1
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Scott CB, Ostling A, Matz MV. Should I stay or should I go? Coral bleaching from the symbionts' perspective. Ecol Lett 2024; 27:e14429. [PMID: 38690608 DOI: 10.1111/ele.14429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 04/08/2024] [Accepted: 04/10/2024] [Indexed: 05/02/2024]
Abstract
Coral bleaching, the stress-induced breakdown of coral-algal symbiosis, threatens reefs globally. Paradoxically, despite adverse fitness effects, corals bleach annually, even outside of abnormal temperatures. This generally occurs shortly after the once-per-year mass coral spawning. Here, we propose a hypothesis linking annual coral bleaching and the transmission of symbionts to the next generation of coral hosts. We developed a dynamic model with two symbiont growth strategies, and found that high sexual recruitment and low adult coral survivorship and growth favour bleaching susceptibility, while the reverse promotes bleaching resilience. Otherwise, unexplained trends in the Indo-Pacific align with our hypothesis, where reefs and coral taxa exhibiting higher recruitment are more bleaching susceptible. The results from our model caution against interpreting potential shifts towards more bleaching-resistant symbionts as evidence of climate adaptation-we predict such a shift could also occur in declining systems experiencing low recruitment rates, a common scenario on today's reefs.
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Affiliation(s)
- Carly B Scott
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas, USA
| | - Annette Ostling
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas, USA
| | - Mikhail V Matz
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas, USA
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2
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Sakamoto K, Ogiwara N, Kaji T, Sugimoto Y, Ueno M, Sonoda M, Matsui A, Ishida J, Tanaka M, Totoki Y, Shinozaki K, Seki M. Transcriptome analysis of soybean (Glycine max) root genes differentially expressed in rhizobial, arbuscular mycorrhizal, and dual symbiosis. JOURNAL OF PLANT RESEARCH 2019; 132:541-568. [PMID: 31165947 DOI: 10.1007/s10265-019-01117-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Accepted: 05/25/2019] [Indexed: 05/11/2023]
Abstract
Soybean (Glycine max) roots establish associations with nodule-inducing rhizobia and arbuscular mycorrhizal (AM) fungi. Both rhizobia and AM fungi have been shown to affect the activity of and colonization by the other, and their interactions can be detected within host plants. Here, we report the transcription profiles of genes differentially expressed in soybean roots in the presence of rhizobial, AM, or rhizobial-AM dual symbiosis, compared with those in control (uninoculated) roots. Following inoculation, soybean plants were grown in a glasshouse for 6 weeks; thereafter their root transcriptomes were analyzed using an oligo DNA microarray. Among the four treatments, the root nodule number and host plant growth were highest in plants with dual symbiosis. We observed that the expression of 187, 441, and 548 host genes was up-regulated and 119, 1,439, and 1,298 host genes were down-regulated during rhizobial, AM, and dual symbiosis, respectively. The expression of 34 host genes was up-regulated in each of the three symbioses. These 34 genes encoded several membrane transporters, type 1 metallothionein, and transcription factors in the MYB and bHLH families. We identified 56 host genes that were specifically up-regulated during dual symbiosis. These genes encoded several nodulin proteins, phenylpropanoid metabolism-related proteins, and carbonic anhydrase. The nodulin genes up-regulated by the AM fungal colonization probably led to the observed increases in root nodule number and host plant growth. Some other nodulin genes were down-regulated specifically during AM symbiosis. Based on the results above, we suggest that the contribution of AM fungal colonization is crucial to biological N2-fixation and host growth in soybean with rhizobial-AM dual symbiosis.
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Affiliation(s)
- Kazunori Sakamoto
- Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba, 271-8510, Japan.
| | - Natsuko Ogiwara
- Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba, 271-8510, Japan
| | - Tomomitsu Kaji
- JA ZEN-NOH Research and Development Center, 4-18-1 Higashiyawata, Hiratsuka, Kanagawa, 254-0016, Japan
| | - Yurie Sugimoto
- Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba, 271-8510, Japan
| | - Mitsuru Ueno
- Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba, 271-8510, Japan
| | - Masatoshi Sonoda
- Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba, 271-8510, Japan
| | - Akihiro Matsui
- RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan
- RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - Junko Ishida
- RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan
- RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - Maho Tanaka
- RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan
- RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - Yasushi Totoki
- Division of Cancer Genomics, National Cancer Center Research Institute, Chuo-ku, Tokyo, 104-0045, Japan
| | - Kazuo Shinozaki
- RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan
| | - Motoaki Seki
- RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan
- RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
- Kihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Totsuka-ku, Yokohama, Kanagawa, 244-0813, Japan
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3
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Coba de la Peña T, Fedorova E, Pueyo JJ, Lucas MM. The Symbiosome: Legume and Rhizobia Co-evolution toward a Nitrogen-Fixing Organelle? FRONTIERS IN PLANT SCIENCE 2018; 8:2229. [PMID: 29403508 PMCID: PMC5786577 DOI: 10.3389/fpls.2017.02229] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Accepted: 12/19/2017] [Indexed: 05/21/2023]
Abstract
In legume nodules, symbiosomes containing endosymbiotic rhizobial bacteria act as temporary plant organelles that are responsible for nitrogen fixation, these bacteria develop mutual metabolic dependence with the host legume. In most legumes, the rhizobia infect post-mitotic cells that have lost their ability to divide, although in some nodules cells do maintain their mitotic capacity after infection. Here, we review what is currently known about legume symbiosomes from an evolutionary and developmental perspective, and in the context of the different interactions between diazotroph bacteria and eukaryotes. As a result, it can be concluded that the symbiosome possesses organelle-like characteristics due to its metabolic behavior, the composite origin and differentiation of its membrane, the retargeting of host cell proteins, the control of microsymbiont proliferation and differentiation by the host legume, and the cytoskeletal dynamics and symbiosome segregation during the division of rhizobia-infected cells. Different degrees of symbiosome evolution can be defined, specifically in relation to rhizobial infection and to the different types of nodule. Thus, our current understanding of the symbiosome suggests that it might be considered a nitrogen-fixing link in organelle evolution and that the distinct types of legume symbiosomes could represent different evolutionary stages toward the generation of a nitrogen-fixing organelle.
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Affiliation(s)
- Teodoro Coba de la Peña
- Instituto de Ciencias Agrarias ICA-CSIC, Madrid, Spain
- Centro de Estudios Avanzados en Zonas Áridas (CEAZA), La Serena, Chile
| | - Elena Fedorova
- Instituto de Ciencias Agrarias ICA-CSIC, Madrid, Spain
- K. A. Timiryazev Institute of Plant Physiology, Russian Academy of Science, Moscow, Russia
| | - José J Pueyo
- Instituto de Ciencias Agrarias ICA-CSIC, Madrid, Spain
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4
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Subramanian S, Souleimanov A, Smith DL. Proteomic Studies on the Effects of Lipo-Chitooligosaccharide and Thuricin 17 under Unstressed and Salt Stressed Conditions in Arabidopsis thaliana. FRONTIERS IN PLANT SCIENCE 2016; 7:1314. [PMID: 27625672 PMCID: PMC5003918 DOI: 10.3389/fpls.2016.01314] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 08/16/2016] [Indexed: 05/18/2023]
Abstract
Plants, being sessile organisms, are exposed to widely varying environmental conditions throughout their life cycle. Compatible plant-microbe interactions favor plant growth and development, and help plants deal with these environmental challenges. Microorganisms produce a diverse range of elicitor molecules to establish symbiotic relationships with the plants they associate with, in a given ecological niche. Lipo-chitooligosaccharide (LCO) and Thuricin 17 (Th17) are two such compounds shown to positively influence plant growth of both legumes and non-legumes. Arabidopsis thaliana responded positively to treatment with the bacterial signal compounds LCO and Th17 in the presence of salt stress (up to 250 mM NaCl). Shotgun proteomics of unstressed and 250 mM NaCl stressed A. thaliana rosettes (7 days post stress) in combination with the LCO and Th17 revealed many known, putative, hypothetical, and unknown proteins. Overall, carbon and energy metabolic pathways were affected under both unstressed and salt stressed conditions when treated with these signals. PEP carboxylase, Rubisco-oxygenase large subunit, pyruvate kinase, and proteins of photosystems I and II were some of the noteworthy proteins enhanced by the signals, along with other stress related proteins. These findings suggest that the proteome of A. thaliana rosettes is altered by the bacterial signals tested, and more so under salt stress, thereby imparting a positive effect on plant growth under high salt stress. The roles of the identified proteins are discussed here in relation to salt stress adaptation, which, when translated to field grown crops can be a crucial component and of significant importance in agriculture and global food production. The mass spectrometry proteomics data have been deposited to the ProteomeXchange with identifier PXD004742.
