Antagonistic interaction between jasmonic acid and cytokinin in xylem development

Coordination and regulation of vascular development in roots

Vascular tissue is crucial for the transport of substances and physical support in most plants. Vascular development in roots encompasses cell proliferation, pattern formation, cell specification, and differentiation. In the roots, the positions and timing of cell proliferation and the differentiation of xylem and phloem cells are strictly controlled in order to achieve continuous vascular transport. This review describes recent advances in our understanding of the molecular mechanisms of vascular development, with a particular focus on the modulators of each of the above aspects in Arabidopsis roots. In particular, recent technological advances such as genome editing technology and single-cell analysis have led to the discovery of important genes that control vascular development. This paper shows that factors such as hormones, peptides, transcription factors, and microRNAs interact in a multilayered manner to modulate key regulators of root vascular development, ensuring stable vascular formation.

A review of the interaction mechanisms between jasmonic acid (JA) and various plant hormones, as well as the core regulatory role of MYC2

Jasmonic acid (JA), as a defensive plant hormone, can synergistically or antagonistically interact with common hormones such as gibberellin (GA), abscisic acid (ABA), indole-3-acetic hormone acid (IAA), and ethylene (ETH) during the plant growth process, as well as interact with hormones such as melatonin (MT), brassinolide (BR), and resveratrol to regulate plant growth and development processes such as metabolite synthesis, pest and disease defense, and organ growth. The core regulatory factor MYC2 of JA mainly mediates the signal transduction pathways of these hormone interactions by interacting with other genes or regulating transcription. This article reviews the mechanism of cross-talk between JA and hormones such as ABA, GA, and salicylic acid (SA), and discusses the role of MYC2 in hormone interactions.

SlASR3 mediates crosstalk between auxin and jasmonic acid signaling to regulate trichome formation in tomato

Trichomes play a pivotal role in plant resistance to biotic and abiotic stresses. Both auxin and jasmonic acid (JA) could induce tomato type II, V, and VI trichome formation. However, the existence of crosstalk between auxin and JA in trichome formation is not yet fully elucidated. In this study, we identified a Trihelix/MYB-like gene, SlASR3, is inhibited by both auxin and JA and is expressed in type II and VI trichomes in tomatoes. Knock-down or knockout of SlASR3 increased the densities of type II and VI trichomes, whereas overexpression of SlASR3 reduced the densities of type II and VI trichomes. SlASR3 was involved in the indole acetic acid (IAA)- and JA-induced formation of these trichome types. SlARF4 negatively regulated the transcription of SlASR3, and its effect on IAA-induced trichome formation depended on SlASR3. Likewise, SlMYC1 negatively regulated the transcription of SlASR3, and the regulation of SlMYC1 on JA-induced trichome formation was also SlASR3-dependent. Knock-down or knockout of SlASR3 increased the resistance to two-spotted spider mites in tomatoes. The research findings demonstrate that SlASR3 acts as a mediator in the crosstalk between JA and auxin signaling to regulate trichome formation and provide a new candidate gene for enhancing resistance to two-spotted spider mites.

Dressed Up to the Nines: The Interplay of Phytohormones Signaling and Redox Metabolism During Plant Response to Drought

Plants must effectively respond to various environmental stimuli to achieve optimal growth. This is especially relevant in the context of climate change, where drought emerges as a major factor globally impacting crops and limiting overall yield potential. Throughout evolution, plants have developed adaptative strategies for environmental stimuli, with plant hormones and reactive oxygen species (ROS) playing essential roles in their development. Hormonal signaling and the maintenance of ROS homeostasis are interconnected, playing indispensable roles in growth, development, and stress responses and orchestrating diverse molecular responses during environmental adversities. Nine principal classes of phytohormones have been categorized: auxins, brassinosteroids, cytokinins, and gibberellins primarily oversee developmental growth regulation, while abscisic acid, ethylene, jasmonic acid, salicylic acid, and strigolactones are the main orchestrators of environmental stress responses. Coordination between phytohormones and transcriptional regulation is crucial for effective plant responses, especially in drought stress. Understanding the interplay of ROS and phytohormones is pivotal for elucidating the molecular mechanisms involved in plant stress responses. This review provides an overview of the intricate relationship between ROS, redox metabolism, and the nine different phytohormones signaling in plants, shedding light on potential strategies for enhancing drought tolerance for sustainable crop production.

RhMYC2 controls petal size through synergistic regulation of jasmonic acid and cytokinin signaling in rose

Petal size is determined by cell division and cell expansion. Jasmonic acid (JA) has been reported to be associated with floral development, but its regulatory mechanism affecting petal size remains unclear. Here, we reveal the vital role of JA in regulating petal size and the duration of the cell division phase via the key JA signaling component RhMYC2. We show that RhMYC2 expression is induced by exogenous treatment with methyl jasmonate and decreases from stage 0 to stage 2 of flower organ development, corresponding to the cell division phase. Furthermore, silencing RhMYC2 shortened the duration of the cell division phase, ultimately accelerating flowering opening and resulting in smaller petals. In addition, we determined that RhMYC2 controls cytokinin homeostasis in rose petals by directly activating the expression of the cytokinin biosynthetic gene LONELY GUY3 (RhLOG3) and repressing that of the cytokinin catabolism gene CYTOKININ OXIDASE/DEHYDROGENASE6 (RhCKX6). Silencing RhLOG3 shortened the duration of the cell division period and produced smaller petals, similar to RhMYC2 silencing. Our results underscore the synergistic effects of JA and cytokinin in regulating floral development, especially for petal size in roses.

Adaptive roles of cytokinins in enhancing plant resilience and yield against environmental stressors

Innovative agricultural strategies are essential for addressing the urgent challenge of food security in light of climate change, population growth, and various environmental stressors. Cytokinins (CKs) play a pivotal role in enhancing plant resilience and productivity. These compounds, which include isoprenoid and aromatic types, are synthesized through pathways involving key enzymes such as isopentenyl transferase and cytokinin oxidase. Under abiotic stress conditions, CKs regulate critical physiological processes by improving photosynthetic efficiency, enhancing antioxidant enzyme activity, and optimizing root architecture. They also reduce the levels of reactive oxygen species and malondialdehyde, resulting in improved plant performance and yield. CKs interact intricately with other phytohormones, including abscisic acid, ethylene, salicylic acid, and jasmonic acid, to modulate stress-responsive pathways. This hormonal cross-talk is vital for finely tuning plant responses to stress. Additionally, CKs influence nutrient uptake and enhance responses to heavy metal stress, thereby bolstering overall plant resilience. The application of CKs helps plants maintain higher chlorophyll levels, boost antioxidant systems, and promote root and shoot growth. The strategic utilization of CKs presents an adaptive approach for developing robust crops capable of withstanding diverse environmental stressors, thus contributing to sustainable agricultural practices and global food security. Ongoing research into the mechanisms of CK action and their interactions with other hormones is essential for maximizing their agricultural potential. This underscores the necessity for continued innovation and research in agricultural practices, in alignment with global goals of sustainable productivity and food security.

Advances in functional studies of plant MYC transcription factors

Myelocytomatosis (MYC) transcription factors (TFs) belong to the basic helix-loop-helix (bHLH) family in plants and play a central role in governing a wide range of physiological processes. These processes encompass plant growth, development, adaptation to biotic and abiotic stresses, as well as secondary metabolism. In recent decades, significant strides have been made in comprehending the multifaceted regulatory functions of MYCs. This advancement has been achieved through the cloning of MYCs and the characterization of plants with MYC deficiencies or overexpression, employing comprehensive genome-wide 'omics' and protein-protein interaction technologies. MYCs act as pivotal components in integrating signals from various phytohormones' transcriptional regulators to orchestrate genome-wide transcriptional reprogramming. In this review, we have compiled current research on the role of MYCs as molecular switches that modulate signal transduction pathways mediated by phytohormones and phytochromes. This comprehensive overview allows us to address lingering questions regarding the interplay of signals in response to environmental cues and developmental shift. It also sheds light on the potential implications for enhancing plant resistance to diverse biotic and abiotic stresses through genetic improvements achieved by plant breeding and synthetic biology efforts.

