and survival of Arabidopsis thaliana under natural conditions. ANNALS OF BOTANY 2013; 112:103-14. [PMID: 23658369 PMCID: PMC3690989 DOI: 10.1093/aob/mct098] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 03/12/2013] [Indexed: 05/19/2023]
Abstract
BACKGROUND AND AIMS Root hydrotropism is a response to water-potential gradients that makes roots bend towards areas of higher water potential. The gene MIZU-KUSSEI1 (MIZ1) that is essential for hydrotropism in Arabidopsis roots has previously been identified. However, the role of root hydrotropism in plant growth and survival under natural conditions has not yet been proven. This study assessed how hydrotropic response contributes to drought avoidance in nature. METHODS An experimental system was established for the study of Arabidopsis hydrotropism in soil. Characteristics of hydrotropism were analysed by comparing the responses of the miz1 mutant, transgenic plants overexpressing MIZ1 (MIZ1OE) and wild-type plants. KEY RESULTS Wild-type plants developed root systems in regions with higher water potential, whereas the roots of miz1 mutant plants did not show a similar response. This pattern of root distribution induced by hydrotropism was more pronounced in MIZ1OE plants than in wild-type plants. In addition, shoot biomass and the number of plants that survived under drought conditions were much greater in MIZ1OE plants. CONCLUSIONS These results show that hydrotropism plays an important role in root system development in soil and contributes to drought avoidance, which results in a greater yield and plant survival under water-limited conditions. The results also show that MIZ1 overexpression can be used for improving plant productivity in arid areas.
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Affiliation(s)
- Satoru Iwata
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Yutaka Miyazawa
- Department of Biology, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
- For correspondence. E-mail or
| | - Nobuharu Fujii
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Hideyuki Takahashi
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
- For correspondence. E-mail or
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Yu H, Karampelias M, Robert S, Peer WA, Swarup R, Ye S, Ge L, Cohen J, Murphy A, Friml J, Estelle M. ROOT ULTRAVIOLET B-SENSITIVE1/weak auxin response3 is essential for polar auxin transport in Arabidopsis. PLANT PHYSIOLOGY 2013; 162:965-76. [PMID: 23580592 PMCID: PMC3668084 DOI: 10.1104/pp.113.217018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The phytohormone auxin regulates virtually every aspect of plant development. To identify new genes involved in auxin activity, a genetic screen was performed for Arabidopsis (Arabidopsis thaliana) mutants with altered expression of the auxin-responsive reporter DR5rev:GFP. One of the mutants recovered in the screen, designated as weak auxin response3 (wxr3), exhibits much lower DR5rev:GFP expression when treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid and displays severe defects in root development. The wxr3 mutant decreases polar auxin transport and results in a disruption of the asymmetric auxin distribution. The levels of the auxin transporters AUXIN1 and PIN-FORMED are dramatically reduced in the wxr3 root tip. Molecular analyses demonstrate that WXR3 is ROOT ULTRAVIOLET B-SENSITIVE1 (RUS1), a member of the conserved Domain of Unknown Function647 protein family found in diverse eukaryotic organisms. Our data suggest that RUS1/WXR3 plays an essential role in the regulation of polar auxin transport by maintaining the proper level of auxin transporters on the plasma membrane.
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Yu H, Moss BL, Jang SS, Prigge M, Klavins E, Nemhauser JL, Estelle M. Mutations in the TIR1 auxin receptor that increase affinity for auxin/indole-3-acetic acid proteins result in auxin hypersensitivity. PLANT PHYSIOLOGY 2013; 162:295-303. [PMID: 23539280 PMCID: PMC3641209 DOI: 10.1104/pp.113.215582] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The phytohormone auxin regulates virtually every aspect of plant development. The hormone directly mediates the interaction between the two members of the auxin coreceptor complex, a TRANSPORT INHIBITOR RESPONSE (TIR1)/AUXIN SIGNALING F-BOX protein and an AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) transcriptional repressor. To learn more about the interaction between these proteins, a mutant screen was performed using the yeast (Saccharomyces cerevisiae) two-hybrid system in Arabidopsis (Arabidopsis thaliana). Two tir1 mutations were identified that increased interaction with Aux/IAAs. The D170E and M473L mutations increase affinity between TIR1 and the degron motif of Aux/IAAs and enhance the activity of the SCF(TIR1) complex. This resulted in faster degradation of Aux/IAAs and increased transcription of auxin-responsive genes in the plant. Plants carrying the pTIR1:tir1 D170E/M473L-Myc transgene exhibit diverse developmental defects during plant growth and display an auxin-hypersensitive phenotype. This work demonstrates that changes in the leucine-rich repeat domain of the TIR1 auxin coreceptor can alter the properties of SCF(TIR1).