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Affiliation(s)
| | | | - Donald L. Smith
- Department of Plant Science, McGill UniversityMontréal, QC, Canada
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5
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Nouri E, Reinhardt D. Flowers and mycorrhizal roots--closer than we think? TRENDS IN PLANT SCIENCE 2015; 20:344-50. [PMID: 25868653 DOI: 10.1016/j.tplants.2015.03.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Revised: 03/11/2015] [Accepted: 03/18/2015] [Indexed: 05/24/2023]
Abstract
Roots and flowers are formed at the extreme ends of plants and they differ in almost every aspect of their development and function; even so, they exhibit surprising molecular commonalities. For example, the calcium and calmodulin-dependent protein kinase (CCaMK) plays a central role in root symbioses with fungi and bacteria, but is also highly expressed in developing anthers. Moreover, independent evidence from transcriptomics, phylogenomics, and genetics reveals common developmental elements in root symbioses and reproductive development. We discuss the significance of these overlaps, and we argue that an integrated comparative view of the two phenomena will stimulate research and provide new insight, not only into shared components, but also into the specific aspects of anther development and root symbioses.
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Affiliation(s)
- Eva Nouri
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Didier Reinhardt
- Department of Biology, University of Fribourg, Fribourg, Switzerland.
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6
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Soyano T, Hayashi M. Transcriptional networks leading to symbiotic nodule organogenesis. CURRENT OPINION IN PLANT BIOLOGY 2014; 20:146-54. [PMID: 25113465 DOI: 10.1016/j.pbi.2014.07.010] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2014] [Revised: 07/17/2014] [Accepted: 07/18/2014] [Indexed: 05/08/2023]
Abstract
The symbiosis with nitrogen-fixing bacteria leading to root nodules is a relatively recent evolutionary innovation and limited to a distinct order of land plants. It has long been a mystery how plants have invented this complex trait. However, recent advances in molecular genetics of model legumes has elucidated genes involved in the development of root nodules, providing insights into this process. Here we discuss how the de novo assembly of transcriptional networks may account for the predisposition to nodulate. Transcriptional networks and modes of gene regulation from the arbuscular mycorrhizal symbiosis, nitrate responses and aspects of lateral root development have likely all contributed to the emergence and development of root nodules.
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Affiliation(s)
- Takashi Soyano
- Plant Symbiosis Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-3602, Japan
| | - Makoto Hayashi
- Plant Symbiosis Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-3602, Japan.
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7
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Held M, Hou H, Miri M, Huynh C, Ross L, Hossain MS, Sato S, Tabata S, Perry J, Wang TL, Szczyglowski K. Lotus japonicus cytokinin receptors work partially redundantly to mediate nodule formation. THE PLANT CELL 2014; 26:678-94. [PMID: 24585837 PMCID: PMC3967033 DOI: 10.1105/tpc.113.119362] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Revised: 01/22/2014] [Accepted: 02/05/2014] [Indexed: 05/21/2023]
Abstract
Previous analysis of the Lotus histidine kinase1 (Lhk1) cytokinin receptor gene has shown that it is required and also sufficient for nodule formation in Lotus japonicus. The L. japonicus mutant carrying the loss-of-function lhk1-1 allele is hyperinfected by its symbiotic partner, Mesorhizobium loti, in the initial absence of nodule organogenesis. At a later time point following bacterial infection, lhk1-1 develops a limited number of nodules, suggesting the presence of an Lhk1-independent mechanism. We have tested a hypothesis that other cytokinin receptors function in at least a partially redundant manner with LHK1 to mediate nodule organogenesis in L. japonicus. We show here that L. japonicus contains a small family of four cytokinin receptor genes, which all respond to M. loti infection. We show that within the root cortex, LHK1 performs an essential role but also works partially redundantly with LHK1A and LHK3 to mediate cell divisions for nodule primordium formation. The LHK1 receptor is also presumed to partake in mediating a feedback mechanism that negatively regulates bacterial infections at the root epidermis. Interestingly, the Arabidopsis thaliana AHK4 receptor gene can functionally replace Lhk1 in mediating nodule organogenesis, indicating that the ability to perform this developmental process is not determined by unique, legume-specific properties of LHK1.
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MESH Headings
- Alleles
- Arabidopsis/drug effects
- Arabidopsis/growth & development
- Cytokinins/metabolism
- Cytokinins/pharmacology
- Escherichia coli
- Gene Expression Regulation, Plant/drug effects
- Lotus/drug effects
- Lotus/genetics
- Lotus/growth & development
- Lotus/microbiology
- Mesorhizobium
- Models, Biological
- Molecular Sequence Data
- Multigene Family
- Mutation/genetics
- Organogenesis/drug effects
- Organogenesis/genetics
- Phylogeny
- Plant Proteins/chemistry
- Plant Proteins/metabolism
- Promoter Regions, Genetic/genetics
- Protein Structure, Tertiary
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptors, Cell Surface/chemistry
- Receptors, Cell Surface/metabolism
- Root Nodules, Plant/drug effects
- Root Nodules, Plant/growth & development
- Root Nodules, Plant/microbiology
- Saccharomyces cerevisiae/genetics
- Signal Transduction/drug effects
- Signal Transduction/genetics
- Transcription, Genetic/drug effects
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Affiliation(s)
- Mark Held
- Agriculture and Agri-Food Canada, Southern Crop
Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
- Department of Biology, University of Western Ontario,
London, Ontario N6A 5BF, Canada
| | - Hongwei Hou
- Agriculture and Agri-Food Canada, Southern Crop
Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
| | - Mandana Miri
- Agriculture and Agri-Food Canada, Southern Crop
Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
- Department of Biology, University of Western Ontario,
London, Ontario N6A 5BF, Canada
| | - Christian Huynh
- Agriculture and Agri-Food Canada, Southern Crop
Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
| | - Loretta Ross
- Agriculture and Agri-Food Canada, Southern Crop
Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
| | - Md Shakhawat Hossain
- Agriculture and Agri-Food Canada, Southern Crop
Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
| | - Shusei Sato
- Kazusa DNA Research Institute, Kisarazu, Chiba 292-0818,
Japan
| | - Satoshi Tabata
- Kazusa DNA Research Institute, Kisarazu, Chiba 292-0818,
Japan
| | | | | | - Krzysztof Szczyglowski
- Agriculture and Agri-Food Canada, Southern Crop
Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
- Department of Biology, University of Western Ontario,
London, Ontario N6A 5BF, Canada
- Address correspondence to
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8
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Held M, Hou H, Miri M, Huynh C, Ross L, Hossain MS, Sato S, Tabata S, Perry J, Wang TL, Szczyglowski K. Lotus japonicus cytokinin receptors work partially redundantly to mediate nodule formation. THE PLANT CELL 2014. [PMID: 24585837 DOI: 10.1105/tpc.113.119382] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Previous analysis of the Lotus histidine kinase1 (Lhk1) cytokinin receptor gene has shown that it is required and also sufficient for nodule formation in Lotus japonicus. The L. japonicus mutant carrying the loss-of-function lhk1-1 allele is hyperinfected by its symbiotic partner, Mesorhizobium loti, in the initial absence of nodule organogenesis. At a later time point following bacterial infection, lhk1-1 develops a limited number of nodules, suggesting the presence of an Lhk1-independent mechanism. We have tested a hypothesis that other cytokinin receptors function in at least a partially redundant manner with LHK1 to mediate nodule organogenesis in L. japonicus. We show here that L. japonicus contains a small family of four cytokinin receptor genes, which all respond to M. loti infection. We show that within the root cortex, LHK1 performs an essential role but also works partially redundantly with LHK1A and LHK3 to mediate cell divisions for nodule primordium formation. The LHK1 receptor is also presumed to partake in mediating a feedback mechanism that negatively regulates bacterial infections at the root epidermis. Interestingly, the Arabidopsis thaliana AHK4 receptor gene can functionally replace Lhk1 in mediating nodule organogenesis, indicating that the ability to perform this developmental process is not determined by unique, legume-specific properties of LHK1.