Hormonal control of the molecular networks guiding vascular tissue development in the primary root meristem of Arabidopsis

Vascular tissues serve a dual function in plants, both providing physical support and controlling the transport of nutrients, water, hormones, and other small signaling molecules. Xylem tissues transport water from root to shoot; phloem tissues transfer photosynthates from shoot to root; while divisions of the (pro)cambium increase the number of xylem and phloem cells. Although vascular development constitutes a continuous process from primary growth in the early embryo and meristem regions to secondary growth in the mature plant organs, it can be artificially separated into distinct processes including cell type specification, proliferation, patterning, and differentiation. In this review, we focus on how hormonal signals orchestrate the molecular regulation of vascular development in the Arabidopsis primary root meristem. Although auxin and cytokinin have taken center stage in this aspect since their discovery, other hormones including brassinosteroids, abscisic acid, and jasmonic acid also take leading roles during vascular development. All these hormonal cues synergistically or antagonistically participate in the development of vascular tissues, forming a complex hormonal control network.

Comparative Transcriptome Sequencing and Endogenous Phytohormone Content of Annual Grafted Branches of Zelkova schneideriana and Its Dwarf Variety HenTianGao

Zelkova schneideriana is a fast-growing tree species endemic to China. Recent surveys and reports have highlighted a continued decline in its natural populations; therefore, it is included in the Red List of Threatened Species by The International Union for Conservation of Nature. A new variety "HenTianGao" (H) has been developed with smaller plant height, slow growth, and lower branching points. In this study, we attempted to understand the differences in plant height of Z. schneideriana (J) and its dwarf variety H. We determined the endogenous hormone content in the annual grafted branches of both J and H. J exhibited higher gibberellic acid (GA)-19 and trans-Zeatin (tZ) levels, whereas H had higher levels of indole-3-acetic acid (IAA) catabolite 2-oxindole-3-acetic acid (OxIAA), IAA-Glu conjugate, and jasmonic acid (JA) (and its conjugate JA-Ile). The transcriptome comparison showed differential regulation of 20,944 genes enriched in growth and development, signaling, and metabolism-related pathways. The results show that the differential phytohormone level (IAA, JA, tZ, and GA) was consistent with the expression of the genes associated with their biosynthesis. The differences in relative OxIAA, IAA-Glu, GA19, trans-Zeatin, JA, and JA-Ile levels were linked to changes in respective signaling-related genes. We also observed significant differences in the expression of cell size, number, proliferation, cell wall biosynthesis, and remodeling-related genes in J and H. The differences in relative endogenous hormone levels, expression of biosynthesis, and signaling genes provide a theoretical basis for understanding the plant height differences in Z. schneideriana.

Jasmonic Acid Effect on Cucumis sativus L. Growth Is Related to Inhibition of Plasma Membrane Proton Pump and the Uptake and Assimilation of Nitrates

When plants are exposed to environmental stress, their growth is inhibited. Under such conditions, controlled inhibition of growth is beneficial for plant survival. Jasmonic acid (JA) is a well-known phytohormone that limits plant growth, which has been confirmed in several species. However, its role in cucumber seedlings has not yet been comprehensively investigated. For this reason, we aimed to determine the involvement of JA in the regulation of proteins crucial for growth including plasma membrane proton pump (PM H+-ATPase), PM nitrate transporters, and nitrate reductase (NR). Treatment of cucumber seedlings with JA not only limited their growth but also increased the H2O2 content in their roots. The main sources of ROS generated for signalling purposes are PM NADPH oxidase (RBOH) and superoxide dismutase (SOD). Exposure of seedlings to JA induced the expression of some CsRBOH and SOD encoding genes, suggesting that ROS signalling can be activated by JA. As a consequence of JA exposure, the activity of all analysed proteins was inhibited and the expression of their genes was modified. The results indicate that reduction of PM H+-ATPase activity and the related decrease in nitrate uptake and assimilation are responsible for the root growth retardation of JA-treated plants.

Exogenous methyl jasmonate and cytokinin antagonistically regulate lignin biosynthesis by mediating CsHCT expression in Camellia sinensis

Tea plant, an important beverage crop, is cultivated worldwide. Lignification can improve the hardness of tea plant, which is of great significance for tea quality. Jasmonates (JAs) and cytokinin are plant hormones that control processes of plant development and secondary metabolite accumulation. Hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (HCT) is primarily involved in lignin biosynthesis. The effects of exogenous application of JAs and cytokinin on lignin biosynthesis and related HCT gene expression profiles in tea plants are still unclear. In order to investigate the effects of exogenous JAs and cytokinin on lignin accumulation, anatomical structures, and CsHCT gene profiles in tea plants, we treated tea plants with methyl jasmonate (MeJA) and cytokinin (6-BA). MeJA and 6-BA treatments triggered the lignification at 6 and 12 d in tea leaves. The combined treatment resulted in an increase in lignin content at 6 d, which was 1.32 times of that at 0 d for 'Mengshan 9.' The CsHCTs in clade 2 (CsHCT5, CsHCT6, CsHCT7, and CsHCT8) were mainly expressed in leaves. We found that exogenous MeJA and cytokinin might be able to antagonistically regulate tea plant lignin accumulation through the mediation of CsHCT expression. This study revealed that HCTs play potential important roles involved in lignin biosynthesis of tea plant development and hormonal stimuli.

Chitosan fabricated biogenic silver nanoparticles (Ch@BSNP) protectively modulate the defense mechanism of tomato during bacterial leaf spot (BLS) disease

Herein, the impact of chitosan fabricated biogenic silver nanoparticles (Ch@BSNP) has been evaluated for the protective management of bacterial leaf spot (BLS) disease in tomatoes caused by Xanthomonas campestris (NCIM5028). The Ch@BSNP originated by the Trichoderma viride (MTCC5661) derived extracellular compounds and subsequent chitosan hybridization. Spherical-shaped Ch@BSNP (30-35 nm) treated diseased plants were able to combat the biotic stress, as evidenced by the decreased elevated response of stress markers viz; anthocyanin (34.02%), proline (45.00%), flavonoids (20.26%), lipid peroxidation (10.00%), guaiacol peroxidase (36.58%), ascorbate peroxidase (41.50%), polyphenol oxidase (25.34%) and phenylalanine ammonia-lyase (2.10 fold) as compared to untreated diseased plants. Increased biochemical content specifically sugar (15.43%), phenolics (49.10%), chlorophyll, and carotenoids were measured in Ch@BSNP-treated diseased plants compared to untreated X. campestris-infested plants. The Ch@BSNP considerably reduced stress by increasing net photosynthetic rate and water use efficiency along with decreased transpiration rate and stomatal conductance in comparison to infected plants. Additionally, the expression of defense-regulatory genes viz; growth responsive (AUX, GH3, SAUR), early defense responsive (WRKYTF22, WRKY33, NOS1), defense responsive (PR1, NHO1, NPR1), hypersensitivity responsive (Pti, RbohD, OXI1) and stress hormones responsive (MYC2, JAR1, ERF1) were found to be upregulated in diseased plants while being significantly downregulated in Ch@BSNP-treated diseased plants. Furthermore, fruits obtained from pathogen-compromised plants treated with Ch@BSNP had higher levels of health-promoting compounds including lycopene and beta-carotene than infected plant fruits. This nano-enabled and environmentally safer crop protection strategy may encourage a sustainable agri-system towards the world's growing food demand and promote food security.