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41
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Schepetilnikov M, Dimitrova M, Mancera-Martínez E, Geldreich A, Keller M, Ryabova LA. TOR and S6K1 promote translation reinitiation of uORF-containing mRNAs via phosphorylation of eIF3h. EMBO J 2013; 32:1087-102. [PMID: 23524850 DOI: 10.1038/emboj.2013.61] [Citation(s) in RCA: 208] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 02/15/2013] [Indexed: 11/09/2022] Open
Abstract
Mammalian target-of-rapamycin (mTOR) triggers S6 kinase (S6K) activation to phosphorylate targets linked to translation in response to energy, nutrients, and hormones. Pathways of TOR activation in plants remain unknown. Here, we uncover the role of the phytohormone auxin in TOR signalling activation and reinitiation after upstream open reading frame (uORF) translation, which in plants is dependent on translation initiation factor eIF3h. We show that auxin triggers TOR activation followed by S6K1 phosphorylation at T449 and efficient loading of uORF-mRNAs onto polysomes in a manner sensitive to the TOR inhibitor Torin-1. Torin-1 mediates recruitment of inactive S6K1 to polysomes, while auxin triggers S6K1 dissociation and recruitment of activated TOR instead. A putative target of TOR/S6K1-eIF3h-is phosphorylated and detected in polysomes in response to auxin. In TOR-deficient plants, polysomes were prebound by inactive S6K1, and loading of uORF-mRNAs and eIF3h was impaired. Transient expression of eIF3h-S178D in plant protoplasts specifically upregulates uORF-mRNA translation. We propose that TOR functions in polysomes to maintain the active S6K1 (and thus eIF3h) phosphorylation status that is critical for translation reinitiation.
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Affiliation(s)
- Mikhail Schepetilnikov
- Institut de Biologie Moléculaire des Plantes du CNRS, Université de Strasbourg, Strasbourg Cedex 67084, France
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Moriwaki T, Miyazawa Y, Kobayashi A, Takahashi H. Molecular mechanisms of hydrotropism in seedling roots of Arabidopsis thaliana (Brassicaceae). AMERICAN JOURNAL OF BOTANY 2013; 100:25-34. [PMID: 23263156 DOI: 10.3732/ajb.1200419] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Roots show positive hydrotropism in response to moisture gradients, which is believed to contribute to plant water acquisition. This article reviews the recent advances of the physiological and molecular genetic studies on hydrotropism in seedling roots of Arabidopsis thaliana. We identified MIZU-KUSSEI1 (MIZ1) and MIZ2, essential genes for hydrotropism in roots; the former encodes a protein of unknown function, and the latter encodes an ARF-GEF (GNOM) protein involved in vesicle trafficking. Because both mutants are defective in hydrotropism but not in gravitropism, these mutations might affect a molecular mechanism unique to hydrotropism. MIZ1 is expressed in the lateral root cap and cortex of the root proper. It is localized as a soluble protein in the cytoplasm and in association with the cytoplasmic face of endoplasmic reticulum (ER) membranes in root cells. Light and ABA independently regulate MIZ1 expression, which influences the ultimate hydrotropic response. In addition, MIZ1 overexpression results in an enhancement of hydrotropism and an inhibition of lateral root formation. This phenotype is likely related to the alteration of auxin content in roots. Specifically, the auxin level in the roots decreases in the MIZ1 overexpressor and increases in the miz1 mutant. Unlike most gnom mutants, miz2 displays normal morphology, growth, and gravitropism, with normal localization of PIN proteins. It is probable that MIZ1 plays a crucial role in hydrotropic response by regulating the endogenous level of auxin in Arabidopsis roots. Furthermore, the role of GNOM/MIZ2 in hydrotropism is distinct from that of gravitropism.