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MESH Headings
- Alleles
- Arabidopsis/drug effects
- Arabidopsis/growth & development
- Cytokinins/metabolism
- Cytokinins/pharmacology
- Escherichia coli
- Gene Expression Regulation, Plant/drug effects
- Lotus/drug effects
- Lotus/genetics
- Lotus/growth & development
- Lotus/microbiology
- Mesorhizobium
- Models, Biological
- Molecular Sequence Data
- Multigene Family
- Mutation/genetics
- Organogenesis/drug effects
- Organogenesis/genetics
- Phylogeny
- Plant Proteins/chemistry
- Plant Proteins/metabolism
- Promoter Regions, Genetic/genetics
- Protein Structure, Tertiary
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptors, Cell Surface/chemistry
- Receptors, Cell Surface/metabolism
- Root Nodules, Plant/drug effects
- Root Nodules, Plant/growth & development
- Root Nodules, Plant/microbiology
- Saccharomyces cerevisiae/genetics
- Signal Transduction/drug effects
- Signal Transduction/genetics
- Transcription, Genetic/drug effects
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Affiliation(s)
- Mark Held
- Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London, Ontario N5V 4T3, Canada
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9
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Foo E, Ferguson BJ, Reid JB. Common and divergent roles of plant hormones in nodulation and arbuscular mycorrhizal symbioses. PLANT SIGNALING & BEHAVIOR 2014; 9:e29593. [PMID: 25763697 PMCID: PMC4205148 DOI: 10.4161/psb.29593] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 06/16/2014] [Indexed: 05/20/2023]
Abstract
All of the classical plant hormones have been suggested to influence nodulation, including some that interact with the Autoregulation of Nodulation (AON) pathway. Leguminous plants strictly regulate the number of nodules formed through this AON pathway via a root-shoot-root loop that acts to suppress excessive nodulation. A related pathway, the Autoregulation of Mycorrhization (AOM) pathway controls the more ancient, arbuscular mycorrhizal (AM) symbiosis. A comparison of the published responses to the classical hormones in these 2 symbioses shows that most influence the symbioses in the same direction. This may be expected if they affect the symbioses via common components of these symbiotic regulatory pathways. However, some hormones influence these symbioses in opposite directions, suggesting a more complex relationship, and probably one that is not via the common components of these pathways. In a recent paper we showed, using a genetic approach, that strigolactones and brassinosteroids do not act downstream of the AON genes examined and argued that they probably act independently to promote nodule formation. Recently it has been shown that the control of nodulation via the AON pathway involves mobile CLE peptide signals. It is therefore suggested that a more direct avenue to determine if the classical hormones play a direct role in the autoregulatory pathways is to further examine whether CLE peptides and other components of these processes can influence, or be influenced by, the classical hormones. Such studies and other comparisons between the nodulation and mycorrhizal symbioses should allow the role of the classical hormones in these critical symbioses to be rapidly advanced.
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Affiliation(s)
- Eloise Foo
- School of Biological Sciences; University of Tasmania; TAS Australia
- Correspondence to: Eloise Foo,
| | - Brett J Ferguson
- Centre for Integrative Legume Research, School of Agriculture and Food Sciences; The University of Queensland; St Lucia, Brisbane, QLD Australia
| | - James B Reid
- School of Biological Sciences; University of Tasmania; TAS Australia
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10
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Sanchez-Lopez R, Jáuregui D, Quinto C. SymRK and the nodule vascular system: an underground connection. PLANT SIGNALING & BEHAVIOR 2012; 7:691-3. [PMID: 22580688 PMCID: PMC3442870 DOI: 10.4161/psb.20181] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Symbiotic legume-rhizobia relationship leads to the formation of nitrogen-fixing nodules. Successful nodulation depends on the expression and cross-talk of a batttery of genes, among them SymRK (symbiosis receptor-like kinase), a leucine-rich repeat receptor-like kinase. SymRK is required for the rhizobia invasion of root hairs, as well as for the infection thread and symbiosome formation. Using immunolocalization and downregulation strategies we have recently provided evidence of a new function of PvSymRK in nodulation. We have found that a tight regulation of PvSymRK expression is required for the accurate development of the vascular bundle system in Phaseolus vulgaris nodules.
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11
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Sánchez-López R, Jáuregui D, Nava N, Alvarado-Affantranger X, Montiel J, Santana O, Sanchez F, Quinto C. Down-regulation of SymRK correlates with a deficiency in vascular bundle development in Phaseolus vulgaris nodules. PLANT, CELL & ENVIRONMENT 2011; 34:2109-21. [PMID: 21848862 DOI: 10.1111/j.1365-3040.2011.02408.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The symbiotic interaction of legumes and rhizobia results in the formation of nitrogen-fixing nodules. Nodulation depends on the finely coordinated expression of a battery of genes involved in the infection and the organogenesis processes. After Nod factor perception, symbiosis receptor kinase (SymRK) receptor triggers a signal transduction cascade essential for nodulation leading to cortical cell divisions, infection thread (IT) formation and final release of rhizobia to the intracellular space, forming the symbiosome. Herein, the participation of SymRK receptor during the nodule organogenesis in Phaseolus vulgaris is addressed. Our findings indicate that besides its expression in the nodule epidermis, in IT, and in uninfected cells of the infection zone, PvSymRK immunolocalizes in the root and nodule vascular system. On the other hand, knockdown expression of PvSymRK led to the formation of scarce and defective nodules, which presented alterations in both IT/symbiosome formation and vascular system.
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Affiliation(s)
- Rosana Sánchez-López
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
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12
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Yokota K, Hayashi M. Function and evolution of nodulation genes in legumes. Cell Mol Life Sci 2011; 68:1341-51. [PMID: 21380559 PMCID: PMC11114672 DOI: 10.1007/s00018-011-0651-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 02/15/2011] [Accepted: 02/16/2011] [Indexed: 10/18/2022]
Abstract
Root nodule (RN) symbiosis has a unique feature in which symbiotic bacteria fix atmospheric nitrogen. The symbiosis is established with a limited species of land plants, including legumes. How RN symbiosis evolved is still a mystery, but recent findings on legumes genes that are necessary for RN symbiosis may give us a clue.
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Affiliation(s)
- Keisuke Yokota
- National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, Japan.
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13
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Held M, Hossain MS, Yokota K, Bonfante P, Stougaard J, Szczyglowski K. Common and not so common symbiotic entry. TRENDS IN PLANT SCIENCE 2010; 15:540-545. [PMID: 20829094 DOI: 10.1016/j.tplants.2010.08.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Revised: 07/26/2010] [Accepted: 08/09/2010] [Indexed: 05/29/2023]
Abstract
Great advances have been made in our understanding of the host plant's common symbiosis functions, which in legumes mediate intracellular accommodation of both nitrogen-fixing bacteria and arbuscular mycorrhiza (AM) fungi. However, it has become apparent that additional plant genes are required specifically for bacterial entry inside the host root. In this opinion article, we consider Lotus japonicus nap1 and pir1 symbiotic mutants within the context of other deleterious mutations that impair an intracellular accommodation of bacteria but have no impact on the colonization of roots by AM fungi. We highlight a clear delineation of early signaling events during bacterial versus AM symbioses while suggesting a more intricate origin of the plant's ability for intracellular accommodation of bacteria.