Targeted and untargeted metabolomics reveals deep analysis of drought stress responses in needles and roots of Pinus taeda seedlings

Drought stress is one of major environmental stresses affecting plant growth and yield. Although Pinus taeda trees are planted in rainy southern China, local drought sometime occurs and can last several months, further affecting their growth and resin production. In this study, P. taeda seedlings were treated with long-term drought (42 d), and then targeted and untargeted metabolomics analysis were carried out to evaluate drought tolerance of P. taeda. Targeted metabolomics analysis showed that levels of some sugars, phytohormones, and amino acids significantly increased in the roots and needles of water-stressed (WS) P. taeda seedlings, compared with well-watered (WW) pine seedlings. These metabolites included sucrose in pine roots, the phytohormones abscisic acid and sacylic acid in pine needles, the phytohormone gibberellin (GA4) and the two amino acids, glycine and asparagine, in WS pine roots. Compared with WW pine seedlings, the neurotransmitter acetylcholine significantly increased in needles of WS pine seedlings, but significantly reduced in their roots. The neurotransmitters L-glutamine and hydroxytyramine significantly increased in roots and needles of WS pine seedlings, respectively, compared with WW pine seedlings, but the neurotransmitter noradrenaline significantly reduced in needles of WS pine seedlings. Levels of some unsaturated fatty acids significantly reduced in roots or needles of WS pine seedlings, compared with WW pine seedlings, such as linoleic acid, oleic acid, myristelaidic acid, myristoleic acid in WS pine roots, and palmitelaidic acid, erucic acid, and alpha-linolenic acid in WS pine needles. However, three saturated fatty acids significantly increased in WS pine seedlings, i.e., dodecanoic acid in WS pine needles, tricosanoic acid and heptadecanoic acid in WS pine roots. Untargeted metabolomics analysis showed that levels of some metabolites increased in WS pine seedlings, especially sugars, long-chain lipids, flavonoids, and terpenoids. A few of specific metabolites increased greatly, such as androsin, piceatanol, and panaxatriol in roots and needles of WS pine seedlings. Comparing with WW pine seedlings, it was found that the most enriched pathways in WS pine needles included flavone and flavonol biosynthesis, ABC transporters, diterpenoid biosynthesis, plant hormone signal transduction, and flavonoid biosynthesis; in WS pine roots, the most enriched pathways included tryptophan metabolism, caffeine metabolism, sesquiterpenoid and triterpenoid biosynthesis, plant hormone signal transduction, biosynthesis of phenylalanine, tyrosine, and tryptophan. Under long-term drought stress, P. taeda seedlings showed their own metabolomics characteristics, and some new metabolites and biosynthesis pathways were found, providing a guideline for breeding drought-tolerant cultivars of P. taeda.

The cassava (Manihot-esculenta Crantz)'s nitrate transporter NPF4.5, expressed in seedling roots, involved in nitrate flux and osmotic stress

AtNPF4.5/AIT2, which was predicted to be a low-affinity transporter capable for nitrate uptake, was screened by ABA receptor complex in Arabidopsis ten years ago. However, the molecular and biochemical characterizations of AtNPF4.5 in plants remained largely unclear. In this study, the function of a plasma-membrane-localized and root-specifically-expressed gene MeNPF4.5 (Manihot-esculenta NITRATE TRANSPORTER 1 PTR FAMILY4.5), an ortholog of the Arabidopsis thaliana NPF4.5, was investigated in cassava roots as a nitrate efflux transporter on low nitrate medium and an influx transporter following exposure to high concentration of external nitrates. Moreover, RNA interference (RNAi) of MeNPF4.5 reduced the nitrate efflux capacity but the overexpressing cassava seedlings increased the ability of efflux from the elongation to the mature zone of root under low nitrate treatments. Besides, MeNPF4.5-RNAi expression reduced the nitrate influx capacity but enhanced nitrate absorption in parts of overexpressing plants from the meristem, elongation to mature zone of roots under high nitrate conditions. Furthermore, MeNPF4.5-RNAi seedlings survived owing to roots that could grow normally, but the MeNPF4.5-over-expressors showed adverse growth under 7% PEG6000 stress, suggesting that MeNPF4.5 negatively regulated the osmotic stress and was involved in nitrate flux through cassava seedlings.

Bipartite phosphoinositide-dependent modulation of auxin signaling during xylem differentiation in Arabidopsis thaliana roots

Efficient root-to-shoot delivery of water and nutrients in plants relies on the correct differentiation of xylem cells into hollow elements. While auxin is integral to the formation of xylem cells, it remains poorly characterized how each subcellular pool of this hormone regulates this process. Combining genetic and cell biological approaches, we investigated the bipartite activity of nucleoplasmic vs plasma membrane-associated phosphatidylinositol 4-phosphate kinases PIP5K1 and its homolog PIP5K2 in Arabidopsis thaliana roots and uncovered a novel mechanism by which phosphoinositides integrate distinct aspects of the auxin signaling cascade and, in turn, regulate the onset of xylem differentiation. The appearance of undifferentiated cells in protoxylem strands of pip5k1 pip5k2 is phenomimicked in auxin transport and perception mutants and can be partially restored by the nuclear residence of PIP5K1. By contrast, exclusion of PIP5K1 from the nucleus hinders the auxin-mediated induction of the xylem master regulator VASCULAR RELATED NAC DOMAIN (VND) 7. A xylem-specific increase of auxin levels abolishes pip5k1 pip5k2 vascular defects, indicating that the establishment of auxin maxima is required to activate VND7-mediated xylem differentiation. Our results describe a new mechanism by which distinct subcellular pools of phosphoinositides integrate auxin transport and perception to initiate xylem differentiation in a spatiotemporal manner.

Genome-wide analysis of the JAZ subfamily of transcription factors and functional verification of BnC08.JAZ1-1 in Brassica napus

BACKGROUND

JAZ subfamily plays crucial roles in growth and development, stress, and hormone responses in various plant species. Despite its importance, the structural and functional analyses of the JAZ subfamily in Brassica napus are still limited.

RESULTS

Comparing to the existence of 12 JAZ genes (AtJAZ1-AtJAZ12) in Arabidopsis, there are 28, 31, and 56 JAZ orthologues in the reference genome of B. rapa, B. oleracea, and B. napus, respectively, in accordance with the proven triplication events during the evolution of Brassicaceae. The phylogenetic analysis showed that 127 JAZ proteins from A. thaliana, B. rapa, B. oleracea, and B. napus could fall into five groups. The structure analysis of all 127 JAZs showed that these proteins have the common motifs of TIFY and Jas, indicating their conservation in Brassicaceae species. In addition, the cis-element analysis showed that the main motif types are related to phytohormones, biotic and abiotic stresses. The qRT-PCR of the representative 11 JAZ genes in B. napus demonstrated that different groups of BnJAZ individuals have distinct patterns of expression under normal conditions or treatments with distinctive abiotic stresses and phytohormones. Especially, the expression of BnJAZ52 (BnC08.JAZ1-1) was significantly repressed by abscisic acid (ABA), gibberellin (GA), indoleacetic acid (IAA), polyethylene glycol (PEG), and NaCl treatments, while induced by methyl jasmonate (MeJA), cold and waterlogging. Expression pattern analysis showed that BnC08.JAZ1-1 was mainly expressed in the vascular bundle and young flower including petal, pistil, stamen, and developing ovule, but not in the stem, leaf, and mature silique and seed. Subcellular localization showed that the protein was localized in the nucleus, in line with its orthologues in Arabidopsis. Overexpression of BnC08.JAZ1-1 in Arabidopsis resulted in enhanced seed weight, likely through regulating the expression of the downstream response genes involved in the ubiquitin-proteasome pathway and phospholipid metabolism pathway.

CONCLUSIONS

The systematic identification, phylogenetic, syntenic, and expression analyses of BnJAZs subfamily improve our understanding of their roles in responses to stress and phytohormone in B. napus. In addition, the preliminary functional validation of BnC08.JAZ1-1 in Arabidopsis demonstrated that this subfamily might also play a role in regulating seed weight.

Transcriptome Analysis Reveals the Regulatory Networks of Cytokinin in Promoting Floral Feminization in Castanea henryi

Castanea henryi is a monoecious plant with a low female-to-male ratio, which limits its yield. The phytohormone cytokinin (CK) plays a crucial role in flower development, especially gynoecium development. Here, the feminizing effect of CK on the development of C. henryi was confirmed by the exogenous spraying of N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU). Spraying CPPU at 125 mg·L^-1 thrice changed the male catkin into a pure female catkin, whereas at 5 mg·L^-1 and 25 mg·L^-1, only a part of the male catkin was transformed into a female catkin. A comparative transcriptome analysis of male catkins subjected to CPPU was performed to study the mechanism of the role of CKs in sex differentiation. Using Pearson's correlation analysis between hormone content and hormone synthesis gene expression, four key genes, LOG1, LOG3, LOG7 and KO, were identified in the CK and GA synthesis pathways. Moreover, a hub gene in the crosstalk between JA and the other hormone signaling pathways, MYC2, was identified, and 15 flowering-related genes were significantly differentially expressed after CPPU treatment. These results suggest that CK interacts with other phytohormones to determine the sex of C. henryi, and CK may directly target floral organ recognition genes to control flower sex.

