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Authors: Yeling Zhou, Yuzhu Wang, Dong Zhang and Jiansheng Liang.
Molecular Plant (2024)
Abstract: "ATP-binding cassette (ABC) transporters are integral membrane proteins that have been evolved with diverse functions via transport of various substrates. In Arabidopsis, the G subfamily of ABC proteins is particularly abundant and participate in multiple signaling pathways during plant development and stress responses. Here, we revealed two Arabidopsis ABCG transporters, ABCG16 and ABCG25, were engaged in ABA-mediated stress responses and early plant growth through an endomembrane-specific dimerization-coupled transport of ABA and ABA-glucosyl ester (ABA-GE), respectively. We first disclosed that ABCG16 contributed to osmotic stress tolerance via ABA signaling. More specifically, ABCG16 acted in stimulation of cellular ABA efflux in both yeast and plant cells. Combined with FRET (Förster resonance energy transfer) analysis, we showed that ABCG16 formed obligatory homodimers for ABA export activity and that the plasma membrane resided ABCG16 homodimers specifically responded to ABA with notable conformational changes within the homodimers. Furthermore, we demonstrated that ABCG16 heterodimerized with ABCG25 at the ER membrane and facilitated the ER entry of ABA-GE in both Arabidopsis and tobacco cells. The specific responsiveness of the heterodimer ABCG16/ABCG25 to ABA-GE and the superior growth of the double mutant jat1-2abcg25 supported an inhibitory role of the two ABCGs in early seedling establishment via regulation of ABA-GE translocation across the ER membrane. Together, our endomembrane-specific analysis of the FRET signals derived from the homo- or heterodimerized ABCG complexes allowed us to link an endomembrane-biased dimerization partnership to distinct substrate translocation by ABCG transporters, providing a prototypic framework for understanding the omnipotence of ABCG transporters in plant development and stress responses."
Authors: Tianren Zhang, Li Bai and Yan Guo.
Science China Life Sciences (2024)
Abstract: "Hyperosmotic stress caused by drought is a detrimental threat to plant growth and agricultural productivity due to limited water availability. Stomata are gateways of transpiration and gas exchange, the swift adjustment of stomatal aperture has a strong influence on plant drought resistance. Despite intensive investigations of stomatal closure during drought stress in past decades, little is known about how sequential signals are integrated during complete processes. Here, we discovered that the rapid Ca2+ signaling and subsequent abscisic acid (ABA) signaling contribute to the kinetics of both F-actin reorganizations and stomatal closure in Arabidopsis thaliana, while STOMATAL CLOSURE-RELATED ACTIN BINDING PROTEIN1 (SCAB1) is the molecular switch for this entire process. During the early stage of osmotic shock responses, swift elevated calcium signaling promotes SCAB1 phosphorylation through calcium sensors CALCIUM DEPENDENT PROTEIN KINASE3 (CPK3) and CPK6. The phosphorylation restrained the microfilament binding affinity of SCAB1, which bring about the F-actin disassembly and stomatal closure initiation. As the osmotic stress signal continued, both the kinase activity of CPK3 and the phosphorylation level of SCAB1 attenuated significantly. We further found that ABA signaling is indispensable for these attenuations, which presumably contributed to the actin filament reassembly process as well as completion of stomatal closure. Notably, the dynamic changes of SCAB1 phosphorylation status are crucial for the kinetics of stomatal closure. Taken together, our results support a model in which SCAB1 works as a molecular switch, and directs the microfilament rearrangement through integrating the sequentially generated Ca2+ and ABA signals during osmotic stress induced stomatal closure."
Authors: Xi Chen, Chenchen Zhao, Ping Yun, Min Yu, Meixue Zhou, Zhong-Hua Chen and Sergey Shabala.
The Plant Journal (2024)
Abstract: "Developing climate-resilient crops is critical for future food security and sustainable agriculture under current climate scenarios. Of specific importance are drought and soil salinity. Tolerance traits to these stresses are highly complex, and the progress in improving crop tolerance is too slow to cope with the growing demand in food production unless a major paradigm shift in crop breeding occurs. In this work, we combined bioinformatics and physiological approaches to compare some of the key traits that may differentiate between xerophytes (naturally drought-tolerant plants) and mesophytes (to which the majority of the crops belong). We show that both xerophytes and salt-tolerant mesophytes have a much larger number of copies in key gene families conferring some of the key traits related to plant osmotic adjustment, abscisic acid (ABA) sensing and signalling, and stomata development. We show that drought and salt-tolerant species have (i) higher reliance on Na for osmotic adjustment via more diversified and efficient operation of Na+/H+ tonoplast exchangers (NHXs) and vacuolar H+- pyrophosphatase (VPPases); (ii) fewer and faster stomata; (iii) intrinsically lower ABA content; (iv) altered structure of pyrabactin resistance/pyrabactin resistance-like (PYR/PYL) ABA receptors; and (v) higher number of gene copies for protein phosphatase 2C (PP2C) and sucrose non-fermenting 1 (SNF1)-related protein kinase 2/open stomata 1 (SnRK2/OST1) ABA signalling components. We also show that the past trends in crop breeding for Na+ exclusion to improve salinity stress tolerance are counterproductive and compromise their drought tolerance. Incorporating these genetic insights into breeding practices could pave the way for more drought-tolerant and salt-resistant crops, securing agricultural yields in an era of climate unpredictability."