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Affiliation(s)
- Mark Held
- Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London, Ontario NV5 4T3, Canada
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14
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Maekawa-Yoshikawa M, Müller J, Takeda N, Maekawa T, Sato S, Tabata S, Perry J, Wang TL, Groth M, Brachmann A, Parniske M. The temperature-sensitive brush mutant of the legume Lotus japonicus reveals a link between root development and nodule infection by rhizobia. PLANT PHYSIOLOGY 2009; 149:1785-96. [PMID: 19176723 PMCID: PMC2663734 DOI: 10.1104/pp.108.135160] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/01/2009] [Accepted: 01/23/2009] [Indexed: 05/20/2023]
Abstract
The brush mutant of Lotus japonicus exhibits a temperature-dependent impairment in nodule, root, and shoot development. At 26 degrees C, brush formed fewer nodules, most of which were not colonized by rhizobia bacteria. Primary root growth was retarded and the anatomy of the brush root apical meristem revealed distorted cellular organization and reduced cell expansion. Reciprocal grafting of brush with wild-type plants indicated that this genotype only affected the root and that the shoot phenotype was a secondary effect. The root and nodulation phenotype cosegregated as a single Mendelian trait and the BRUSH gene could be mapped to the short arm of chromosome 2. At 18 degrees C, the brush root anatomy was rescued and similar to the wild type, and primary root length, number of infection threads, and nodule formation were partially rescued. Superficially, the brush root phenotype resembled the ethylene-related thick short root syndrome. However, treatment with ethylene inhibitor did not recover the observed phenotypes, although brush primary roots were slightly longer. The defects of brush in root architecture and infection thread development, together with intact nodule architecture and complete absence of symptoms from shoots, suggest that BRUSH affects cellular differentiation in a tissue-dependent way.
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15
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Sinharoy S, Saha S, Chaudhury SR, Dasgupta M. Transformed hairy roots of Arachis hypogea: a tool for studying root nodule symbiosis in a non-infection thread legume of the Aeschynomeneae tribe. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2009; 22:132-142. [PMID: 19132866 DOI: 10.1094/mpmi-22-2-0132] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Arachis hypogea is a non-"infection thread" (IT) legume where rhizobial entry or dissemination in the nodules never involves IT. Rhizobia invade through epidermal "cracks" and directly access the cortical cells to develop the characteristic aeschynomenoid nodules. For investigating these nonclassical nodulation features in Arachis spp., we developed an efficient procedure for Agrobacterium rhizogenes R1000-mediated transformation of this plant. In this study, we optimized the induction of hairy roots and nodulation of composite Arachis hypogea plants in the presence of Bradyrhizobium sp. (Arachis) strain NC92. 35S promoter-driven green fluorescent protein and beta-glucuronidase expression indicated transformation frequency to be above 80%. The transformed roots had the characteristic rosette-type root hairs and had normal level of expression of symbiosis-related genes SymRK and CCaMK. The transgenic nodules resembled the wild-type nodules with an exception of 2 to 3%, where they structurally deviated from the wild-type nodules to form nodular roots. A 16S rRNA profile of an infected-zone metagenome indicated that identical populations of bradyrhizobia invaded both composite wild-type plants grown in natural soil. Our results demonstrate that Arachis hairy root is an attractive system for undertaking investigations of the nonclassical features associated with its nitrogen-fixing symbiotic interactions.
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Affiliation(s)
- Senjuti Sinharoy
- Department of Biochemistry, Calcutta University, Calcutta, India
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16
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Crespi M, Frugier F. De Novo Organ Formation from Differentiated Cells: Root Nodule Organogenesis. Sci Signal 2008; 1:re11. [DOI: 10.1126/scisignal.149re11] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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17
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Osborne B, Bergman B. Why Does Gunnera Do It and Other Angiosperms Don't? An Evolutionary Perspective on the Gunnera–Nostoc Symbiosis. ACTA ACUST UNITED AC 2008. [DOI: 10.1007/7171_2007_116] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2023]
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18
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Capoen W, Den Herder J, Rombauts S, De Gussem J, De Keyser A, Holsters M, Goormachtig S. Comparative transcriptome analysis reveals common and specific tags for root hair and crack-entry invasion in Sesbania rostrata. PLANT PHYSIOLOGY 2007; 144:1878-89. [PMID: 17600136 PMCID: PMC1949896 DOI: 10.1104/pp.107.102178] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The tropical legume Sesbania rostrata provides its microsymbiont Azorhizobium caulinodans with versatile invasion strategies to allow nodule formation in temporarily flooded habitats. In aerated soils, the bacteria enter via the root hair curling mechanism. Submergence prevents this epidermal invasion by accumulation of inhibiting concentrations of ethylene and, under these conditions, the bacterial colonization occurs via intercellular cortical infection at lateral root bases. The transcriptome of both invasion ways was compared by cDNA-amplified fragment length polymorphism analysis. Clusters of gene tags were identified that were specific for either epidermal or cortical invasion or were shared by both. The data provide insight into mechanisms that control infection and illustrate that entry via the epidermis adds a layer of complexity to rhizobial invasion.
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Affiliation(s)
- Ward Capoen
- Department of Plant Systems Biology, Flanders Institute for Biotechnology, Ghent University, B-9052 Ghent, Belgium
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19
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Udvardi MK, Kakar K, Wandrey M, Montanari O, Murray J, Andriankaja A, Zhang JY, Benedito V, Hofer JMI, Chueng F, Town CD. Legume transcription factors: global regulators of plant development and response to the environment. PLANT PHYSIOLOGY 2007; 144:538-49. [PMID: 17556517 PMCID: PMC1914172 DOI: 10.1104/pp.107.098061] [Citation(s) in RCA: 162] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2007] [Accepted: 03/24/2007] [Indexed: 05/15/2023]
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20
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Pislariu CI, Dickstein R. An IRE-like AGC kinase gene, MtIRE, has unique expression in the invasion zone of developing root nodules in Medicago truncatula. PLANT PHYSIOLOGY 2007; 144:682-94. [PMID: 17237187 PMCID: PMC1914176 DOI: 10.1104/pp.106.092494] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Accepted: 01/01/2007] [Indexed: 05/13/2023]
Abstract
The AGC protein kinase family (cAMP-dependent protein kinases A, cGMP-dependent protein kinases G, and phospholipid-dependent protein kinases C) have important roles regulating growth and development in animals and fungi. They are activated via lipid second messengers by 3-phosphoinositide-dependent protein kinase coupling lipid signals to phosphorylation of the AGC kinases. These phosphorylate downstream signal transduction protein targets. AGC kinases are becoming better studied in plants, especially in Arabidopsis (Arabidopsis thaliana), where specific AGC kinases have been shown to have key roles in regulating growth signal pathways. We report here the isolation and characterization of the first AGC kinase gene identified in Medicago truncatula, MtIRE. It was cloned by homology with the Arabidopsis INCOMPLETE ROOT HAIR ELONGATION (IRE) gene. Semiquantitative reverse transcription-polymerase chain reaction analysis shows that, unlike its Arabidopsis counterpart, MtIRE is not expressed in uninoculated roots, but is expressed in root systems that have been inoculated with Sinorhizobium meliloti and are developing root nodules. MtIRE expression is also found in flowers. Expression analysis of a time course of nodule development and of nodulating root systems of many Medicago nodulation mutants shows MtIRE expression correlates with infected cell maturation during nodule development. During the course of these experiments, nine Medicago nodulation mutants, including sli and dnf1 to 7 mutants, were evaluated for the first time for their microscopic nodule phenotype using S. meliloti constitutively expressing lacZ. Spatial localization of a pMtIRE-gusA transgene in transformed roots of composite plants showed that MtIRE expression is confined to the proximal part of the invasion zone, zone II, found in indeterminate nodules. This suggests MtIRE is useful as an expression marker for this region of the invasion zone.