Cytokinin Confers Brown Planthopper Resistance by Elevating Jasmonic Acid Pathway in Rice

Plants have evolved a sophisticated defense system that employs various hormone pathways to defend against attacks by insect pests. Cytokinin (CK) plays an important role in plant growth and stress tolerance, but the role of CKs in plant-insect interaction remains largely unclear. Here, we report that CKs act as a positive regulator in rice resistance against brown planthopper (BPH), a devastating insect pest of rice. We found that BPH feeding promotes CK biosynthesis and signaling in rice. Exogenous application of CKs significantly increased the rice resistance to BPH. Increasing endogenous CKs by knocking out cytokinin oxidase/dehydrogenase (OsCKXs) led to enhanced resistance to BPH. Moreover, the levels of the plant hormone jasmonic acid (JA) and the expression of JA-responsive genes were elevated by CK treatment and in OsCKXs knockout plants. Furthermore, JA-deficient mutant og1 was more susceptible to BPH, and CK-induced BPH resistance was suppressed in og1. These results indicate that CK-mediated BPH resistance is JA-dependent. Our findings provide the direct evidence for the novel role of CK in promoting insect resistance, and demonstrate that CK-induced insect resistance is JA-dependent. These results provide important guidance for effective pest management strategies in the future.

Understanding the root xylem plasticity for designing resilient crops

Xylem is the main route for transporting water, minerals and a myriad of signalling molecules within the plant. With its onset during early embryogenesis, the development of the xylem relies on hormone gradients, the activity of unique transcription factors, the distribution of mobile microRNAs, and receptor-ligand pathways. These regulatory mechanisms are often interconnected and together contribute to the plasticity of this water-conducting tissue. Environmental stresses, such as drought and salinity, have a great impact on xylem patterning. A better understanding of how the structural properties of the xylem are regulated in normal and stress conditions will be instrumental in developing crops of the future. In addition, vascular wilt pathogens that attack the xylem are becoming increasingly problematic. Further knowledge of xylem development in response to these pathogens will bring new solutions against these diseases. In this review, we summarize recent findings on the molecular mechanisms of xylem formation that largely come from Arabidopsis research with additional insights from tomato and monocot species. We emphasize the impact of abiotic factors and pathogens on xylem plasticity and the urgent need to uncover the underlying mechanisms. Finally, we discuss the multidisciplinary approach to model xylem capacities in crops.

Evaluation of high salinity tolerance in Pongamia pinnata (L.) Pierre by a systematic analysis of hormone-metabolic network

Salinity stress results in significant losses in plant productivity and loss of cultivable lands. Although Pongamia pinnata is reported to be a salt-tolerant semiarid biofuel tree, the adaptive mechanisms to saline environments are elusive. Despite a reduction in carbon exchange rate (CER), the unchanged relative water content provides no visible salinity induced symptoms in leaves of hydroponic cultivated Pongamia seedlings for 8 days. Our Na⁺ -specific fluorescence results demonstrated that there was an effective apoplastic sodium sequestration in the roots. Salinity stress significantly increased zeatin (~5.5-fold), and jasmonic acid (~3.8-fold) levels in leaves while zeatin (~2.5-fold) content increased in leaves as well as in roots of salt-treated plants. Metabolite analysis suggested that osmolytes such as myo-inositol and mannitol were enhanced by ~12-fold in leaves and roots of salt-treated plants. Additionally, leaves of Pongamia showed a significant enhancement in carbohydrate content, while fatty acids were accumulated in roots under salt stress condition. At the molecular level, salt stress enhanced the expression of genes related to transporters, including the Salt Overly Sensitive 2 gene (SOS2), SOS3, vacuolar-cation/proton exchanger, and vacuolar-proton/ATPase exclusively in leaves, whereas the Sodium Proton Exchanger1 (NHX1), Cation Calcium Exchanger (CCX), and Cyclic Nucleotide Gated Channel 5 (CNGC5) were up-regulated in roots. Antioxidant gene expression analysis clearly demonstrated that peroxidase levels were significantly enhanced by ~10-fold in leaves, while Catalase and Fe-superoxide Dismutase (Fe-SOD) genes were increased in roots under salt stress. The correlation interaction studies between phytohormones and metabolites revealed new insights into the molecular and metabolic adaptations that confer salinity tolerance to Pongamia.

The Danger-Associated Peptide PEP1 Directs Cellular Reprogramming in the Arabidopsis Root Vascular System

When perceiving microbe-associated molecular patterns (MAMPs) or plant-derived damage-associated molecular patterns (DAMPs), plants alter their root growth and development by displaying a reduction in the root length and the formation of root hairs and lateral roots. The exogenous application of a MAMP peptide, flg22, was shown to affect root growth by suppressing meristem activity. In addition to MAMPs, the DAMP peptide PEP1 suppresses root growth while also promoting root hair formation. However, the question of whether and how these elicitor peptides affect the development of the vascular system in the root has not been explored. The cellular receptors of PEP1, PEPR1 and PEPR2 are highly expressed in the root vascular system, while the receptors of flg22 (FLS2) and elf18 (EFR) are not. Consistent with the expression patterns of PEP1 receptors, we found that exogenously applied PEP1 has a strong impact on the division of stele cells, leading to a reduction of these cells. We also observed the alteration in the number and organization of cells that differentiate into xylem vessels. These PEP1-mediated developmental changes appear to be linked to the blockage of symplastic connections triggered by PEP1. PEP1 dramatically disrupts the symplastic movement of free green fluorescence protein (GFP) from phloem sieve elements to neighboring cells in the root meristem, leading to the deposition of a high level of callose between cells. Taken together, our first survey of PEP1-mediated vascular tissue development provides new insights into the PEP1 function as a regulator of cellular reprogramming in the Arabidopsis root vascular system.

Protocatechuic acid attenuates lipopolysaccharide-induced septic lung injury in mice: The possible role through suppressing oxidative stress, inflammation and apoptosis

Here, we investigated the protective efficacy of protocatechuic acid (PCA) against lipopolysaccharide (LPS)-induced septic lung injury. Eighty-two male Balb/c mice were divided into six groups: control, PCA30 (30 mg/kg), LPS (10 mg/kg), PCA10-LPS, PCA20-LPS, and PCA30-LPS treated with 10, 20 and 30 mg/kg PCA, respectively, for seven days before intraperitoneal LPS injection. PCA pre-treatment, especially at higher dose, significantly reduced LPS-induced lung tissue injury as indicated by increased heat shock protein 70 and antioxidant molecules (reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) accompanied by lower oxidative stress indices (malondialdehyde and nitric oxide). PCA administration decreased inflammatory mediators including myeloperoxidase, nuclear factor kappa B (NF-κB p65), and pro-inflammatory cytokines, and prevented the development of apoptotic events in the lung tissue. At the molecular level, PCA downregulated mRNA expression of nitric oxide synthase 2, C/EBP homologous protein, and high mobility group box1 in the lungs of all PCA-LPS treated mice. Thus, PCA-pre-treatment effectively counteracted sepsis-induced acute lung injury in vivo by promoting and antioxidant status, while inhibiting inflammation and apoptosis. PRACTICAL IMPLICATIONS: Sepsis-mediated organ dysfunction and high mortality is aggravated by acute lung injury (ALI). Therefore, new therapeutic approaches are needed to encounter sepsis-mediated ALI. Protocatechuic acid (PCA) is a naturally occurring phenolic acid with various biological and pharmacological activities. PCA is abundant in edible plants including Allium cepa L., Oryza sativa L., Hibiscus sabdariffa, Prunus domestica L., and Eucommia ulmoides. In this investigation we studied the potential protective role of pure PCA (10, 20 and 30 mg/kg) on LPS-mediated septic lung injury in mice through examining oxidative challenge, inflammatory response, apoptotic events and histopathological changes in addition to evaluating the levels and mRNA expression of heat shock protein 70, C/EBP homologous protein and high mobility group box1 in the lung tissue. The recorded results showed that PCA pre-administration was able to significantly abrogate the damages in the lung tissue associated septic response. This protective effect comes from its strong antioxidant, anti-inflammatory, and anti-apoptotic activities, suggesting that PCA may be applied to alleviate ALI associated with the development of sepsis.

Alzheimer's disease alters oligodendrocytic glycolytic and ketolytic gene expression

INTRODUCTION

Sporadic Alzheimer's disease (AD) is strongly correlated with impaired brain glucose metabolism, which may affect AD onset and progression. Ketolysis has been suggested as an alternative pathway to fuel the brain.