Authors: Gyanendra Kumar Rai, Sonal Mishra, Rekha Chouhan, Muntazir Mushtaq, Aksar Ali Chowdhary, Pradeep K. Rai, Ranjeet Ranjan Kumar, Pradeep Kumar, Francisco Perez-Alfocea, Giuseppe Colla, Mariateresa Cardarelli, Vikas Srivastava and Sumit G. Gandhi.
Frontiers in Plant Science (2023)
Abstract: "Salinity or salt stress has deleterious effects on plant growth and development. It imposes osmotic, ionic, and secondary stresses, including oxidative stress on the plants and is responsible for the reduction of overall crop productivity and therefore challenges global food security. Plants respond to salinity, by triggering homoeostatic mechanisms that counter salt-triggered disturbances in the physiology and biochemistry of plants. This involves the activation of many signaling components such as SOS pathway, ABA pathway, and ROS and osmotic stress signaling. These biochemical responses are accompanied by transcriptional modulation of stress-responsive genes, which is mostly mediated by salt-induced transcription factor (TF) activity. Among the TFs, the multifaceted significance of WRKY proteins has been realized in many diverse avenues of plants’ life including regulation of plant stress response. Therefore, in this review, we aimed to highlight the significance of salinity in a global perspective, the mechanism of salt sensing in plants, and the contribution of WRKYs in the modulation of plants’ response to salinity stress. This review will be a substantial tool to investigate this problem in different perspectives, targeting WRKY and offering directions to better manage salinity stress in the field to ensure food security."
Authors: Giulia Russo, Serena Capitanio, Marta Trasoletti, Cristina Morabito, Paolo Korwin Krukowski, Ivan Visentin, Andrea Genre, Andrea Schubert and Francesca Cardinale.
Journal of Experimental Botany (2023)
Abstract: The phytohormones strigolactones crosstalk with abscisic acid (ABA) in acclimation to osmotic stress, as ascertained in leaves. However, our knowledge about underground tissues is limited, and null in Arabidopsis. Namely, if strigolactones affect ABA transport across plasma membranes has never been addressed. We evaluated the effect of strigolactones on the localisation of ATP BINDING CASSETTE G25 (ABCG25), an ABA exporter in Arabidopsis thaliana. Wild-type, strigolactone-insensitive and -depleted seedlings expressing a GFP:ABCG25 construct were treated with ABA or strigolactones, and GFP was quantified by confocal microscopy in different subcellular compartments of epidermal root cells. We show that strigolactones promote the localisation of an ABA transporter at the plasma membrane by enhancing its endosomal recycling. Genotypes altered in strigolactone synthesis or perception are not impaired in ABCG25 recycling promotion by ABA, which acts downstream or independent of strigolactones in this respect. Additionally, we confirm that osmotic stress decreases strigolactone synthesis in A. thaliana root cells; and that such decrease may support local ABA retention under low water availability, by allowing ABCG25 internalisation. Thus, a new mechanism for ABA homeostasis regulation is proposed in the context of osmotic stress acclimation: the fine tuning by strigolactones of ABCG25 localisation in root cells."
Authors: Junhong Guo, Gerrit T. S. Beemster, Fulai Liu, Zongming Wang and Xiangnan Li.
International Journal of Molecular Sciences (2023
Abstract: "Abscisic acid (ABA) plays a vital role in the induction of low temperature tolerance in plants. To understand the molecular basis of this phenomenon, we performed a proteomic analysis on an ABA-deficit mutant barley (Az34) and its wild type (cv Steptoe) under control conditions (25/18 °C) and after exposure to 0 °C for 24 h. Most of the differentially abundant proteins were involved in the processes of photosynthesis and metabolisms of starch, sucrose, carbon, and glutathione. The chloroplasts in Az34 leaves were more severely damaged, and the decrease in Fv/Fm was larger in Az34 plants compared with WT under low temperature. Under low temperature, Az34 plants possessed significantly higher activities of ADP-glucose pyrophosphorylase, fructokinase, monodehydroascorbate reductase, and three invertases, but lower UDP-glucose pyrophosphorylase activity than WT. In addition, concentrations of proline and soluble protein were lower, while concentration of H2O2 was higher in Az34 plants compared to WT under low temperature. Collectively, the results indicated that ABA deficiency induced modifications in starch and sucrose biosynthesis and sucrolytic pathway and overaccumulation of reactive oxygen species were the main reason for depressed low temperature tolerance in barley, which provide novel insights to the response of barley to low temperature under future climate change."