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Affiliation(s)
- Catalina I Pislariu
- University of North Texas, Department of Biological Sciences, Denton, Texas 76203-5220, USA
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21
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Khan JA, Wang Q, Sjölund RD, Schulz A, Thompson GA. An early nodulin-like protein accumulates in the sieve element plasma membrane of Arabidopsis. PLANT PHYSIOLOGY 2007; 143:1576-89. [PMID: 17293437 PMCID: PMC1851800 DOI: 10.1104/pp.106.092296] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2006] [Accepted: 01/31/2007] [Indexed: 05/13/2023]
Abstract
Membrane proteins within the sieve element-companion cell complex have essential roles in the physiological functioning of the phloem. The monoclonal antibody line RS6, selected from hybridomas raised against sieve elements isolated from California shield leaf (Streptanthus tortuosus; Brassicaceae) tissue cultures, recognizes an antigen in the Arabidopsis (Arabidopsis thaliana) ecotype Columbia that is associated specifically with the plasma membrane of sieve elements, but not companion cells, and accumulates at the earliest stages of sieve element differentiation. The identity of the RS6 antigen was revealed by reverse transcription-PCR of Arabidopsis leaf RNA using degenerate primers to be an early nodulin (ENOD)-like protein that is encoded by the expressed gene At3g20570. Arabidopsis ENOD-like proteins are encoded by a multigene family composed of several types of structurally related phytocyanins that have a similar overall domain structure of an amino-terminal signal peptide, plastocyanin-like copper-binding domain, proline/serine-rich domain, and carboxy-terminal hydrophobic domain. The amino- and carboxy-terminal domains of the 21.5-kD sieve element-specific ENOD are posttranslationally cleaved from the precursor protein, resulting in a mature peptide of approximately 15 kD that is attached to the sieve element plasma membrane via a carboxy-terminal glycosylphosphatidylinositol membrane anchor. Many of the Arabidopsis ENOD-like proteins accumulate in gametophytic tissues, whereas in both floral and vegetative tissues, the sieve element-specific ENOD is expressed only within the phloem. Members of the ENOD subfamily of the cupredoxin superfamily do not appear to bind copper and have unknown functions. Phenotypic analysis of homozygous T-DNA insertion mutants for the gene At3g20570 shows minimal alteration in vegetative growth but a significant reduction in the overall reproductive potential.
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Affiliation(s)
- Junaid A Khan
- Department of Applied Science, University of Arkansas, Little Rock, Arkansas 72204-1099, USA
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22
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Affiliation(s)
- Bruce Osborne
- UCD School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland (tel +35317162249; fax +35317161153; email )
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23
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Murray J, Karas B, Ross L, Brachmann A, Wagg C, Geil R, Perry J, Nowakowski K, MacGillivary M, Held M, Stougaard J, Peterson L, Parniske M, Szczyglowski K. Genetic suppressors of the Lotus japonicus har1-1 hypernodulation phenotype. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2006; 19:1082-91. [PMID: 17022172 DOI: 10.1094/mpmi-19-1082] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessive number of nodules due to genetic lesions in the HAR1 autoregulatory receptor kinase gene. In order to expand the repertoire of mutants available for the genetic dissection of the root nodule symbiosis (RNS), a screen for suppressors of the L. japonicus har1-1 hypernodulation phenotype was performed. Of 150,000 M2 plants analyzed, 61 stable L. japonicus double-mutant lines were isolated. In the context of the har1-1 mutation, 26 mutant lines were unable to form RNS, whereas the remaining 35 mutant lines carried more subtle symbiotic phenotypes, either forming white ineffective nodules or showing reduced nodulation capacity. When challenged with Glomus intraradices, 18 of the 61 suppressor lines were unable to establish a symbiosis with this arbuscular mycorrhiza fungus. Using a combined approach of genetic mapping, targeting induced local lesions in genomics, and sequencing, all non-nodulating mutant lines were characterized and shown to represent new alleles of at least nine independent symbiotic loci. The class of mutants with reduced nodulation capacity was of particular interest because some of them may specify novel plant functions that regulate nodule development in L. japonicus. To facilitate mapping of the latter class of mutants, an introgression line, in which the har1-1 allele was introduced into a polymorphic background of L. japonicus ecotype MG20, was constructed.
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Affiliation(s)
- Jeremy Murray
- Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, 1391 Sandford Street, London, Ontario N5V 4T3, Canada
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24
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Gong ZY, He ZS, Zhu JB, Yu GQ, Zou HS. Sinorhizobium meliloti nifA mutant induces different gene expression profile from wild type in Alfalfa nodules. Cell Res 2006; 16:818-29. [PMID: 17001343 DOI: 10.1038/sj.cr.7310096] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Several studies have demonstrated that the Rhizobium nifA gene is an activator of nitrogen fixation acting in nodule bacteria. To understand the effects of the Sinorhizobium meliloti nifA gene on Alfalfa, the cDNA-AFLP technique was employed to study the changes in gene expression in nifA mutant nodules. Among the approximately 3,000 transcript-derived fragments, 37 had differential expression levels. These expression levels were subsequently confirmed by reverse Northern blot and RT-polymerase chain reaction. Sequence analyses revealed that 21 cDNA fragments corresponded to genes involved in signal communication, protein degradation, nutrient metabolism, cell growth and development.
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Affiliation(s)
- Zi Ying Gong
- National Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
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25
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Liu J, Miller SS, Graham M, Bucciarelli B, Catalano CM, Sherrier DJ, Samac DA, Ivashuta S, Fedorova M, Matsumoto P, Gantt JS, Vance CP. Recruitment of novel calcium-binding proteins for root nodule symbiosis in Medicago truncatula. PLANT PHYSIOLOGY 2006; 141:167-77. [PMID: 16543412 PMCID: PMC1459311 DOI: 10.1104/pp.106.076711] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2006] [Revised: 01/12/2006] [Accepted: 02/16/2006] [Indexed: 05/07/2023]
Abstract
Legume rhizobia symbiotic nitrogen (N2) fixation plays a critical role in sustainable nitrogen management in agriculture and in the Earth's nitrogen cycle. Signaling between rhizobia and legumes initiates development of a unique plant organ, the root nodule, where bacteria undergo endocytosis and become surrounded by a plant membrane to form a symbiosome. Between this membrane and the encased bacteria exists a matrix-filled space (the symbiosome space) that is thought to contain a mixture of plant- and bacteria-derived proteins. Maintenance of the symbiosis state requires continuous communication between the plant and bacterial partners. Here, we show in the model legume Medicago truncatula that a novel family of six calmodulin-like proteins (CaMLs), expressed specifically in root nodules, are localized within the symbiosome space. All six nodule-specific CaML genes are clustered in the M. truncatula genome, along with two other nodule-specific genes, nodulin-22 and nodulin-25. Sequence comparisons and phylogenetic analysis suggest that an unequal recombination event occurred between nodulin-25 and a nearby calmodulin, which gave rise to the first CaML, and the gene family evolved by tandem duplication and divergence. The data provide striking evidence for the recruitment of a ubiquitous Ca(2+)-binding gene for symbiotic purposes.
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Affiliation(s)
- Junqi Liu
- Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55108, USA
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26
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Silverstein KAT, Graham MA, VandenBosch KA. Novel paralogous gene families with potential function in legume nodules and seeds. CURRENT OPINION IN PLANT BIOLOGY 2006; 9:142-6. [PMID: 16459131 DOI: 10.1016/j.pbi.2006.01.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Accepted: 01/20/2006] [Indexed: 05/06/2023]
Abstract
Within the plant kingdom, legumes are unusual in their ability to form nitrogen-fixing nodules in symbiosis with certain bacteria in the family Rhizobiaceae (rhizhobia). Genes that are required for signaling between plant and symbiont, and for the development and maintenance of the nodule, were either created de novo or adopted from other plant pathways. Only in recent years have genome-scale sequence data from legumes made it possible to identify large, novel families of genes probably evolved to function in nodulation. Members of these novel families are expressed in seeds or nodules, and are homologous to defense-related proteins. Perhaps the most striking example is a large family (of more than 340 members) of cysteine cluster proteins that have homology to plant defensins.