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Affiliation(s)
- Teppei Moriwaki
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
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Paul AL, Wheeler RM, Levine HG, Ferl RJ. Fundamental plant biology enabled by the space shuttle. AMERICAN JOURNAL OF BOTANY 2013; 100:226-34. [PMID: 23281389 DOI: 10.3732/ajb.1200338] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The relationship between fundamental plant biology and space biology was especially synergistic in the era of the Space Shuttle. While all terrestrial organisms are influenced by gravity, the impact of gravity as a tropic stimulus in plants has been a topic of formal study for more than a century. And while plants were parts of early space biology payloads, it was not until the advent of the Space Shuttle that the science of plant space biology enjoyed expansion that truly enabled controlled, fundamental experiments that removed gravity from the equation. The Space Shuttle presented a science platform that provided regular science flights with dedicated plant growth hardware and crew trained in inflight plant manipulations. Part of the impetus for plant biology experiments in space was the realization that plants could be important parts of bioregenerative life support on long missions, recycling water, air, and nutrients for the human crew. However, a large part of the impetus was that the Space Shuttle enabled fundamental plant science essentially in a microgravity environment. Experiments during the Space Shuttle era produced key science insights on biological adaptation to spaceflight and especially plant growth and tropisms. In this review, we present an overview of plant science in the Space Shuttle era with an emphasis on experiments dealing with fundamental plant growth in microgravity. This review discusses general conclusions from the study of plant spaceflight biology enabled by the Space Shuttle by providing historical context and reviews of select experiments that exemplify plant space biology science.
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Affiliation(s)
- Anna-Lisa Paul
- Horticultural Science Department, University of Florida, Gainesville, Florida 32610, USA
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Abstract
While water shortage remains the single-most important factor influencing world agriculture, there are very few studies on how plants grow in response to water potential, i.e., hydrotropism. Terrestrial plant roots dwell in the soil, and their ability to grow and explore underground requires many sensors for stimuli such as gravity, humidity gradients, light, mechanical stimulations, temperature, and oxygen. To date, extremely limited information is available on the components of such sensors; however, all of these stimuli are sensed in the root cap. Directional growth of roots is controlled by gravity, which is fixed in direction and intensity. However, other environmental factors, such as water potential gradients, which fluctuate in time, space, direction, and intensity, can act as a signal for modifying the direction of root growth accordingly. Hydrotropism may help roots to obtain water from the soil and at the same time may participate in the establishment of the root system. Current genetic analysis of hydrotropism in Arabidopsis has offered new players, mainly AHR1, NHR1, MIZ1, and MIZ2, which seem to modulate how root caps sense and choose to respond hydrotropically as opposed to other tropic responses. Here we review the mechanism(s) by which these genes and the plant hormones abscisic acid and cytokinins coordinate hydrotropism to counteract the tropic responses to gravitational field, light or touch stimuli. The biological consequence of hydrotropism is also discussed in relation to water stress avoidance.
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Affiliation(s)
- Gladys I Cassab
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Col. Chamilpa, Cuernavaca, Mor. 62250 México.
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Miyazawa Y, Moriwaki T, Uchida M, Kobayashi A, Fujii N, Takahashi H. Overexpression of MIZU-KUSSEI1 enhances the root hydrotropic response by retaining cell viability under hydrostimulated conditions in Arabidopsis thaliana. PLANT & CELL PHYSIOLOGY 2012; 53:1926-1933. [PMID: 23012350 DOI: 10.1093/pcp/pcs129] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Because of their sessile nature, plants evolved several mechanisms to tolerate or avoid conditions where water is scarce. The molecular mechanisms contributing to drought tolerance have been studied extensively, whereas the molecular mechanism underlying drought avoidance is less understood despite its importance. Several lines of evidence showed that the roots sense the moisture gradient and grow toward the wet area: so-called hydrotropism. We previously identified MIZU-KUSSEI (MIZ) 1 and MIZ2/GNOM as genes responsible for this process. To gain new insight into the molecular mechanism of root hydrotropism, we generated overexpressors of MIZ1 (MIZ1OEs) and analyzed their hydrotropic response. MIZ1OEs had a remarkable enhancement of root hydrotropism. Furthermore, a greater number of MIZ1OE root cells remained viable under hydrostimulated conditions than those of the wild type, which might contribute to retaining root growth under hydrostimulated conditions. Although overexpression of MIZ1 also caused a slight decrease in the root gravitropic response, it was not attributable to the enhanced hydrotropic response. In addition, miz2 mutation or the auxin response inhibitor nullified the enhanced hydrotropic response in MIZ1OEs. Furthermore, the expression of MIZ1 did not alter the expression of typical genes involved in drought tolerance. These results suggest that MIZ1 positively regulates hydrotropism at an early stage and its overexpression results in an enhancement of signal transduction unique to root hydrotropism to increase the degree of hydrotropic root bending.
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Affiliation(s)
- Yutaka Miyazawa
- Graduate School of Life Sciences, Tohoku Unievrsity, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577 Japan.
