AtPR5K2, a PR5-Like Receptor Kinase, Modulates Plant Responses to Drought Stress by Phosphorylating Protein Phosphatase 2Cs.
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ABSTRACT: Cell surface receptors perceive signals from the environment and transfer them to the interior of the cell. The Arabidopsis thaliana PR5 receptor-like kinase (AtPR5K) subfamily consists of three members with extracellular domains that share sequence similarity with the PR5 proteins. In this study, we characterized the role of AtPR5K2 in plant drought-stress signaling. AtPR5K2 is predominantly expressed in leaves and localized to the plasma membrane. The atpr5k2-1 mutant showed tolerance to dehydration stress, while AtPR5K2-overexpressing plants was hypersensitive to drought. Bimolecular fluorescence complementation assays showed that AtPR5K2 physically interacted with the type 2C protein phosphatases ABA-insensitive 1 (ABI1) and ABI2 and the SNF1-related protein kinase 2 (SnRK2.6) proteins, all of which are involved in the initiation of abscisic acid (ABA) signaling; however, these interactions were inhibited by treatments of exogenous ABA. Moreover, AtPR5K2 was found to phosphorylate ABI1 and ABI2, but not SnRK2.6. Taken together, these results suggest that AtPR5K2 participates in ABA-dependent drought-stress signaling through the phosphorylation of ABI1 and ABI2.
Project description:Pyrophosphate (PPi), a byproduct of macromolecule biosynthesis is maintained at low levels by soluble inorganic pyrophosphatases (sPPase) found in all eukaryotes. In plants, H+-pumping pyrophosphatases (H+-PPase) convert the substantial energy present in PPi into an electrochemical gradient. We show here, that both cold- and heat stress sensitivity of fugu5 mutants lacking the major H+-PPase isoform AVP1 is correlated with reduced SUMOylation. In addition, we show that increased PPi concentrations interfere with SUMOylation in yeast and we provide evidence that SUMO activating E1-enzymes are inhibited by micromolar concentrations of PPi in a non-competitive manner. Taken together, our results do not only provide a mechanistic explanation for the beneficial effects of AVP1 overexpression in plants but they also highlight PPi as an important integrator of metabolism and stress tolerance.
Project description:Down-regulation of reactive oxygen species build-up in chloroplasts by expression of a plastid-targeted flavodoxin protects potato leaves under drought conditions. To better understand these effects we compared the transcriptomic alterations in a pre-symtomatic stage of drought treatment on leaves of Fld-expressing potato plants and their wild-type siblings.
Project description:E3 ligases play significant roles in plant stress tolerance by targeting specific substrate proteins for post-translational modification. In a previous study, we cloned TaPUB1 from Triticum aestivum L., which encodes a U-box E3 ligase. Real-time polymerase chain reaction revealed that the gene was up-regulated under drought stress. To investigate the function of TaPUB1 in the response of plants to drought, we generated transgenic Nicotiana benthamiana (N. benthamiana) plants constitutively expressing TaPUB1 under the CaMV35S promoter. Compared to wild type (WT), the transgenic plants had higher germination and seedling survival rates as well as higher photosynthetic rate and water retention, suggesting that the overexpression of TaPUB1 enhanced the drought tolerance of the TaPUB1 overexpressing (OE) plants. Moreover, less accumulation of reactive oxygen species (ROS) and stronger antioxidant capacity were detected in the OE plants than in the WT plants. To characterize the mechanisms involved, methyl viologen (MV) was used to induce oxidative stress conditions and we identified the functions of this gene in the plant tolerance to oxidative stress. Our results suggest that TaPUB1 positively modulates plant drought stress resistance potential by improving their antioxidant capacity.