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Affiliation(s)
- Kevin A T Silverstein
- Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108, USA
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27
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Zhu H, Riely BK, Burns NJ, Ané JM. Tracing nonlegume orthologs of legume genes required for nodulation and arbuscular mycorrhizal symbioses. Genetics 2006; 172:2491-9. [PMID: 16452143 PMCID: PMC1456400 DOI: 10.1534/genetics.105.051185] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Accepted: 01/24/2006] [Indexed: 01/31/2023] Open
Abstract
Most land plants can form a root symbiosis with arbuscular mycorrhizal (AM) fungi for assimilation of inorganic phosphate from the soil. In contrast, the nitrogen-fixing root nodule symbiosis is almost completely restricted to the legumes. The finding that the two symbioses share common signaling components in legumes suggests that the evolutionarily younger nitrogen-fixing symbiosis has recruited functions from the more ancient AM symbiosis. The recent advances in cloning of the genes required for nodulation and AM symbioses from the two model legumes, Medicago truncatula and Lotus japonicus, provide a unique opportunity to address biological questions pertaining to the evolution of root symbioses in plants. Here, we report that nearly all cloned legume genes required for nodulation and AM symbioses have their putative orthologs in nonlegumes. The orthologous relationship can be clearly defined on the basis of both sequence similarity and microsyntenic relationship. The results presented here serve as a prelude to the comparative analysis of orthologous gene function between legumes and nonlegumes and facilitate our understanding of how gene functions and signaling pathways have evolved to generate species- or family-specific phenotypes.
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Affiliation(s)
- Hongyan Zhu
- Department of Plant and Soil Sciences, University of Kentucky, Lexington 40546, USA.
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28
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Lievens S, Goormachtig S, Den Herder J, Capoen W, Mathis R, Hedden P, Holsters M. Gibberellins are involved in nodulation of Sesbania rostrata. PLANT PHYSIOLOGY 2005; 139:1366-79. [PMID: 16258018 PMCID: PMC1283772 DOI: 10.1104/pp.105.066944] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Upon submergence, Azorhizobium caulinodans infects the semiaquatic legume Sesbania rostrata via the intercellular crack entry process, resulting in lateral root-based nodules. A gene encoding a gibberellin (GA) 20-oxidase, SrGA20ox1, involved in GA biosynthesis, was transiently up-regulated during lateral root base nodulation. Two SrGA20ox1 expression patterns were identified, one related to intercellular infection and a second observed in nodule meristem descendants. The infection-related expression pattern depended on bacterially produced nodulation (Nod) factors. Pharmacological studies demonstrated that GAs were involved in infection pocket and infection thread formation, two Nod factor-dependent events that initiate lateral root base nodulation, and that they were also needed for nodule primordium development. Moreover, GAs inhibited the root hair curling process. These results show that GAs are Nod factor downstream signals for nodulation in hydroponic growth.
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Affiliation(s)
- Sam Lievens
- Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, B-9052 Gent, Belgium
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29
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Takeda N, Okamoto S, Hayashi M, Murooka Y. Expression of LjENOD40 genes in response to symbiotic and non-symbiotic signals: LjENOD40-1 and LjENOD40-2 are differentially regulated in Lotus japonicus. PLANT & CELL PHYSIOLOGY 2005; 46:1291-8. [PMID: 15937327 DOI: 10.1093/pcp/pci138] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Nitrogen fixation in nodules provides leguminous plants with an ability to grow in nitrogen-starved soil. Infection of the host plants by microsymbionts triggers various physiological and morphological changes during nodule formation. In Lotus japonicus, expression of early nodulin (ENOD) genes is triggered by perception of bacterial signal molecules, nodulation factors (Nod factors). We examined the expression patterns of ENOD40 genes during the nodule formation process. Two ENOD40 genes of L. japonicus were specifically expressed in the nodule formation process, but they showed different expression patterns upon infection. Each ENOD40 gene demonstrates an individual specificity and regulation with regard to rhizobial infection.
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Affiliation(s)
- Naoya Takeda
- Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871 Japan
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30
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Bright LJ, Liang Y, Mitchell DM, Harris JM. The LATD gene of Medicago truncatula is required for both nodule and root development. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2005; 18:521-32. [PMID: 15986921 DOI: 10.1094/mpmi-18-0521] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The evolutionary origins of legume root nodules are largely unknown. We have identified a gene, LATD, of the model legume Medicago truncatula, that is required for both nodule and root development, suggesting that these two developmental processes may share a common evolutionary origin. The latd mutant plants initiate nodule formation but do not complete it, resulting in immature, non-nitrogen-fixing nodules. Similarly, lateral roots initiate, but remain short stumps. The primary root, which initially appears to be wild type, gradually ceases growth and forms an abnormal tip that resembles that of the mutant lateral roots. Infection by the rhizobial partner, Sinorhizobium meliloti, can occur, although infection is rarely completed. Once inside latd mutant nodules, S. meliloti fails to express rhizobial genes associated with the developmental transition from free-living bacterium to endosymbiont, such as bacA and nex38. The infecting rhizobia also fail to express nifH and fix nitrogen. Thus, both plant and bacterial development are blocked in latd mutant roots. Based on the latd mutant phenotype, we propose that the wild-type function of the LATD gene is to maintain root meristems. The strong requirement of both nodules and lateral roots for wild-type LATD gene function supports lateral roots as a possible evolutionary origin for legume nodules.
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Affiliation(s)
- Lydia J Bright
- Department of Botany and Agricultural Biochemistry, University of Vermont, Burlington 05405-0086, USA
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31
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Ooki Y, Banba M, Yano K, Maruya J, Sato S, Tabata S, Saeki K, Hayashi M, Kawaguchi M, Izui K, Hata S. Characterization of the Lotus japonicus symbiotic mutant lot1 that shows a reduced nodule number and distorted trichomes. PLANT PHYSIOLOGY 2005; 137:1261-71. [PMID: 15793069 PMCID: PMC1088319 DOI: 10.1104/pp.104.056630] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2004] [Revised: 01/17/2005] [Accepted: 01/31/2005] [Indexed: 05/18/2023]
Abstract
We isolated a recessive symbiotic mutant of Lotus japonicus that defines a genetic locus, LOT1 (for low nodulation and trichome distortion). The nodule number per plant of the mutant was about one-fifth of that of the wild type. The lot1 mutant showed a moderate dwarf phenotype and distorted trichomes, but its root hairs showed no apparent differences to those of the wild type. Infection thread formation after inoculation of Mesorhizobium loti was repressed in lot1 compared to that in the wild type. The nodule primordia of lot1 did not result in any aborted nodule-like structure, all nodules becoming mature and exhibiting high nitrogen fixation activity. The mutant was normally colonized by mycorrhizal fungi. lot1 also showed higher sensitivity to nitrate than the wild type. The grown-up seedlings of lot1 were insensitive to any ethylene treatments with regard to nodulation, although the mutant showed normal triple response on germination. It is conceivable that a nodulation-specific ethylene signaling pathway is constitutively activated in the mutant. Grafting experiments with lot1 and wild-type seedlings suggested that the root genotype mainly determines the low nodulation phenotype of the mutant, while the trichome distortion is regulated by the shoot genotype. Grafting of har1-4 shoots to lot1 roots resulted in an intermediate nodule number, i.e. more than that of lot1 and less than that of har1-4. Putative double mutants of lot1 and har1 also showed intermediate nodulation. Thus, it was indicated that LOT1 is involved in a distinct signal transduction pathway independent of HAR1.