METHODS

RNA-seq profiles of post mortem AD brains were used to determine whether dysfunctional AD brain metabolism can be determined by impairments in glycolytic and ketolytic gene expression. Data were obtained from the Knight Alzheimer's Disease Research Center (62 cases; 13 controls), Mount Sinai Brain Bank (110 cases; 44 controls), and the Mayo Clinic Brain Bank (80 cases; 76 controls), and were normalized to cell type: astrocytes, microglia, neurons, oligodendrocytes.

RESULTS

In oligodendrocytes, both glycolytic and ketolytic pathways were significantly impaired in AD brains. Ketolytic gene expression was not significantly altered in neurons, astrocytes, and microglia.

DISCUSSION

Oligodendrocytes may contribute to brain hypometabolism observed in AD. These results are suggestive of a potential link between hypometabolism and dysmyelination in disease physiology. Additionally, ketones may be therapeutic in AD due to their ability to fuel neurons despite impaired glycolytic metabolism.

Function and Mechanism of Jasmonic Acid in Plant Responses to Abiotic and Biotic Stresses

As sessile organisms, plants must tolerate various environmental stresses. Plant hormones play vital roles in plant responses to biotic and abiotic stresses. Among these hormones, jasmonic acid (JA) and its precursors and derivatives (jasmonates, JAs) play important roles in the mediation of plant responses and defenses to biotic and abiotic stresses and have received extensive research attention. Although some reviews of JAs are available, this review focuses on JAs in the regulation of plant stress responses, as well as JA synthesis, metabolism, and signaling pathways. We summarize recent progress in clarifying the functions and mechanisms of JAs in plant responses to abiotic stresses (drought, cold, salt, heat, and heavy metal toxicity) and biotic stresses (pathogen, insect, and herbivore). Meanwhile, the crosstalk of JA with various other plant hormones regulates the balance between plant growth and defense. Therefore, we review the crosstalk of JAs with other phytohormones, including auxin, gibberellic acid, salicylic acid, brassinosteroid, ethylene, and abscisic acid. Finally, we discuss current issues and future opportunities in research into JAs in plant stress responses.

Role of jasmonic acid in plants: the molecular point of view

Recent updates in JA biosynthesis, signaling pathways and the crosstalk between JA and others phytohormones in relation with plant responses to different stresses. In plants, the roles of phytohormone jasmonic acid (JA), amino acid conjugate (e.g., JA-Ile) and their derivative emerged in last decades as crucial signaling compounds implicated in stress defense and development in plants. JA has raised a great interest, and the number of researches on JA has increased rapidly highlighting the importance of this phytohormone in plant life. First, JA was considered as a stress hormone implicated in plant response to biotic stress (pathogens and herbivores) which confers resistance to biotrophic and hemibiotrophic pathogens contrarily to salicylic acid (SA) which is implicated in plant response to necrotrophic pathogens. JA is also implicated in plant responses to abiotic stress (such as soil salinity, wounding and UV). Moreover, some researchers have recently revealed that JA controls several physiological processes like root growth, growth of reproductive organs and, finally, plant senescence. JA is also involved in the biosynthesis of various metabolites (e.g., phytoalexins and terpenoids). In plants, JA signaling pathways are well studied in few plants essentially Arabidopsis thaliana, Nicotiana benthamiana, and Oryza sativa L. confirming the crucial role of this hormone in plants. In this review, we highlight the last foundlings about JA biosynthesis, JA signaling pathways and its implication in plant maturation and response to environmental constraints.

Crosstalk between phytohormones and secondary metabolites in the drought stress tolerance of crop plants: A review

Drought stress negatively affects crop performance and weakens global food security. It triggers the activation of downstream pathways, mainly through phytohormones homeostasis and their signaling networks, which further initiate the biosynthesis of secondary metabolites (SMs). Roots sense drought stress, the signal travels to the above-ground tissues to induce systemic phytohormones signaling. The systemic signals further trigger the biosynthesis of SMs and stomatal closure to prevent water loss. SMs primarily scavenge reactive oxygen species (ROS) to protect plants from lipid peroxidation and also perform additional defense-related functions. Moreover, drought-induced volatile SMs can alert the plant tissues to perform drought stress mitigating functions in plants. Other phytohormone-induced stress responses include cell wall and cuticle thickening, root and leaf morphology alteration, and anatomical changes of roots, stems, and leaves, which in turn minimize the oxidative stress, water loss, and other adverse effects of drought. Exogenous applications of phytohormones and genetic engineering of phytohormones signaling and biosynthesis pathways mitigate the drought stress effects. Direct modulation of the SMs biosynthetic pathway genes or indirect via phytohormones' regulation provides drought tolerance. Thus, phytohormones and SMs play key roles in plant development under the drought stress environment in crop plants.

Exogenous methyl jasmonate promotes salt stress-induced growth inhibition and prioritizes defense response of Nitraria tangutorum Bobr

Jasmonates (JAs) play a key role in the regulation of growth and the defense response to environmental stresses. JAs inhibit plant growth and promote defense response. However, their roles in desert halophyte in the response to salt stress remain poorly understood. The effects of the combination of methyl jasmonate (MeJA) and NaCl treatment (the "MeN" condition) on the growth regulation and defense response of Nitraria tangutorum seedlings were investigated. Compared with NaCl treatment alone, exogenous MeJA aggravated the growth inhibition of seedlings by antagonizing to growth-related hormones and suppressing the transcript levels of these hormones-responsive genes, including gibberellin (GA)-responsive NtPIF3, NtGAST1, NtGSAT4, and cytokinin (CYT)-responsive NtARR1, NtARR11, NtARR12. Meanwhile, exogenous MeJA enhanced defense response and alleviated the stress damage by increasing antioxidase activity and antioxidant content, accumulating more osmolytes, maintaining lower Na⁺ /K⁺ ratios in shoots and higher Na⁺ efflux rates in roots of plants. In addition, exogenous MeJA increased the contents of endogenous JA and ABA, and the transcript levels of genes involved in their biosynthesis and responsiveness, thereby further regulating the transcript levels of defense response genes. These findings suggest that exogenous MeJA increases salt stress-induced growth inhibition and prioritizes the defensive responses (e.g. antioxidant defense, osmotic adjustment, and ion homeostasis) of N. tangutorum. These effects may be related to the amplification of jasmonic acid (JA) and abscisic acid (ABA) signals.

Oral intake of Lactobacillus plantarum L-14 extract alleviates TLR2- and AMPK-mediated obesity-associated disorders in high-fat-diet-induced obese C57BL/6J mice

OBJECTIVES

Whether periodic oral intake of postbiotics positively affects weight regulation and prevents obesity-associated diseases in vivo is unclear. This study evaluated the action mechanism of Lactobacillus plantarum L-14 (KTCT13497BP) extract and the effects of its periodic oral intake in a high-fat-diet (HFD) mouse model.

MATERIALS AND METHODS

Mouse pre-adipocyte 3T3-L1 cells and human bone marrow mesenchymal stem cells (hBM-MSC) were treated with L-14 extract every 2 days during adipogenic differentiation, and the mechanism underlying anti-adipogenic effects was analysed at cellular and molecular levels. L-14 extract was orally administrated to HFD-feeding C57BL/6J mice every 2 days for 7 weeks. White adipose tissue was collected and weighed, and liver and blood serum were analysed. The anti-adipogenic mechanism of exopolysaccharide (EPS) isolated from L-14 extract was also analysed using Toll-like receptor 2 (TLR2) inhibitor C29.

RESULTS

L-14 extract inhibited 3T3-L1 and hBM-MSC differentiation into mature adipocytes by upregulating AMPK signalling pathway in the early stage of adipogenic differentiation. The weight of the HFD + L-14 group (31.51 ± 1.96 g) was significantly different from that of the HFD group (35.14 ± 3.18 g). L-14 extract also significantly decreased the serum triacylglycerol/high-density lipoprotein cholesterol ratio (an insulin resistance marker) and steatohepatitis. In addition, EPS activated the AMPK signalling pathway by interacting with TLR2, consequently inhibiting adipogenesis.

CONCLUSIONS

EPS from L-14 extract inhibits adipogenesis via TLR2 and AMPK signalling pathways, and oral intake of L-14 extract improves obesity and obesity-associated diseases in vivo. Therefore, EPS can be used to prevent and treat obesity and metabolic disorders.