Project description:Phosphatase plays a crucial role in determining cellular fate by inactivating its substrate kinase, but it is not known whether a kinase can vice versa phosphorylate its phosphatase to execute this function. Protein-tyrosine phosphatase H1 (PTPH1) is a specific phosphatase of p38? mitogen-activated protein kinase (MAPK) through PDZ binding, and here, we show that p38? is also a PTPH1 kinase through which it executes its oncogenic activity and regulates stress response. PTPH1 was identified as a substrate of p38? by unbiased proteomic analysis, and its resultant phosphorylation at Ser-459 occurs in vitro and in vivo through their complex formation. Genetic and pharmacological analyses showed further that Ser-459 phosphorylation is directly regulated by Ras signaling and is important for Ras, p38?, and PTPH1 oncogenic activity. Moreover, experiments with physiological stimuli revealed a novel stress pathway from p38? to PTPH1/Ser-459 phosphorylation in regulating cell growth and cell death by a mechanism dependent on cellular environments but independent of canonical MAPK activities. These results thus reveal a new mechanism by which a MAPK regulates Ras oncogenesis and stress response through directly phosphorylating its phosphatase.
Project description:Protein phosphorylation and dephosphorylation are important mechanisms that regulate many cellular processes. Protein kinases usually function in the regulation of the stress responses by adjusting activity via phosphorylation of target proteins. Here, we isolated CaAIMK1 (Capsicum annuum ABA Induced MAP Kinase 1) from the pepper leaves that had been subjected to drought stress. CaAIMK1 transcripts were induced by drought, abscisic acid (ABA), high salinity, and H2O2; further, the CaAIMK1-Green fluorescent protein localized in the nucleus and cytoplasm. We performed genetic studies using CaAIMK1-silenced pepper plants and CaAIMK1-overexpressing (OX) Arabidopsis plants. CaAIMK1-silenced pepper plants showed a drought-sensitive phenotype characterized by altered ABA signaling, including low leaf temperatures, and large stomatal apertures. CaAIMK1-OX plants exhibited a contrasting drought-tolerant phenotype characterized by decreased levels of transpirational water loss and increased expression levels of Arabidopsis stress-related genes. In CaAIMK1 K32N-OX transgenic Arabidopsis plants, sensitivity to ABA and drought was restored. Collectively, these results demonstrate that CaAIMK1 positively regulates the drought stress responses via an ABA-dependent pathway.
Project description:This report provides direct evidence that strigolactone (SL) positively regulates drought and high salinity responses in Arabidopsis. Both SL-deficient and SL-response [more axillary growth (max)] mutants exhibited hypersensitivity to drought and salt stress, which was associated with shoot- rather than root-related traits. Exogenous SL treatment rescued the drought-sensitive phenotype of the SL-deficient mutants but not of the SL-response mutant, and enhanced drought tolerance of WT plants, confirming the role of SL as a positive regulator in stress response. In agreement with the drought-sensitive phenotype, max mutants exhibited increased leaf stomatal density relative to WT and slower abscisic acid (ABA)-induced stomatal closure. Compared with WT, the max mutants exhibited increased leaf water loss rate during dehydration and decreased ABA responsiveness during germination and postgermination. Collectively, these results indicate that cross-talk between SL and ABA plays an important role in integrating stress signals to regulate stomatal development and function. Additionally, a comparative microarray analysis of the leaves of the SL-response max2 mutant and WT plants under normal and dehydrative conditions revealed an SL-mediated network controlling plant responses to stress via many stress- and/or ABA-responsive and cytokinin metabolism-related genes. Our results demonstrate that plants integrate multiple hormone-response pathways for adaptation to environmental stress. Based on our results, genetic modulation of SL content/response could be applied as a potential approach to reduce the negative impact of abiotic stress on crop productivity.