Authors: Meng-Chun Lin, I-Chieh Tseng, Ching-Lan Wang, Wen-Rong Hsiao, Yun-Jhih Shih, Wen-Dar Lin, Su-May Yu and Tuan-hua David Ho.
bioRxiv (2023)
Abstract: "Water deficit stress causes devastating loss of crop yield worldwide. Improving crop drought resistance has become an urgent issue. Here we report that a group of abscisic acid (ABA)/drought stress-induced monocot-specific, intrinsically disordered, and highly proline-rich proteins, REPETITIVE PROLINE-RICH PROTEINS (RePRPs), play pivotal roles in drought resistance in rice seedlings. Rice ectopically expressing RePRPs outlived wild-type rice under extreme drought conditions primarily due to two underlying mechanisms. First, RePRP reduces water loss by decreasing stomata conductance in shoot. In addition, RePRP overexpression enhances the levels of extracellular water barriers such as lignin and suberin, primarily in the root vascular bundle. Several groups of genes involved in lignin biosynthesis, especially the wall-bound peroxidase responsible for the final assembly of the lignin network, were induced by RePRP. Second, overexpression of RePRP leads to lowered root osmotic potential. Root cell osmotic pressure was more negative in rice plants overexpressing RePRP2 than wild-type plants, and the concentration of a key osmolyte, proline, was enhanced. Furthermore, the protein levels of two aquaporins that are important for drought stress tolerance were elevated. Hence, ABA/stress-induced RePRP expression leads to several beneficial traits of drought resistance, including lower water loss rate upon dehydration and higher root water use efficiency under drought conditions. This group of unique stress proteins may be an important target for technology development in enhancing drought stress resistance in cereals."
Authors: Fumiyuki Soma, Fuminori Takahashi, Satoshi Kidokoro, Haruka Kameoka, Takamasa Suzuki, Yusaku Uga, Kazuo Shinozaki and Kazuko Yamaguchi-Shinozaki.
PNAS (2023)
Significance The phytohormone ABA plays important roles in drought stress responses. Although subclass III SnRK2s, key regulators of ABA signaling, have been thought to be self-activated by autophosphorylation, they were reported to be activated by two subfamilies of group B Raf-like kinases, B2-RAFs and B3-RAFs, under drought stress. However, the relationship between SnRK2 phosphorylation by individual RAFs and SnRK2 autophosphorylation remains unknown. We revealed that B2-RAF RAF11 is constantly active and activates SnRK2s when released from PP2C-mediated inhibition, whereas B3-RAF RAF5 is activated under stress conditions. Thus, SnRK2 autophosphorylation is not sufficient for ABA responses, and B2-RAFs are essential for SnRK2 activation in response to ABA under mild drought, whereas B3-RAFs function as enhancers of SnRK2 activity under severe osmotic stress.
Abstract: "Osmotic stresses, such as drought and high salinity, adversely affect plant growth and productivity. The phytohormone abscisic acid (ABA) accumulates in response to osmotic stress and enhances stress tolerance in plants by triggering multiple physiological responses through ABA signaling. Subclass III SNF1–related protein kinases 2 (SnRK2s) are key regulators of ABA signaling. Although SnRK2s have long been considered to be self-activated by autophosphorylation after release from PP2C-mediated inhibition, they were recently revealed to be activated by two independent subfamilies of group B Raf-like kinases, B2-RAFs and B3-RAFs, under osmotic stress conditions. However, the relationship between SnRK2 phosphorylation by these RAFs and SnRK2 autophosphorylation and the individual physiological roles of each RAF subfamily remain unknown. In this study, we indicated that B2-RAFs are constantly active and activate SnRK2s when released from PP2C-mediated inhibition by ABA-binding ABA receptors, whereas B3-RAFs are activated only under stress conditions in an ABA-independent manner and enhance SnRK2 activity. Autophosphorylation of subclass III SnRK2s is not sufficient for ABA responses, and B2-RAFs are needed to activate SnRK2s in an ABA-dependent manner. Using plants grown in soil, we found that B2-RAFs regulate subclass III SnRK2s at the early stage of drought stress, whereas B3-RAFs regulate SnRK2s at the later stage. Thus, B2-RAFs are essential kinases for the activation of subclass III SnRK2s in response to ABA under mild osmotic stress conditions, and B3-RAFs function as enhancers of SnRK2 activity under severe stress conditions."
Authors: Zhi-Xin Xiang, Wen Li, Ying-Tang Lu and Ting-Ting Yuan.