Jasmonates and Plant Salt Stress: Molecular Players, Physiological Effects, and Improving Tolerance by Using Genome-Associated Tools

Soil salinity is one of the most limiting stresses for crop productivity and quality worldwide. In this sense, jasmonates (JAs) have emerged as phytohormones that play essential roles in mediating plant response to abiotic stresses, including salt stress. Here, we reviewed the mechanisms underlying the activation and response of the JA-biosynthesis and JA-signaling pathways under saline conditions in Arabidopsis and several crops. In this sense, molecular components of JA-signaling such as MYC2 transcription factor and JASMONATE ZIM-DOMAIN (JAZ) repressors are key players for the JA-associated response. Moreover, we review the antagonist and synergistic effects between JA and other hormones such as abscisic acid (ABA). From an applied point of view, several reports have shown that exogenous JA applications increase the antioxidant response in plants to alleviate salt stress. Finally, we discuss the latest advances in genomic techniques for the improvement of crop tolerance to salt stress with a focus on jasmonates.

Plant vascular development: mechanisms and environmental regulation

Plant vascular development is a complex process culminating in the generation of xylem and phloem, the plant transporting conduits. Xylem and phloem arise from specialized stem cells collectively termed (pro)cambium. Once developed, xylem transports mainly water and mineral nutrients and phloem transports photoassimilates and signaling molecules. In the past few years, major advances have been made to characterize the molecular, genetic and physiological aspects that govern vascular development. However, less is known about how the environment re-shapes the process, which molecular mechanisms link environmental inputs with developmental outputs, which gene regulatory networks facilitate the genetic adaptation of vascular development to environmental niches, or how the first vascular cells appeared as an evolutionary innovation. In this review, we (1) summarize the current knowledge of the mechanisms involved in vascular development, focusing on the model species Arabidopsis thaliana, (2) describe the anatomical effect of specific environmental factors on the process, (3) speculate about the main entry points through which the molecular mechanisms controlling of the process might be altered by specific environmental factors, and (4) discuss future research which could identify the genetic factors underlying phenotypic plasticity of vascular development.

What drives interspecies graft union success? Exploring the role of phylogenetic relatedness and stem anatomy

The underlying mechanisms that determine whether two species can form a successful graft union (graft compatibility) remain obscure. Two prominent hypotheses are (1) the more closely related species are, the higher the graft success and (2) the vascular anatomy at the graft junction influences graft success. In this paper these two hypotheses are examined in a systematic way using graft combinations selected from a range of (a) phylogenetically close and more distant legume species, (b) species displaying different germination patterns and (c) scions and rootstocks possessing contrasting stem tissues and vascular patterns. Relatedness of species was not a good predictor of graft compatibility, as vascular reconnection can occur between distantly related species and can fail to occur in some more closely related species. Similarly, neither the stem tissues present at the graft junction nor the vascular anatomy correlated with the success of vascular reconnection. Relatedness and stem anatomy therefore do not appear to be the determining factors in successful vascular reconnection after grafting in legumes. These results are discussed in conjunction with other hypotheses such as the role of auxin.

Coping With Water Limitation: Hormones That Modify Plant Root Xylem Development

Periods of drought, that threaten crop production, are expected to become more prominent in large parts of the world, making it necessary to explore all aspects of plant growth and development, to breed, modify and select crops adapted to such conditions. One such aspect is the xylem, where influencing the size and number of the water-transporting xylem vessels, may impact on hydraulic conductance and drought tolerance. Here, we focus on how plants adjust their root xylem as a response to reduced water availability. While xylem response has been observed in a wide array of species, most of our knowledge on the molecular mechanisms underlying xylem plasticity comes from studies on the model plant Arabidopsis thaliana. When grown under water limiting conditions, Arabidopsis rapidly adjusts its development to produce more xylem strands with altered identity in an abscisic acid (ABA) dependent manner. Other hormones such as auxin and cytokinin are essential for vascular patterning and differentiation. Their balance can be perturbed by stress, as evidenced by the effects of enhanced jasmonic acid signaling, which results in similar xylem developmental alterations as enhanced ABA signaling. Furthermore, brassinosteroids and other signaling molecules involved in drought tolerance can also impact xylem development. Hence, a multitude of signals affect root xylem properties and, potentially, influence survival under water limiting conditions. Here, we review the likely entangled signals that govern root vascular development, and discuss the importance of taking root anatomical traits into account when breeding crops for enhanced resilience toward changes in water availability.

Bacterial Compound N,N-Dimethylhexadecylamine Modulates Expression of Iron Deficiency and Defense Response Genes in Medicago truncatula Independently of the Jasmonic Acid Pathway

Plants face a variety of biotic and abiotic stresses including attack by microbial phytopathogens and nutrient deficiencies. Some bacterial volatile organic compounds (VOCs) activate defense and iron-deficiency responses in plants. To establish a relationship between defense and iron deficiency through VOCs, we identified key genes in the defense and iron-deprivation responses of the legume model Medicago truncatula and evaluated the effect of the rhizobacterial VOC N,N-dimethylhexadecylamine (DMHDA) on the gene expression in these pathways by RT-qPCR. DMHDA increased M. truncatula growth 1.5-fold under both iron-sufficient and iron-deficient conditions compared with untreated plants, whereas salicylic acid and jasmonic acid decreased growth. Iron-deficiency induced iron uptake and defense gene expression. Moreover, the effect was greater in combination with DMHDA. Salicylic acid, Pseudomonas syringae, jasmonic acid, and Botrytis cinerea had inhibitory effects on growth and iron response gene expression but activated defense genes. Taken together, our results showed that the VOC DMHDA activates defense and iron-deprivation pathways while inducing a growth promoting effect unlike conventional phytohormones, highlighting that DMHDA does not mimic jasmonic acid but induces an alternative pathway. This is a novel aspect in the complex interactions between biotic and abiotic stresses.

Role of the Cytokinin-Activated Type-B Response Regulators in Hormone Crosstalk

Cytokinin is an important phytohormone that employs a multistep phosphorelay to transduce the signal from receptors to the nucleus, culminating in activation of type-B response regulators which function as transcription factors. Recent chromatin immunoprecipitation-sequencing (ChIP-seq) studies have identified targets of type-B ARABIDOPSIS RESPONSE REGULATORs (ARRs) and integrated these into the cytokinin-activated transcriptional network. Primary targets of the type-B ARRs are enriched for genes involved in hormonal regulation, emphasizing the extensive crosstalk that can occur between cytokinin, auxin, abscisic acid, brassinosteroids, gibberellic acid, ethylene, jasmonic acid, and salicylic acid. Examination of hormone-related targets reveals multiple regulatory points including biosynthesis, degradation/inactivation, transport, and signal transduction. Here, we consider this early response to cytokinin in terms of the hormones involved, points of regulatory crosstalk, and physiological significance.

Crosstalk with Jasmonic Acid Integrates Multiple Responses in Plant Development

To date, extensive studies have identified many classes of hormones in plants and revealed the specific, nonredundant signaling pathways for each hormone. However, plant hormone functions largely overlap in many aspects of plant development and environmental responses, suggesting that studying the crosstalk among plant hormones is key to understanding hormonal responses in plants. The phytohormone jasmonic acid (JA) is deeply involved in the regulation of plant responses to biotic and abiotic stresses. In addition, a growing number of studies suggest that JA plays an essential role in the modulation of plant growth and development under stress conditions, and crosstalk between JA and other phytohormones involved in growth and development, such as gibberellic acid (GA), cytokinin, and auxin modulate various developmental processes. This review summarizes recent findings of JA crosstalk in the modulation of plant growth and development, focusing on JA–GA, JA–cytokinin, and JA–auxin crosstalk. The molecular mechanisms underlying this crosstalk are also discussed.