Project description:BACKGROUND:The calcineurin B-like protein (CBL)-interacting protein kinase (CIPK) signaling pathway responds to various abiotic stresses in plants. RESULTS:Wheat CIPK23, isolated from wheat drought transcriptome data set, was induced by multiple abiotic stresses, including drought, salt, and abscisic acid (ABA). Compared with wild-type plants, TaCIPK23-overexpression wheat and Arabidopsis showed an higher survival rate under drought conditions with enhanced germination rate, developed root system, increased accumulation of osmolytes, and reduced water loss rate. Over-expression of TaCIPK23 rendered transgenic plants ABA sensitivity, as evidenced by delayed seed germination and the induction of stomatal closure. Consistent with the ABA-sensitive phenotype, the expression level of drought- and ABA-responsive genes were increased under drought conditions in the transgenic plants. In addition, using yeast two-hybrid system, pull-down and bimolecular fluorescence complementation (BiFc) assays, TaCIPK23 was found to interact with TaCBL1 on the plasma membrane. CONCLUSIONS:These results suggest that TaCIPK23 plays important roles in ABA and drought stress responses, and mediates crosstalk between the ABA signaling pathway and drought stress responses in wheat.
Project description:We examined the effect of soil microbial communities on plant physiological responses to drought. Bouteloua gracilis seeds were planted in sterilized sand with (inoculated) and without (controls) soil microbial communities. After substantial growth, drought was imposed by completely withholding water. Before soil moisture declined to zero, inoculated plants germinated faster, were significantly taller, and maintained greater soil moisture than controls. The greater soil moisture of the inoculated plants allowed greater photosynthesis but also induced lower tissue drought tolerance (as indicated by turgor loss point) compared to controls. The inoculated plants were more susceptible to severe drought compared to control plants as indicated by significantly lower mean stomatal conductance, as well as marginally significantly greater mean wilting score, for the entire severe drought period after soil moisture declined to zero. Inoculated plants exhibited enhanced growth and photosynthesis and dampened drought stress over short timescales, but also increased susceptibility to drought over long timescales. This work demonstrates (1) an unexpected insight that microbes can have positive initial effects on plant performance, but negative impacts on plant performance during severe drought, and (2) that microbially altered effects on plant function during well-watered and moderate drought conditions can influence plant function under subsequent severe drought.
Project description:Several nucleoporins in the nuclear pore complex (NPC) have been reported to be involved in abiotic stress responses in plants. However, the molecular mechanism of how NPC regulates abiotic stress responses, especially the expression of stress responsive genes remains poorly understood. From a forward genetics screen using an abiotic stress-responsive luciferase reporter (RD29A-LUC) in the sickle-1 (sic-1) mutant background, we identified a suppressor caused by a mutation in NUCLEOPORIN 85 (NUP85), which exhibited reduced expression of RD29A-LUC in response to ABA and salt stress. Consistently, the ABA and salinity induced expression of several stress responsive genes such as RD29A, COR15A and COR47 was significantly compromised in nup85 mutants and other nucleoporin mutants such as nup160 and hos1. Subsequently, Immunoprecipitation and mass spectrometry analysis revealed that NUP85 is potentially associated with HOS1 and other nucleoporins within the nup107-160 complex, along with several mediator subunits. We further showed that there is a direct physical interaction between MED18 and NUP85. Similar to NUP85 mutations, MED18 mutation was also found to attenuate expression of stress responsive genes. Taken together, we not only revealed the involvement of NUP85 and other nucleoporins in regulating ABA and salt stress responses, but also uncovered a potential relation between NPC and mediator complex in modulating the gene expression in plants.
Project description:In response to drought stress the phytohormone ABA (abscisic acid) induces stomatal closure and, therein, activates guard cell anion channels in a calcium-dependent as well as-independent manner. Two key components of the ABA signaling pathway are the protein kinase OST1 (open stomata 1) and the protein phosphatase ABI1 (ABA insensitive 1). The recently identified guard cell anion channel SLAC1 appeared to be the key ion channel in this signaling pathway but remained electrically silent when expressed heterologously. Using split YFP assays, we identified OST1 as an interaction partner of SLAC1 and ABI1. Upon coexpression of SLAC1 with OST1 in Xenopus oocytes, SLAC1-related anion currents appeared similar to those observed in guard cells. Integration of ABI1 into the SLAC1/OST1 complex, however, prevented SLAC1 activation. Our studies demonstrate that SLAC1 represents the slow, deactivating, weak voltage-dependent anion channel of guard cells controlled by phosphorylation/dephosphorylation.