The Plant Journal (2023)
Abstract: "Hydrogen sulfide (H2S) promotes plant tolerance against various environmental cues, and D-cysteine desulfhydrase (DCD) is an enzymatic source of H2S to enhance abiotic stress resistance. However, the role of DCD-mediated H2S production in root growth under abiotic stress remains to be further elucidated. Here, we reported that DCD-mediated H2S production alleviates osmotic stress-mediated root growth inhibition via promoting auxin homeostasis. Osmotic stress up-regulated DCD gene transcript and DCD protein levels, thus H2S production in roots. When subjected to osmotic stress, a dcd mutant showed more severe root growth inhibition, whereas the transgenic lines DCDox overexpressing DCD exhibited less sensitivity to osmotic stress in terms of longer root compared with the wild type. Moreover, osmotic stress inhibited root growth through repressing auxin signaling, but H2S treatment significantly alleviated osmotic stress-mediated inhibition of auxin. Under osmotic stress, auxin accumulation was increased in DCDox but decreased in dcd mutant. H2S promoted auxin biosynthesis genes expressions and auxin efflux carrier PIN-FORMED 1 (PIN1) protein level under osmotic stress. Together, our results revealed that mannitol-induced DCD and H2S in roots promote auxin homeostasis, contributing to alleviating the inhibition of root growth under osmotic stress."
Authors: Riddhi Datta, Ananya Roy and Soumitra Paul.
In book: Plant Hormones and Crop Improvement; edited by M. Iqbal R. Khan, Amarjeet Singh and Péter Poór (2023)
Abstract: "With the changing environmental condition, coping with abiotic stress factors has become a major challenge for plants. Among them, drought and salinity pose serious threats to plant survival. To counter this, plants have evolved an intricate signaling network where phytohormones are the key players. In response to osmotic stress, different signaling cues trigger the synthesis of the stress hormone abscisic acid (ABA) and hinder the growth hormone gibberellic acid (GA) thus lowering the GA/ABA ratio and stabilizing the DELLA repressor. This leads to growth restrain and promotes stress-adaptive phenomena like stomatal closure, ion homeostasis, and inhibition of seed germination signifying transition from “growth phase” to “defense phase.” Ethylene, brassinosteroids, jasmonic acid, salicylic acid, and strigolactones facilitate these phenomena, while cytokinin antagonizes the ABA-mediated responses. Auxin again regulates lateral root growth and halotropism under stress. This chapter also highlights the application of phytohormones to enhance tolerance and crop productivity under osmotic stress."
Authors: Yeongil Bae, Chae Woo Lim and Sung Chul Lee.
The Plant Journal (2022)
Abstract: "The phytohormone abscisic acid (ABA) plays a prominent role in various abiotic stress responses of plants. In the ABA-dependent osmotic stress response, SnRK2.6, one of the subclass lll SnRK2 kinases, has been identified as playing a key role by phosphorylating and activating downstream genes. Although several regulatory proteins have been reported to be phosphorylated by SnRK2.6, the identities of the full spectrum of downstream targets have yet to be sufficiently established. In this study, we identified CaSAP14, a stress-associated protein in pepper (Capsicum annuum), as a downstream target of CaSnRK2.6. We elucidated the physical interaction between SnRK2.6 and CaSAP14, both in vitro and in vivo, and accordingly identified a C-terminal C2H2-type zinc finger domain of CaSAP14 as being important for their interaction. CaSAP14-silenced pepper plants showed dehydration- and high salt-sensitive phenotypes, whereas overexpression of CaSAP14 in Arabidopsis conferred tolerance to dehydration, high salinity, and mannitol treatment, with plants showing ABA-hypersensitive phenotypes. Furthermore, an in-gel kinase assay revealed that CaSnRK2.6 phosphorylates CaSAP14 in response to exogenous ABA, dehydration, and high-salinity stress. Collectively, these findings suggest that CaSAP14 is a direct substrate of CaSnRK2.6 and positively modulates dehydration- and high salinity-induced osmotic stress responses."
Authors: Yanyang Zhang, Yingjia Zhao, Tianjiao Li, Chenyang Ni, Le Han, Pingping Du and Kai Xiao.
BMC Plant Biology (2022)
Abstract: "Background - Abscisic acid receptors (ABR) involve transduction of the ABA signaling in plants, impacting largely on stress-defensive physiological processes and plant osmotic stress response. In this study, we characterized TaPYL4, a gene of ABR family in T. aestivum, in mediating plant drought tolerance given scarcity of functional characterization on wheat ABR members thus far. Results - TaPYL4 harbors nine conserved domains shared by its PYL counterparts, targeting onto plasma membrane and nucleus after endoplasmic reticulum assortment. TaPYL4 interacts with TaPP2C2 whereas the latter with TaSnRK2.1, which establish a core module of the ABA signaling pathway. TaPYL4 expression was upregulated in root and aerial tissues upon drought stress. Overexpressing TaPYL4 conferred plants improved growth traits whereas knockdown expression of target gene alleviated growth feature compared with wild type under drought treatment. The TaPYL4-enhanced drought adaptation associates gene function in positively regulating stomata movement, osmolyte biosynthesis, and root system architecture (RSA) establishment. Expression analysis on the P5CS family genes involving proline biosynthesis indicated that TaP5CS1 exerts critical roles in promoting osmolytes accumulation in drought-challenged TaPYL4 lines. TaPIN9, a PIN-FORMED gene modulating cellular auxin translocation, was validated to function as a crucial mediator in defining RSA establishment underlying TaPYL4 regulation. Transcriptome analysis revealed that TaPYL4 controls transcription of numerous genes, which impact on physiological processes associated with ‘biological process’, ‘molecular component’, and ‘cellular process’. Moreover, the differentially expressed genes mediated by TaPYL4 were closely related to stress defensive pathways. Conclusions - Our investigation suggested that TaPYL4 acts as a positive regulator in plant drought tolerance and a valuable target for engineering drought-tolerant cultivars in T. aestivum."