MYC2 regulates ARR16, a component of cytokinin signaling pathways, in Arabidopsis seedling development

MYC2 is a basic helix-loop-helix transcription factor that acts as a repressor of blue light-mediated photomorphogenic growth; however, it promotes lateral root formation. MYC2 also regulates different phytohormone-signaling pathways in crucial manner. Arabidopsis response regulator 16 (ARR16) is a negative regulator of cytokinin signaling pathways. Here, we show that MYC2 directly binds to the E-box of ARR16 minimal promoter and negatively regulates its expression in a cytokinin-dependent manner. While ARR16 and MYC2 influence jasmonic acid and cytokinin signaling, the expression of ARR16 is regulated by cry1, GBF1, and HYH, the components of light signaling pathways. The transgenic studies show that the expression of ARR16 is regulated by MYC2 at various stages of development. The mutational studies reveal that ARR16 positively regulates the hypocotyl growth in blue light, and phenotypic analysis of atmyc2 arr16 double mutant further reveals that arr16 can suppress the short hypocotyl phenotype of atmyc2. Altogether, this work highlights MYC2-mediated transcriptional repression of ARR16 in Arabidopsis seedling development.

Identifying Temporally Regulated Root Nodulation Biomarkers Using Time Series Gene Co-Expression Network Analysis

Root nodulation results from a symbiotic relationship between a plant host and Rhizobium bacteria. Synchronized gene expression patterns over the course of rhizobial infection result in activation of pathways that are unique but overlapping with the highly conserved pathways that enable mycorrhizal symbiosis. We performed RNA sequencing of 30 Medicago truncatula root maturation zone samples at five distinct time points. These samples included plants inoculated with Sinorhizobium medicae and control plants that did not receive any Rhizobium. Following gene expression quantification, we identified 1,758 differentially expressed genes at various time points. We constructed a gene co-expression network (GCN) from the same data and identified link community modules (LCMs) that were comprised entirely of differentially expressed genes at specific time points post-inoculation. One LCM included genes that were up-regulated at 24 h following inoculation, suggesting an activation of allergen family genes and carbohydrate-binding gene products in response to Rhizobium. We also identified two LCMs that were comprised entirely of genes that were down regulated at 24 and 48 h post-inoculation. The identity of the genes in these modules suggest that down-regulating specific genes at 24 h may result in decreased jasmonic acid production with an increase in cytokinin production. At 48 h, coordinated down-regulation of a specific set of genes involved in lipid biosynthesis may play a role in nodulation. We show that GCN-LCM analysis is an effective method to preliminarily identify polygenic candidate biomarkers of root nodulation and develop hypotheses for future discovery.

Jasmonic Acid Methyl Ester Induces Xylogenesis and Modulates Auxin-Induced Xylary Cell Identity with NO Involvement

In Arabidopsis basal hypocotyls of dark-grown seedlings, xylary cells may form from the pericycle as an alternative to adventitious roots. Several hormones may induce xylogenesis, as Jasmonic acid (JA), as well as indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) auxins, which also affect xylary identity. Studies with the ethylene (ET)-perception mutant ein3eil1 and the ET-precursor 1-aminocyclopropane-1-carboxylic acid (ACC), also demonstrate ET involvement in IBA-induced ectopic metaxylem. Moreover, nitric oxide (NO), produced after IBA/IAA-treatments, may affect JA signalling and interact positively/negatively with ET. To date, NO-involvement in ET/JA-mediated xylogenesis has never been investigated. To study this, and unravel JA-effects on xylary identity, xylogenesis was investigated in hypocotyls of seedlings treated with JA methyl-ester (JAMe) with/without ACC, IBA, IAA. Wild-type (wt) and ein3eil1 responses to hormonal treatments were compared, and the NO signal was quantified and its role evaluated by using NO-donors/scavengers. Ectopic-protoxylem increased in the wt only after treatment with JAMe(10 μM), whereas in ein3eil1 with any JAMe concentration. NO was detected in cells leading to either xylogenesis or adventitious rooting, and increased after treatment with JAMe(10 μM) combined or not with IBA(10 μM). Xylary identity changed when JAMe was applied with each auxin. Altogether, the results show that xylogenesis is induced by JA and NO positively regulates this process. In addition, NO also negatively interacts with ET-signalling and modulates auxin-induced xylary identity.

Jasmonic Acid Modulates Xylem Development by Controlling Expression of PIN-FORMED 7

Jasmonic acid (JA) modulates plant development, growth, and responses to stress. Previously, we showed that in Arabidopsis thaliana, JA promotes the formation of extra xylem in roots, and mutant plants unable to express PIN-FORMED 3 (PIN3) and PIN7 formed extra xylem in the absence of exogenous JA. Those results suggested that JA modulates root xylem development by controlling PIN-mediated polar auxin transport. Consistent with this, treatment with an auxin transport inhibitor induced extra xylem formation. Here, we characterized the expression of PIN3 and PIN7 in JA-treated Arabidopsis plants. PIN3 expression was not altered in response to JA; by contrast, PIN7 expression was reduced by JA, which suggested that PIN7 is involved in JA-mediated xylem development. Indeed, overexpressing PIN7 suppressed the formation of extra xylem in response to JA. Based on these results, we propose that JA mediates xylem development by controlling polar auxin transport with PIN7 critically involved in this process.

Loss of Wood Formation Genes in Monocot Genomes

Woodiness (secondary xylem derived from vascular cambium) has been gained and lost multiple times in the angiosperms, but has been lost ancestrally in all monocots. Here, we investigate the conservation of genes involved in xylogenesis in fully sequenced angiosperm genomes, hypothesizing that monocots have lost some essential orthologs involved in this process. We analyzed the conservation of genes preferentially expressed in the developing secondary xylem of two eudicot trees in the sequenced genomes of 26 eudicot and seven monocot species, and the early diverging angiosperm Amborella trichopoda. We also reconstructed a regulatory model of early vascular cambial cell identity and differentiation and investigated the conservation of orthologs across the angiosperms. Additionally, we analyzed the genome of the aquatic seagrass Zostera marina for additional losses of genes otherwise essential to, especially, secondary cell wall formation. Despite almost complete conservation of orthology within the early cambial differentiation gene network, we show a clear pattern of loss of genes preferentially expressed in secondary xylem in the monocots that are highly conserved across eudicot species. Our study provides candidate genes that may have led to the loss of vascular cambium in the monocots, and, by comparing terrestrial angiosperms to an aquatic monocot, highlights genes essential to vasculature on land.

Plant hormone effects on isoprene emission from tropical tree in Ficus septica

Plant hormones and the circadian rhythm have been implicated in coordinated control of isoprene emission in plants. To gain insights into the signalling networks, foliar application of plant hormones was conducted in a native emitter, Ficus septica. Spraying of 50 μM jasmonic acid (JA) gradually decreased isoprene emission by 88% compared with initial levels within 5 days, and emission increased after relief from JA application. We further explored the molecular regulatory mechanism of isoprene emission by analysing photosynthetic rate, gene expression of 2-C-methyl-D-erythrytol 4-phosphate (MEP) pathway, hormone signalling and circadian rhythm processes, and metabolite pool sizes of MEP pathway. Results show that isoprene emission strongly correlated with isoprene synthase (IspS) gene expression and IspS protein levels over the period of JA treatment, indicating transcriptional and possible translational modulation of IspS by JA. Application of JA coordinately modulated genes in the auxin, cytokinin (CK), and circadian rhythm signal transduction pathways. Among the transcriptional factors analysed, MYC2 (JA) and LHY (circadian clock) negatively correlated with isoprene emission. Putative cis-elements predicted on IspS promoter (G-box for MYC2 and circadian for LHY) supports our proposal that isoprene emission is regulated by coordinated transcriptional modulation of IspS gene by phytohormone and circadian rhythm signalling.

What Makes the Wood? Exploring the Molecular Mechanisms of Xylem Acclimation in Hardwoods to an Ever-Changing Environment

Wood, also designated as secondary xylem, is the major structure that gives trees and other woody plants stability for upright growth and maintains the water supply from the roots to all other plant tissues. Over recent decades, our understanding of the cellular processes of wood formation (xylogenesis) has substantially increased. Plants as sessile organisms face a multitude of abiotic stresses, e.g., heat, drought, salinity and limiting nutrient availability that require them to adjust their wood structure to maintain stability and water conductivity. Because of global climate change, more drastic and sudden changes in temperature and longer periods without precipitation are expected to impact tree productivity in the near future. Thus, it is essential to understand the process of wood formation in trees under stress. Many traits, such as vessel frequency and size, fiber thickness and density change in response to different environmental stimuli. Here, we provide an overview of our current understanding of how abiotic stress factors affect wood formation on the molecular level focussing on the genes that have been identified in these processes.