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Affiliation(s)
- Yasuhiro Ooki
- Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
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32
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Karas B, Murray J, Gorzelak M, Smith A, Sato S, Tabata S, Szczyglowski K. Invasion of Lotus japonicus root hairless 1 by Mesorhizobium loti involves the nodulation factor-dependent induction of root hairs. PLANT PHYSIOLOGY 2005; 137:1331-44. [PMID: 15778455 PMCID: PMC1088324 DOI: 10.1104/pp.104.057513] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2004] [Revised: 01/11/2005] [Accepted: 01/17/2005] [Indexed: 05/18/2023]
Abstract
In many legumes, including Lotus japonicus and Medicago truncatula, susceptible root hairs are the primary sites for the initial signal perception and physical contact between the host plant and the compatible nitrogen-fixing bacteria that leads to the initiation of root invasion and nodule organogenesis. However, diverse mechanisms of nodulation have been described in a variety of legume species that do not rely on root hairs. To clarify the significance of root hairs during the L. japonicus-Mesorhizobium loti symbiosis, we have isolated and performed a detailed analysis of four independent L. japonicus root hair developmental mutants. We show that although important for the efficient colonization of roots, the presence of wild-type root hairs is not required for the initiation of nodule primordia (NP) organogenesis and the colonization of the nodule structures. In the genetic background of the L. japonicus root hairless 1 mutant, the nodulation factor-dependent formation of NP provides the structural basis for alternative modes of invasion by M. loti. Surprisingly, one mode of root colonization involves nodulation factor-dependent induction of NP-associated cortical root hairs and epidermal root hairs, which, in turn, support bacterial invasion. In addition, entry of M. loti through cracks at the cortical surface of the NP is described. These novel mechanisms of nodule colonization by M. loti explain the fully functional, albeit significantly delayed, nodulation phenotype of the L. japonicus ROOT HAIRLESS mutant.
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Affiliation(s)
- Bogumil Karas
- Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London, Ontario, N5V 4T3, Canada
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Zhu H, Choi HK, Cook DR, Shoemaker RC. Bridging model and crop legumes through comparative genomics. PLANT PHYSIOLOGY 2005; 137:1189-96. [PMID: 15824281 PMCID: PMC1088312 DOI: 10.1104/pp.104.058891] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2004] [Revised: 01/18/2005] [Accepted: 01/24/2005] [Indexed: 05/18/2023]
Affiliation(s)
- Hongyan Zhu
- Department of Plant and Soil Sciences, University of Kentucky, Lexington, Kentucky 40546, USA.
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Rodríguez-Llorente ID, Pérez-Hormaeche J, El Mounadi K, Dary M, Caviedes MA, Cosson V, Kondorosi A, Ratet P, Palomares AJ. From pollen tubes to infection threads: recruitment of Medicago floral pectic genes for symbiosis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 39:587-98. [PMID: 15272876 DOI: 10.1111/j.1365-313x.2004.02155.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
While the biology of nitrogen-fixing root nodules has been extensively studied, little is known about the evolutionary events that predisposed legume plants to form symbiosis with rhizobia. We have studied the presence and the expression of two pectic gene families in Medicago, polygalacturonases (PGs) and pectin methyl esterases (PMEs) during the early steps of the Sinorhizobium meliloti-Medicago interaction and compared them with related pollen-specific genes. First, we have compared the expression of MsPG3, a PG gene specifically expressed during the symbiotic interaction, with the expression of MsPG11, a highly homologous pollen-specific gene, using promoter-gus fusions in transgenic M. truncatula and tobacco plants. These results demonstrated that the symbiotic promoter functions as a pollen-specific promoter in the non-legume host. Second, we have identified the presence of a gene family of at least eight differentially expressed PMEs in Medicago. One subfamily is represented by one symbiotic gene (MtPER) and two pollen-expressed genes (MtPEF1 and MtPEF2) that are clustered in the M. truncatula genome. The promoter-gus studies presented in this work and the homology between plant PGs, together with the analysis of the PME locus structure and MtPER expression studies, suggest that the symbiotic MsPG3 and MtPER could have as ancestors pollen-expressed genes involved in polar tip growth processes during pollen tube elongation. Moreover, they could have been recruited after gene duplication in the symbiotic interaction to facilitate polar tip growth during infection thread formation.
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Affiliation(s)
- Ignacio D Rodríguez-Llorente
- Departamento de Microbiología y Parasitología, Facultad de Farmacia, Universidad de Sevilla, 41012 Sevilla, Spain
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35
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Graham MA, Silverstein KAT, Cannon SB, VandenBosch KA. Computational identification and characterization of novel genes from legumes. PLANT PHYSIOLOGY 2004; 135:1179-97. [PMID: 15266052 PMCID: PMC519039 DOI: 10.1104/pp.104.037531] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2003] [Revised: 04/01/2004] [Accepted: 04/03/2004] [Indexed: 05/18/2023]
Abstract
The Fabaceae, the third largest family of plants and the source of many crops, has been the target of many genomic studies. Currently, only the grasses surpass the legumes for the number of publicly available expressed sequence tags (ESTs). The quantity of sequences from diverse plants enables the use of computational approaches to identify novel genes in specific taxa. We used BLAST algorithms to compare unigene sets from Medicago truncatula, Lotus japonicus, and soybean (Glycine max and Glycine soja) to nonlegume unigene sets, to GenBank's nonredundant and EST databases, and to the genomic sequences of rice (Oryza sativa) and Arabidopsis. As a working definition, putatively legume-specific genes had no sequence homology, below a specified threshold, to publicly available sequences of nonlegumes. Using this approach, 2,525 legume-specific EST contigs were identified, of which less than three percent had clear homology to previously characterized legume genes. As a first step toward predicting function, related sequences were clustered to build motifs that could be searched against protein databases. Three families of interest were more deeply characterized: F-box related proteins, Pro-rich proteins, and Cys cluster proteins (CCPs). Of particular interest were the >300 CCPs, primarily from nodules or seeds, with predicted similarity to defensins. Motif searching also identified several previously unknown CCP-like open reading frames in Arabidopsis. Evolutionary analyses of the genomic sequences of several CCPs in M. truncatula suggest that this family has evolved by local duplications and divergent selection.
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Affiliation(s)
- Michelle A Graham
- Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108, USA
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36
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Calonje M, Cubas P, Martínez-Zapater JM, Carmona MJ. Floral meristem identity genes are expressed during tendril development in grapevine. PLANT PHYSIOLOGY 2004; 135:1491-501. [PMID: 15247405 PMCID: PMC519065 DOI: 10.1104/pp.104.040832] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2004] [Revised: 04/21/2004] [Accepted: 04/26/2004] [Indexed: 05/19/2023]
Abstract
To study the early steps of flower initiation and development in grapevine (Vitis vinifera), we have isolated two MADS-box genes, VFUL-L and VAP1, the putative FUL-like and AP1 grapevine orthologs, and analyzed their expression patterns during vegetative and reproductive development. Both genes are expressed in lateral meristems that, in grapevine, can give rise to either inflorescences or tendrils. They are also coexpressed in inflorescence and flower meristems. During flower development, VFUL-L transcripts are restricted to the central part of young flower meristems and, later, to the prospective carpel-forming region, which is consistent with a role of this gene in floral transition and carpel and fruit development. Expression pattern of VAP1 suggests that it may play a role in flowering transition and flower development. However, its lack of expression in sepal primordia, does not support its role as an A-function gene in grapevine. Neither VFUL-L nor VAP1 expression was detected in vegetative organs such as leaves or roots. In contrast, they are expressed throughout tendril development. Transcription of both genes in tendrils of very young plants that have not undergone flowering transition indicates that this expression is independent of the flowering process. These unique expression patterns of genes typically involved in reproductive development have implications on our understanding of flower induction and initiation in grapevine, on the origin of grapevine tendrils and on the functional roles of AP1-and FUL-like genes in plant development. These results also provide molecular support to the hypothesis that Vitis tendrils are modified reproductive organs adapted to climb.