Authors: Leelyn Chong, Chuan-Chih Hsu and Yingfang Zhu.
Journal of Experimental Botany (2022)
Abstract: "Abiotic stresses have significant influences on crop yield and quality. Even though significant efforts have been devoted to excavating the core signaling pathways associated with the phytohormone abscisic acid (ABA) and abiotic stress in plants during the past decade, abiotic stress signaling mechanisms in most crops remain largely unclear. The core components of ABA signaling pathway including early events in the osmotic stress-induced phosphorylation network have been elucidated in Arabidopsis recently with the aid of phosphoproteomics technologies. We now know that SNF1-related kinases 2 (SnRK2s) are not only inhibited by the clade A type 2C protein phosphatases (PP2Cs) through dephosphorylation, but also are phosphorylated and activated by upstream mitogen-activated protein kinase kinase kinases (MAP3Ks). Through recounting a journey of abiotic stress and ABA signaling excavations, we will discuss why we can take advantage of the latest innovations in mass spectrometry-based phosphoproteomics and structural proteomics to boost our investigation of plant regulation and response to ABA and abiotic stress."
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Authors: Yuwen Zhang, Xingliang Duan, Yuanming Xie and Wei Xuan.
New Crops (2024)
Abstract: "Plant root systems are critical for absorbing water and nutrients and anchoring plants in the soil, and their development is regulated by phytohormones and complex signaling pathways. Recent studies have identified small peptides as essential players in governing root development, binding to specific receptors on the cell membrane, and triggering signaling processes. In this study, we summarize recent advances in small peptide regulation of root system architecture and tissue organization, as well as the molecular interaction between peptides and canonical hormone signaling. Additionally, we discuss the functions of small peptides in modulating root development responses to environmental forces like nitrogen and phosphate starvation, osmotic stress, and soil microbes through the activation of local and systemic signaling pathways. This review offers a comprehensive overview of peptide signaling during plant root development and prospects for further crop breeding applications."
Authors: Jasper Lamers, Yanxia Zhang, Eva van Zelm, A. Jessica Meyer, Thijs de Zeeuw, Francel Verstappen, Mark Veen, Ayodeji O. Deolu-Ajayi, Charlotte M.M. Gommers and Christa Testerink.
bioRxiv (2023)
Abstract: "Soil salinity presents a dual challenge for plants, involving both osmotic and ionic stress. In response, plants deploy distinct yet interconnected mechanisms to cope with these facets of salinity stress. In this investigation, we observed a substantial overlap in the salt (NaCl)-induced transcriptional responses of Arabidopsis roots with those triggered by osmotic stress or the plant stress hormone abscisic acid (ABA), as anticipated. Notably, a specific cluster of genes responded uniquely to sodium (Na+) ions. Surprisingly, expression of sodium-induced genes exhibited a negative correlation with the ABA response and preceded the activation of genes induced by the osmotic stress component of salt. Elevated exogenous ABA levels resulted in the complete abolition of sodium-induced responses. Consistently, ABA signalling mutants displayed prolonged sodium-induced gene expression, coupled with increased root cell damage under high salinity conditions. Moreover, ABA signalling mutants were unable to redirect root growth to avoid high sodium concentrations and failed to contain their root cell swelling in the presence of elevated salt levels. In summary, our findings unveil an unexpected and pivotal role for ABA signaling in mitigating cellular damage induced by salinity stress and modulating sodium-specific responses in plant roots."
Authors: Jia Li, Xinyi Liu, Naveed Ahmad, Yifei Wang, Hengshuo Ge, Yijin Wang, Weican Liu, Xiaowei Li, Nan Wang, Fawei Wang and Yuanyuan Dong.