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Nakayama M, Kaneko Y, Miyazawa Y, Fujii N, Higashitani N, Wada S, Ishida H, Yoshimoto K, Shirasu K, Yamada K, Nishimura M, Takahashi H. A possible involvement of autophagy in amyloplast degradation in columella cells during hydrotropic response of Arabidopsis roots. PLANTA 2012; 236:999-1012. [PMID: 22532286 DOI: 10.1007/s00425-012-1655-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Accepted: 04/11/2012] [Indexed: 05/31/2023]
Abstract
Seedling roots display not only gravitropism but also hydrotropism, and the two tropisms interfere with one another. In Arabidopsis (Arabidopsis thaliana) roots, amyloplasts in columella cells are rapidly degraded during the hydrotropic response. Degradation of amyloplasts involved in gravisensing enhances the hydrotropic response by reducing the gravitropic response. However, the mechanism by which amyloplasts are degraded in hydrotropically responding roots remains unknown. In this study, the mechanistic aspects of the degradation of amyloplasts in columella cells during hydrotropic response were investigated by analyzing organellar morphology, cell polarity and changes in gene expression. The results showed that hydrotropic stimulation or systemic water stress caused dramatic changes in organellar form and positioning in columella cells. Specifically, the columella cells of hydrotropically responding or water-stressed roots lost polarity in the distribution of the endoplasmic reticulum (ER), and showed accelerated vacuolization and nuclear movement. Analysis of ER-localized GFP showed that ER redistributed around the developed vacuoles. Cells often showed decomposing amyloplasts in autophagosome-like structures. Both hydrotropic stimulation and water stress upregulated the expression of AtATG18a, which is required for autophagosome formation. Furthermore, analysis with GFP-AtATG8a revealed that both hydrotropic stimulation and water stress induced the formation of autophagosomes in the columella cells. In addition, expression of plastid marker, pt-GFP, in the columella cells dramatically decreased in response to both hydrotropic stimulation and water stress, but its decrease was much less in the autophagy mutant atg5. These results suggest that hydrotropic stimulation confers water stress in the roots, which triggers an autophagic response responsible for the degradation of amyloplasts in columella cells of Arabidopsis roots.
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Affiliation(s)
- Mayumi Nakayama
- Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan
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Guyomarc'h S, Léran S, Auzon-Cape M, Perrine-Walker F, Lucas M, Laplaze L. Early development and gravitropic response of lateral roots in Arabidopsis thaliana. Philos Trans R Soc Lond B Biol Sci 2012; 367:1509-16. [PMID: 22527393 DOI: 10.1098/rstb.2011.0231] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Root system architecture plays an important role in determining nutrient and water acquisition and is modulated by endogenous and environmental factors, resulting in considerable developmental plasticity. The orientation of primary root growth in response to gravity (gravitropism) has been studied extensively, but little is known about the behaviour of lateral roots in response to this signal. Here, we analysed the response of lateral roots to gravity and, consistently with previous observations, we showed that gravitropism was acquired slowly after emergence. Using a lateral root induction system, we studied the kinetics for the appearance of statoliths, phloem connections and auxin transporter gene expression patterns. We found that statoliths could not be detected until 1 day after emergence, whereas the gravitropic curvature of the lateral root started earlier. Auxin transporters modulate auxin distribution in primary root gravitropism. We found differences regarding PIN3 and AUX1 expression patterns between the lateral root and the primary root apices. Especially PIN3, which is involved in primary root gravitropism, was not expressed in the lateral root columella. Our work revealed new developmental transitions occurring in lateral roots after emergence, and auxin transporter expression patterns that might explain the specific response of lateral roots to gravity.
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Affiliation(s)
- S Guyomarc'h
- Université Montpellier 2, UMR DIADE, Equipe Rhizogenèse, 911 Avenue Agropolis, 34394 Montpellier cedex 5, France
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Zou N, Li B, Dong G, Kronzucker HJ, Shi W. Ammonium-induced loss of root gravitropism is related to auxin distribution and TRH1 function, and is uncoupled from the inhibition of root elongation in Arabidopsis. JOURNAL OF EXPERIMENTAL BOTANY 2012; 63:3777-88. [PMID: 22407650 DOI: 10.1093/jxb/ers068] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Root gravitropism is affected by many environmental stresses, including salinity, drought, and nutrient deficiency. One significant environmental stress, excess ammonium (NH(4)(+)), is well documented to inhibit root elongation and lateral root formation, yet little is known about its effects on the direction of root growth. We show here that inhibition of root elongation upon elevation of external NH(4)(+) is accompanied by a loss in root gravitropism (agravitropism) in Arabidopsis. Addition of potassium (K(+)) to the treatment medium partially rescued the inhibition of root elongation by high NH(4)(+) but did not improve gravitropic root curvature. Expression analysis of the auxin-responsive reporter gene DR5::GUS revealed that NH(4)(+) treatment delayed the development of gravity-induced auxin gradients across the root cap but extended their duration once initiated. Moreover, the β-glucuronidase (GUS) signal intensity in root tip cells was significantly reduced under high NH(4)(+) treatment over time. The potassium carrier mutant trh1 displayed different patterns of root gravitropism and DR5::GUS signal intensity in root apex cells compared with the wild type in response to NH(4)(+). Together, the results demonstrate that the effects of NH(4)(+) on root gravitropism are related to delayed lateral auxin redistribution and the TRH1 pathway, and are largely independent of inhibitory effects on root elongation.