Jasmonate Zim-Domain Protein 9 Interacts With Slender Rice 1 to Mediate the Antagonistic Interaction Between Jasmonic and Gibberellic Acid Signals in Rice

The jasmonic acid (JA) and gibberellic acid (GA) signaling pathways interact to coordinate stress responses and developmental processes. This coordination affects plant growth and yield, and is mediated by interactions between the repressors of each pathway, the JASMONATE ZIM-DOMAIN PROTEIN (JAZ) and DELLA proteins. In this study we attempted to identify rice (Oryza sativa) JAZs that interact with rice DELLAs such as SLENDER RICE 1 (SLR1). Analysis of protein-protein interactions showed that OsJAZ8 and OsJAZ9 interact with SLR1; OsJAZ9 also interacted with the SLR1-LIKE (SLRL) protein SLRL2. Based on this broader interaction, we explored the function of OsJAZ9 in JA and GA responses by analyzing transcript levels of the JA-responsive gene OsbHLH148 and the GA-responsive gene OsPIL14 in OsJAZ9-overexpressing (OsJAZ9-Ox) and osjaz9 mutant plants. OsbHLH148 and OsPIL14 encode key transcription factors controlling JA and GA responses, respectively, and JA and GA antagonistically regulate their expression. In OsJAZ9-Ox, the expression of OsbHLH148 was downregulated and the expression of OsPIL14 was upregulated. By contrast, in osjaz9 mutants, the expression of OsbHLH148 was upregulated and the expression of OsPIL14 was downregulated. These observations indicated that OsJAZ9 regulates both JA and GA responses in rice, and this finding was supported by the opposite expression patterns of OsDREB1s, downstream targets of OsbHLH148 and OsPIL14, in the OsJAZ9-Ox and osjaz9 plants. Together, these findings indicate that OsJAZ9 suppresses JA responses and promotes GA responses in rice, and the protein-protein interaction between OsJAZ9 and SLR1 is involved in the antagonistic interplay between JA and GA.

Plant Vascular Tissues-Connecting Tissue Comes in All Shapes

For centuries, humans have grown and used structures based on vascular tissues in plants. One could imagine that life would have developed differently without wood as a resource for building material, paper, heating energy, or fuel and without edible tubers as a food source. In this review, we will summarise the status of research on Arabidopsis thaliana vascular development and subsequently focus on how this knowledge has been applied and expanded in research on the wood of trees and storage organs of crop plants. We will conclude with an outlook on interesting open questions and exciting new research opportunities in this growing and important field.

Stress-Triggered Long-Distance Communication Leads to Phenotypic Plasticity: The Case of the Early Root Protoxylem Maturation Induced by Leaf Wounding in Arabidopsis

Root architecture and xylem phenotypic plasticity influence crop productivity by affecting water and nutrient uptake, especially under those environmental stress, which limit water supply or imply excessive water losses. Xylem maturation depends on coordinated events of cell wall lignification and developmental programmed cell death (PCD), which could both be triggered by developmental- and/or stress-driven hydrogen peroxide (H₂O₂) production. Here, the effect of wounding of the cotyledonary leaf on root protoxylem maturation was explored in Arabidopsis thaliana by analysis under Laser Scanning Confocal Microscope (LSCM). Leaf wounding induced early root protoxylem maturation within 3 days from the injury, as after this time protoxylem position was found closer to the tip. The effect of leaf wounding on protoxylem maturation was independent from root growth or meristem size, that did not change after wounding. A strong H₂O₂ accumulation was detected in root protoxylem 6 h after leaf wounding. Furthermore, the H₂O₂ trap N,N¹-dimethylthiourea (DMTU) reversed wound-induced early protoxylem maturation, confirming the need for H₂O₂ production in this signaling pathway.

miR172 Regulates both Vegetative and Reproductive Development in the Perennial Woody Plant Jatropha curcas

Jatropha curcas is a promising feedstock for biofuel production because its oil is highly suitable for processing bio-jet fuels and biodiesel. However, Jatropha exhibits a long juvenile stage in subtropical areas. miR172, a conserved small non-protein-coding RNA molecule with 21 nucleotides, regulates a wide range of developmental processes. To date, however, no studies have examined the function of miR172 in Jatropha. There are five miR172 precursors encoding two mature miR172s in Jatropha, which are expressed in all tissues, with the highest expression level in leaves, and the levels are up-regulated with age. Overexpression of JcmiR172a resulted in early flowering, abnormal flowers, and altered leaf morphology in transgenic Arabidopsis and Jatropha. The expression levels of miR172 target genes were down-regulated, and the flower identity genes were up-regulated in the JcmiR172a-overexpressing transgenic plants. Interestingly, we showed that JcmiR172 might be involved in regulation of stem vascular development through manipulating the expression of cellulose and lignin biosynthesis genes. Overexpression of JcmiR172a enhanced xylem development and reduced phloem and pith development. This study helped elucidate the functions of miR172 in perennial plants, a known age-related miRNA involved in the regulation of perennial plant phase change and organ development.

Jasmonate promotes auxin-induced adventitious rooting in dark-grown Arabidopsis thaliana seedlings and stem thin cell layers by a cross-talk with ethylene signalling and a modulation of xylogenesis

BACKGROUND

Adventitious roots (ARs) are often necessary for plant survival, and essential for successful micropropagation. In Arabidopsis thaliana dark-grown seedlings AR-formation occurs from the hypocotyl and is enhanced by application of indole-3-butyric acid (IBA) combined with kinetin (Kin). The same IBA + Kin-treatment induces AR-formation in thin cell layers (TCLs). Auxin is the main inducer of AR-formation and xylogenesis in numerous species and experimental systems. Xylogenesis is competitive to AR-formation in Arabidopsis hypocotyls and TCLs. Jasmonates (JAs) negatively affect AR-formation in de-etiolated Arabidopsis seedlings, but positively affect both AR-formation and xylogenesis in tobacco dark-grown IBA + Kin TCLs. In Arabidopsis the interplay between JAs and auxin in AR-formation vs xylogenesis needs investigation. In de-etiolated Arabidopsis seedlings, the Auxin Response Factors ARF6 and ARF8 positively regulate AR-formation and ARF17 negatively affects the process, but their role in xylogenesis is unknown. The cross-talk between auxin and ethylene (ET) is also important for AR-formation and xylogenesis, occurring through EIN3/EIL1 signalling pathway. EIN3/EIL1 is the direct link for JA and ET-signalling. The research investigated JA role on AR-formation and xylogenesis in Arabidopsis dark-grown seedlings and TCLs, and the relationship with ET and auxin. The JA-donor methyl-jasmonate (MeJA), and/or the ET precursor 1-aminocyclopropane-1-carboxylic acid were applied, and the response of mutants in JA-synthesis and -signalling, and ET-signalling investigated. Endogenous levels of auxin, JA and JA-related compounds, and ARF6, ARF8 and ARF17 expression were monitored.

RESULTS

MeJA, at 0.01 μM, enhances AR-formation, when combined with IBA + Kin, and the response of the early-JA-biosynthesis mutant dde2-2 and the JA-signalling mutant coi1-16 confirmed this result. JA levels early change during TCL-culture, and JA/JA-Ile is immunolocalized in AR-tips and xylogenic cells. The high AR-response of the late JA-biosynthesis mutant opr3 suggests a positive action also of 12-oxophytodienoic acid on AR-formation. The crosstalk between JA and ET-signalling by EIN3/EIL1 is critical for AR-formation, and involves a competitive modulation of xylogenesis. Xylogenesis is enhanced by a MeJA concentration repressing AR-formation, and is positively related to ARF17 expression.

CONCLUSIONS

The JA concentration-dependent role on AR-formation and xylogenesis, and the interaction with ET opens the way to applications in the micropropagation of recalcitrant species.

Cytokinin at the Crossroads of Abiotic Stress Signalling Pathways

Cytokinin is a multifaceted plant hormone that plays major roles not only in diverse plant growth and development processes, but also stress responses. We summarize knowledge of the roles of its metabolism, transport, and signalling in responses to changes in levels of both macronutrients (nitrogen, phosphorus, potassium, sulphur) and micronutrients (boron, iron, silicon, selenium). We comment on cytokinin's effects on plants' xenobiotic resistance, and its interactions with light, temperature, drought, and salinity signals. Further, we have compiled a list of abiotic stress-related genes and demonstrate that their expression patterns overlap with those of cytokinin metabolism and signalling genes.