BMC Plant Biology (2023)
Abstract: "Background - Tiger nut (Cyperus esculentus) is widely known as an additional source of food, oil and feed worldwide. The agricultural production of tiger nut has been greatly hindered by drought stress, reducing both yield and quality. Protein phosphatase 2 C (PP2Cs) plays an important role in plant responses to drought stress however, the molecular mechanism of PP2Cs in tiger nuts still unclear. Results - In this study, we identified a putative group A PP2C-encoding gene (CePP2C19) from tiger nut using transcriptome analysis, which is highly induced by drought stress. The transient expression assay suggested that CePP2C19 was localized to nucleus. Furthermore, the interaction between CePP2C19 and CePYR1, a coreceptor for ABA signaling, was first detected using a yeast two-hybrid assay and then verified using a bimolecular fluorescence complementation (BiFC) analysis. In addition, the transgenic Arabidopsis lines overexpressing CePP2C19 exhibited extreme tolerance to ABA and mannitol stresses during seed germination and root growth. At the mature stage, overexpression of CePP2C19 resulted in a higher tolerance to drought stress in transgenic Arabidopsis, as confirmed by a visible phenotype and several physiological parameters. Noticeably, the silencing of CePP2C19 by virus-induced gene silencing (VIGS) showed obvious reduction in drought tolerance in tiger nut plants. Conclusions - The CePP2C19 emerges as a pivotal gene involved in the ABA signaling pathway, which likely reduce ABA sensitivity and thus enhances drought tolerance in Cyperus esculentus."
Authors: Takuya Yoshida and Alisdair R. Fernie
Journal of Experimental Botany (2024)
Abstract: "Phytohormones are essential signaling molecules globally regulating many processes of plants, including their growth, development and stress responses. The promotion of growth and the enhancement of stress resistance have to be balanced, especially under adverse conditions such as drought stress, because of limited resources. Plants cope with drought stress via various strategies, including the transcriptional regulation of stress-responsive genes and the adjustment of metabolism, and phytohormones play roles in these processes. However, besides abscisic acid (ABA) is an important signal under drought, less attention has been paid to other phytohormones. In this review, we summarize progress in the understanding of phytohormone-regulated primary metabolism under water-limited conditions, especially in Arabidopsis thaliana, and highlight recent findings concerning the amino acids associated with ABA metabolism and signaling. We also discuss how phytohormones function antagonistically and synergistically in order to balance growth and stress responses."
Authors: Lin Zheng, Yajuan Chen, Liping Ding, Ying Zhou, Shanshan Xue, Biying Li, Jianhua Wei and Hongzhi Wang.
The Plant Cell (2023)
Abstract: "The mechanical properties of guard cells have major effects on stomatal functioning. Reinforced stiffness in the stomatal polar regions was recently proposed to play an important role in stomatal function, but the underlying molecular mechanisms remain elusive. Here, we used genetic and biochemical approaches in poplar (Populus spp.) to show that the transcription factor MYB156 controls pectic homogalacturonan-based polar stiffening through the downregulation of the gene encoding pectin methylesterase 6 (PME6). Loss of MYB156 increased the polar stiffness of stomata, thereby enhancing stomatal dynamics and response speed to various stimuli. In contrast, overexpression of MYB156 resulted in decreased polar stiffness and impaired stomatal dynamics, accompanied by smaller leaves. Polar stiffening functions in guard cell dynamics in response to changing environmental conditions by maintaining normal stomatal morphology during stomatal movement. Our study revealed the structure-function relationship of the cell wall of guard cells in stomatal dynamics, providing an important means for improving the stomatal performance and drought tolerance of plants."
Authors: Tai S. Chiriotto, Maite Saura-Sánchez, Carla Barraza and Javier F. Botto.
Plants (2023)
Abstract: "Seed germination is a critical stage for survival during the life cycle of an individual plant. Genetic and environmental cues are integrated by individual seeds to determine germination, mainly achieved through regulation of the metabolism and signaling of gibberellins (GA) and abscisic acid (ABA), two phytohormones with antagonistic roles. Saline and drought conditions can arrest the germination of seeds and limit the seedling emergence and homogeneity of crops. This work aimed to study the function of BBX24, a B-Box transcription factor, in the control of germination of Arabidopsis thaliana seeds imbibed in saline and osmotic conditions. Seeds of mutant and reporter GUS lines of BBX24 were incubated at different doses of NaCl and polyethylene-glycol (PEG) solutions and with ABA, GA and their inhibitors to evaluate the rate of germination. We found that BBX24 promotes seed germination under moderated stresses. The expression of BBX24 is inhibited by NaCl and PEG. In addition, ABA suppresses BBX24-induced seed germination. Additional experiments suggest that BBX24 reduces ABA sensitivity, improving NaCl tolerance, and increases GA sensitivity in seeds imbibed in ABA. In addition, BBX24 inhibits the expression of ABI3 and ABI5 and genetically interacts upstream of HY5 and ABI5. This study demonstrates the relevance of BBX24 to induce drought and salinity tolerance in seed germination to ensure seedling emergence in sub-optimal environments."
Authors: Yibin Wang, Gaofeng Zhang, Huimin Zhou, Shanshan Yin, Yunxiang Li, Caixia Ma, Pengyun Chen, Lirong Sun and Fushun Hao.