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Affiliation(s)
- Myriam Calonje
- Departamento de Biotecnología, Escuela Técnica Superior Ingenieros Agrónomos, Universidad Politécnica de Madrid, 28040 Madrid, Spain
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Brewin NJ. Plant Cell Wall Remodelling in the Rhizobium–Legume Symbiosis. CRITICAL REVIEWS IN PLANT SCIENCES 2004; 23:293-316. [PMID: 0 DOI: 10.1080/07352680490480734] [Citation(s) in RCA: 164] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
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Tansengco ML, Imaizumi-Anraku H, Yoshikawa M, Takagi S, Kawaguchi M, Hayashi M, Murooka Y. Pollen Development and Tube Growth are Affected in the Symbiotic Mutant of Lotus japonicus, crinkle. ACTA ACUST UNITED AC 2004; 45:511-20. [PMID: 15169932 DOI: 10.1093/pcp/pch076] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The symbiotic mutant of Lotus japonicus, crinkle (crk), exhibits abnormal nodulation and other alterations in the root hairs, trichomes, and seedpods. Defective nodulation in crk mutant is due to the arrested infection thread growth from the epidermis into the cortex. Here, we describe that crk is also affected in male fertility that causes the production of small pods with few seeds. Under in vitro conditions, pollen germination and tube growth were markedly reduced in the crk mutant. A swollen tip phenotype with disorganized filamentous actin (F-actin) was observed in the mutant pollen tubes after prolonged in vitro culture. During pollen development, the striking difference noted in the mutant was the small size of the microspores that remained spherical. Histological examination of ovule development, as well as outcrosses of the mutant as female to wild type as male, showed no evidence of abnormality in the female gametophyte development. Based on these findings, the Crk gene, aside from its role in the infection process during nodulation, is also involved in male gametophyte development and function. Therefore, this gene represents a connection between nodule symbiosis, polar tip growth, and other plant developmental processes.
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Affiliation(s)
- Myra L Tansengco
- Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka, 565-0871 Japan
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Radutoiu S, Madsen LH, Madsen EB, Felle HH, Umehara Y, Grønlund M, Sato S, Nakamura Y, Tabata S, Sandal N, Stougaard J. Plant recognition of symbiotic bacteria requires two LysM receptor-like kinases. Nature 2003; 425:585-92. [PMID: 14534578 DOI: 10.1038/nature02039] [Citation(s) in RCA: 704] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2003] [Accepted: 09/11/2003] [Indexed: 11/09/2022]
Abstract
Although most higher plants establish a symbiosis with arbuscular mycorrhizal fungi, symbiotic nitrogen fixation with rhizobia is a salient feature of legumes. Despite this host range difference, mycorrhizal and rhizobial invasion shares a common plant-specified genetic programme controlling the early host interaction. One feature distinguishing legumes is their ability to perceive rhizobial-specific signal molecules. We describe here two LysM-type serine/threonine receptor kinase genes, NFR1 and NFR5, enabling the model legume Lotus japonicus to recognize its bacterial microsymbiont Mesorhizobium loti. The extracellular domains of the two transmembrane kinases resemble LysM domains of peptidoglycan- and chitin-binding proteins, suggesting that they may be involved directly in perception of the rhizobial lipochitin-oligosaccharide signal. We show that NFR1 and NFR5 are required for the earliest physiological and cellular responses to this lipochitin-oligosaccharide signal, and demonstrate their role in the mechanism establishing susceptibility of the legume root for bacterial infection.
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Affiliation(s)
- Simona Radutoiu
- Laboratory of Gene Expression, Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10, 8000 Aarhus C, Denmark
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Beveridge CA, Weller JL, Singer SR, Hofer JMI. Axillary meristem development. Budding relationships between networks controlling flowering, branching, and photoperiod responsiveness. PLANT PHYSIOLOGY 2003; 131:927-34. [PMID: 12644645 PMCID: PMC1540292 DOI: 10.1104/pp.102.017525] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Affiliation(s)
- Christine A Beveridge
- Australian Research Council Centre of Excellence for Integrative Legume Research, The University of Queensland, St Lucia, Brisbane.
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41
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Penmetsa RV, Frugoli JA, Smith LS, Long SR, Cook DR. Dual genetic pathways controlling nodule number in Medicago truncatula. PLANT PHYSIOLOGY 2003; 131:998-1008. [PMID: 12644652 PMCID: PMC166865 DOI: 10.1104/pp.015677] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2002] [Revised: 11/11/2002] [Accepted: 12/12/2002] [Indexed: 05/17/2023]
Abstract
We report the isolation and characterization of a new Medicago truncatula hyper-nodulation mutant, designated sunn (super numeric nodules). Similar to the previously described ethylene-insensitive mutant sickle, sunn exhibits a 10-fold increase in the number of nodules within the primary nodulation zone. Despite this general similarity, these two mutants are readily distinguished based on anatomical, genetic, physiological, and molecular criteria. In contrast to sickle, where insensitivity to ethylene is thought to be causal to the hyper-nodulation phenotype (R.V. Penmetsa, D.R. Cook [1997] Science 275: 527-530), nodulation in sunn is normally sensitive to ethylene. Nevertheless, sunn exhibits seedling root growth that is insensitive to ethylene, although other aspects of the ethylene triple response are normal; these observations suggest that hormonal responses might condition the sunn phenotype in a manner distinct from sickle. The two mutants also differ in the anatomy of the nodulation zone: Successful infection and nodule development in sunn occur predominantly opposite xylem poles, similar to wild type. In sickle, however, both infection and nodulation occur randomly throughout the circumference of the developing root. Genetic analysis indicates that sunn and sickle correspond to separate and unlinked loci, whereas the sunn/skl double mutant exhibits a novel and additive super-nodulation phenotype. Taken together, these results suggest a working hypothesis wherein sunn and sickle define distinct genetic pathways, with skl regulating the number and distribution of successful infection events, and sunn regulating nodule organogenesis.
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Affiliation(s)
- R Varma Penmetsa
- Department of Biological Sciences, Stanford University, Stanford, California 94305, USA
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Penmetsa RV, Frugoli JA, Smith LS, Long SR, Cook DR. Dual genetic pathways controlling nodule number in Medicago truncatula. PLANT PHYSIOLOGY 2003. [PMID: 12644652 DOI: 10.1104/pp.900061] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We report the isolation and characterization of a new Medicago truncatula hyper-nodulation mutant, designated sunn (super numeric nodules). Similar to the previously described ethylene-insensitive mutant sickle, sunn exhibits a 10-fold increase in the number of nodules within the primary nodulation zone. Despite this general similarity, these two mutants are readily distinguished based on anatomical, genetic, physiological, and molecular criteria. In contrast to sickle, where insensitivity to ethylene is thought to be causal to the hyper-nodulation phenotype (R.V. Penmetsa, D.R. Cook [1997] Science 275: 527-530), nodulation in sunn is normally sensitive to ethylene. Nevertheless, sunn exhibits seedling root growth that is insensitive to ethylene, although other aspects of the ethylene triple response are normal; these observations suggest that hormonal responses might condition the sunn phenotype in a manner distinct from sickle. The two mutants also differ in the anatomy of the nodulation zone: Successful infection and nodule development in sunn occur predominantly opposite xylem poles, similar to wild type. In sickle, however, both infection and nodulation occur randomly throughout the circumference of the developing root. Genetic analysis indicates that sunn and sickle correspond to separate and unlinked loci, whereas the sunn/skl double mutant exhibits a novel and additive super-nodulation phenotype. Taken together, these results suggest a working hypothesis wherein sunn and sickle define distinct genetic pathways, with skl regulating the number and distribution of successful infection events, and sunn regulating nodule organogenesis.
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Affiliation(s)
- R Varma Penmetsa
- Department of Biological Sciences, Stanford University, Stanford, California 94305, USA
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