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Affiliation(s)
- Na Zou
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
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Saucedo M, Ponce G, Campos ME, Eapen D, García E, Luján R, Sánchez Y, Cassab GI. An altered hydrotropic response (ahr1) mutant of Arabidopsis recovers root hydrotropism with cytokinin. JOURNAL OF EXPERIMENTAL BOTANY 2012; 63:3587-601. [PMID: 22442413 PMCID: PMC3388826 DOI: 10.1093/jxb/ers025] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Revised: 12/08/2011] [Accepted: 01/17/2012] [Indexed: 05/19/2023]
Abstract
Roots are highly plastic and can acclimate to heterogeneous and stressful conditions. However, there is little knowledge of the effect of moisture gradients on the mechanisms controlling root growth orientation and branching, and how this mechanism may help plants to avoid drought responses. The aim of this study was to isolate mutants of Arabidopsis thaliana with altered hydrotropic responses. Here, altered hydrotropic response 1 (ahr1), a semi-dominant allele segregating as a single gene mutation, was characterized. ahr1 directed the growth of its primary root towards the source of higher water availability and developed an extensive root system over time. This phenotype was intensified in the presence of abscisic acid and was not observed if ahr1 seedlings were grown in a water stress medium without a water potential gradient. In normal growth conditions, primary root growth and root branching of ahr1 were indistinguishable from those of the wild type (wt). The altered hydrotropic growth of ahr1 roots was confirmed when the water-rich source was placed at an angle of 45° from the gravity vector. In this system, roots of ahr1 seedlings grew downward and did not display hydrotropism; however, in the presence of cytokinins, they exhibited hydrotropism like those of the wt, indicating that cytokinins play a critical role in root hydrotropism. The ahr1 mutant represents a valuable genetic resource for the study of the effects of cytokinins in the differential growth of hydrotropism and control of lateral root formation during the hydrotropic response.
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Affiliation(s)
- Manuel Saucedo
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico
| | - Georgina Ponce
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico
| | - María Eugenia Campos
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico
| | - Delfeena Eapen
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico
| | - Edith García
- Colegio de Postgraduados, Carretera México-Texcoco Km. 36.5, Montecillo, Texcoco, Estado de México 56230, México
| | - Rosario Luján
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico
| | - Yoloxóchitl Sánchez
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico
| | - Gladys I. Cassab
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico
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Strohm AK, Baldwin KL, Masson PH. Molecular mechanisms of root gravity sensing and signal transduction. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2011; 1:276-85. [PMID: 23801441 DOI: 10.1002/wdev.14] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Plants use gravity as a guide to direct their roots down into the soil to anchor themselves and to find resources needed for growth and development. In higher plants, the columella cells of the root tip form the primary site of gravity sensing, and in these cells the sedimentation of dense, starch-filled plastids (amyloplasts) triggers gravity signal transduction. This generates an auxin gradient across the root cap that is transmitted to the elongation zone where it promotes differential cell elongation, allowing the root to direct itself downward. It is still not well understood how amyloplast sedimentation leads to auxin redistribution. Models have been proposed to explain how mechanosensitive ion channels or ligand-receptor interactions could connect these events. Although their roles are still unclear, possible second messengers in this process include protons, Ca(2+), and inositol 1,4,5-triphosphate. Upon gravistimulation, the auxin efflux facilitators PIN3 and PIN7 relocalize to the lower side of the columella cells and mediate auxin redistribution. However, evidence for an auxin-independent secondary mechanism of gravity sensing and signal transduction suggests that this physiological process is quite complex. Furthermore, plants must integrate a variety of environmental cues, resulting in multifaceted relationships between gravitropism and other directional growth responses such as hydro-, photo-, and thigmotropism.
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