BMC Plant Biology (2023)
Abstract: "Background - Abscisic acid (ABA) receptor pyrabactin resistance 1/PYR1-like/regulatory components of ABA receptor proteins (PYR/PYL/RCARs) have been demonstrated to play pivotal roles in ABA signaling and in response to diverse environmental stimuli including drought, salinity and osmotic stress in Arabidopsis. However, whether and how GhPYL9-5D and GhPYR1-3A, the homologues of Arabidopsis PYL9 and PYR1 in cotton, function in responding to ABA and abiotic stresses are still unclear. Results - GhPYL9-5D and GhPYR1-3A were targeted to the cytoplasm and nucleus. Overexpression of GhPYL9-5D and GhPYR1-3A in Arabidopsis wild type and sextuple mutant pyr1pyl1pyl2pyl4pyl5pyl8 plants resulted in ABA hypersensitivity in terms of seed germination, root growth and stomatal closure, as well as seedling tolerance to water deficit, salt and osmotic stress. Moreover, the VIGS (Virus-induced gene silencing) cotton plants, in which GhPYL9-5D or GhPYR1-3A were knocked down, showed clearly reduced tolerance to polyethylene glycol 6000 (PEG)-induced drought, salinity and osmotic stresses compared with the controls. Additionally, transcriptomic data revealed that GhPYL9-5D was highly expressed in the root, and GhPYR1-3A was strongly expressed in the fiber and stem. GhPYL9-5D, GhPYR1-3A and their homologs in cotton were highly expressed after treatment with PEG or NaCl, and the two genes were co-expressed with redox signaling components, transcription factors and auxin signal components. These results suggest that GhPYL9-5D and GhPYR1-3A may serve important roles through interplaying with hormone and other signaling components in cotton adaptation to salt or osmotic stress. Conclusions - GhPYL9-5D and GhPYR1-3A positively regulate ABA-mediated seed germination, primary root growth and stomatal closure, as well as tolerance to drought, salt and osmotic stresses likely through affecting the expression of multiple downstream stress-associated genes in Arabidopsis and cotton.
Authors: Chunmei Yin, Aiqing Sun, Ying Zhou, Kunpeng Liu, Pan Wang, Wenjing Ye and Yuda Fang.
Journal of Experimental Botany (2023)
Abstract: "Extreme environmental changes threaten plant survival and worldwide food production. In response to osmotic stresses, plant hormone ABA activates stress responses and restricts plant growth. However, the epigenetic regulation of the ABA signaling and ABA-auxin crosstalk are not well known. Here we report that the histone variant H2A.Z knockdown mutant in Arabidopsis Col-0 ecotype, h2a.z-kd, has altered ABA signaling and stress performances. RNA-sequencing data showed that a majority of stress related genes are activated in h2a.z-kd. In addition, we revealed that ABA directly promotes the deposition of H2A.Z on SMALL AUXIN UP RNAs (SAURs), which is involved in ABA-repressed SAUR expression. Moreover, we found that ABA represses the transcription of H2A.Z genes through suppressing ARF7/19-HB22/25 module. Our results shed light on a dynamic and reciprocal regulation hub through H2A.Z deposition on SAURs and ARF7/19-HB22/25-mediated H2A.Z transcription to integrate ABA/auxin signaling and regulate stress responses in Arabidopsis."
Authors: Xinkai Jin, Yifan Zhang, Xingxing Li and Junli Huang.
The Plant Journal (2023)
Abstract: "The antagonism between gibberellin (GA) and abscisic acid (ABA) signaling pathways is vital to balance plant growth and stress response. Nevertheless, the mechanism by which plants determine the balance remains to be elucidated. Here, we report that rice NUCLEAR FACTOR-Y A3 (OsNF-YA3) modulates GA- and ABA-mediated balance between plant growth and osmotic stress tolerance. OsNF-YA3 loss-of-function mutants exhibit stunted growth, compromised GA biosynthetic gene expression, and decreased GA levels, while its overexpression lines have promoted growth and enhanced GA content. ChIP-qPCR analysis and transient transcriptional regulation assays demonstrate that OsNF-YA3 activates GA biosynthetic gene OsGA20ox1 expression. Furthermore, the DELLA protein SLENDER RICE1 (SLR1) physically interacts with OsNF-YA3 and thus inhibits its transcriptional activity. On the other side, OsNF-YA3 negatively regulates plant osmotic stress tolerance by repressing ABA response. OsNF-YA3 reduces ABA levels by transcriptionally regulating ABA catabolic genes OsABA8ox1 and OsABA8ox3 by binding to their promoters. Furthermore, OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 9 (SAPK9), the positive component in ABA signaling, interacts with OsNF-YA3 and mediates OsNF-YA3 phosphorylation, resulting in its degradation in plants. Collectively, our findings establish OsNF-YA3 as an important transcription factor that positively modulates GA-regulated plant growth and negatively controls ABA-mediated water-deficit and salt tolerance. These findings shed light on the regulatory mechanism underlying the balance between the growth and stress response of the plant."
Authors: Guzel Akhiyarova, Dmitriy Veselov, Ruslan Ivanov, Guzel Sharipova, Igor Ivanov, Ian C. Dodd and Guzel Kudoyarova.
International Journal of Plant Biology (2023)
Abstract: "Increased auxin levels in root primordia are important in controlling root branching, while their interaction with abscisic acid (ABA) likely regulates lateral root development in water-deficient plants. The role of ABA accumulation in regulating root branching was investigated using immunolocalization to detect auxin (indoleacetic acid, IAA) and ABA (abscisic acid) in root primordia of the ABA-deficient barley mutant Az34 and its parental genotype (cv. Steptoe) barley plants. Osmotic stress strongly inhibited lateral root branching in Steptoe plants, but hardly affected Az34. Root primordial cells of Steptoe plants had increased immunostaining for ABA but diminished staining for IAA. ABA did not accumulate in root primordia of the Az34, and IAA levels and distribution were unaltered. Treating Az34 plants with exogenous ABA decreased root IAA concentration, while increasing root primordial ABA accumulation and decreasing root primordial IAA concentration. Although ABA treatment of Az34 plants increased the root primordial number, it decreased the number of visible emerged lateral roots. These effects were qualitatively similar to that of osmotic stress on the number of lateral root primordia and emerged lateral roots in Steptoe. Thus ABA accumulation (and its crosstalk with auxin) in root primordia seems important in regulating lateral root branching in response to water stress."
Authors: Marta Trasoletti, Ivan Visentin, Eva Campo, Andrea Schubert and Francesca Cardinale.
Plant, Cell & Environment (2022)
Abstract: "Strigolactones are phytohormones with many attributed roles in development, and more recently in responses to environmental stress. We will review evidence of the latter in the frame of the classic distinction among the three main stress acclimation strategies (i.e. avoidance, tolerance, and escape), by taking osmotic stress in its several facets as a non-exclusive case study. The picture we will sketch is that of a hormonal family playing important roles in each of the mechanisms tested so far, and influencing as well the build-up of environmental memory through priming. Thus, strigolactones appear to be backstage operators rather than frontstage players, setting the tune of acclimation responses by fitting them to the plant individual history of stress experience."
Authors: Mohammad Golam Mostofa, Mostafa Abdelrahman, Md. Mezanur Rahman, Cuong Duy Tran, Kien Huu Nguyen, Yasuko Watanabe, Misao Itouga, Weiqiang Li, Zhe Wang, Keiichi Mochida and Lam-Son Phan Tran.
Plant and Cell Physiology (2022)
Abstract: "Plants activate a myriad of signaling cascades to tailor adaptive responses under environmental stresses, such as salinity. While the roles of exogenous karrikins (KARs) in salt stress mitigation are well comprehended, genetic evidence of KAR signaling during salinity responses in plants remains unresolved. Here, we explored the functions of the possible KAR receptor KARRIKIN INSENSITIVE2 (KAI2) in Arabidopsis thaliana resistance to salt stress by investigating comparative responses of wild-type (WT) and kai2 mutant plants under a gradient of NaCl. Defect in KAI2 functions resulted in delayed and inhibited cotyledon opening in kai2 seeds compared with WT seeds, suggesting that KAI2 played an important role in enhancing seed germination under salinity. Salt-stressed kai2 plants displayed more phenotypic aberrations, biomass reduction, water loss and oxidative damage than WT plants. kai2 shoots accumulated significantly more Na+, and thus had a lower K+/Na+ ratio, than WT, indicating a severe ion-toxicity in salt-stressed kai2 plants. Accordingly, kai2 plants displayed lower expression of the genes associated with Na+ homeostasis, such as SALT OVERLY SENSITIVE (SOS) 1, SOS2, HIGH AFFINITY POTASSIUM TRANSPORTER 1;1 (HKT1;1) and CATION-HYDROGEN EXCHANGER 1 (NHX1) than WT plants. WT plants maintained a better status of glutathione level, glutathione-related redox status and antioxidant enzyme activities relative to kai2 plants, implying KAI2’s function in oxidative stress mitigation in response to salinity. kai2 shoots had lower expression levels of the genes involved in the biosynthesis of strigolactones, salicylic acid and jasmonic acid, and the signaling of abscisic acid and strigolactones than those of WT plants, indicating interactive functions of KAI2 signaling with other hormone signaling in modulating plant responses to salinity. Collectively, these results underpin the likely roles of KAI2 in alleviation of salinity effects in plants by regulating several physiological and biochemical mechanisms involved in ionic and osmotic balance, oxidative stress tolerance and hormonal crosstalk."
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