Plant responses to multiple environmental stresses include various signaling pathways that allow plant acclimation and survival. Amongst different stresses, drought and heat stress severely affect growth and productivity of wheat. HVA1, a member of the group 3 LEA protein, has been well known to provide protection against drought stress. However, its mechanism of action and its role in other stresses such as heat remain unexplored. In this study, doubled haploid (DH) wheat plants overexpressing the HVA1 gene were analyzed and found to be both drought-and heat stress-tolerant. The transcriptome analysis revealed the upregulation of transcription factors such as DREB and HsfA6 under drought and heat stress, respectively, which contribute toward the tolerance mechanism. Particularly under heat stress conditions, the transgenic plants had a lower oxidative load and showed enhanced yield. The overexpression lines were found to be ABA-sensitive, therefore suggesting the role of HsfA6 in providing heat tolerance via the ABA-mediated pathway. Thus, apart from its known involvement in drought stress, this study highlights the potential role of HVA1 in the heat stress signaling pathway. This can further facilitate the engineering of multiple stress tolerance in crop plants, such as wheat.
We have shown earlier the F-box protein, OsFBK1, mediating turn-over of a cinnamoyl CoA-reductase, OsCCR14, to regulate rice anther and root lignification. Currently, we have identified OsATL53, a member of ATL family of RING-H2 proteins interacting with OsCCR14 in cytoplasm. OsATL53 was identified in the same Y2H library screening as reported before for OsCCR14. OsATL53 has been found to have a cytoplasmic localization and has E3 ligase ubiquitination properties. SCF OsFBK1 mediates turn-over of OsATL53 in cytoplasm and nucleus, while of OsCCR14 in the nucleus as validated by cell-free degradation assays. In presence of jasmonic acid (JA), which plays a role in anther dehiscence, confocal FLIM analyses demonstrate OsATL53-OsCCR14 undergoing conformational changes that trigger the complex to accumulate around the nuclear periphery and signals OsFBK1 to initiate degradation of the proteins in respective cellular compartments. Biochemically, OsATL53 decreases enzymatic activity of OsCCR14 and sequesters it in the cytoplasm thereby regulating the lignification process. Knock-down rice transgenics of OsATL53 display increased lignin deposition in the anthers and roots vis-a-vis wild-type, while those of OsCCR14 have decreased lignin content. These data show OsATL53 affects activity of OsCCR14, and their JA induced degradation by SCF OsFBK1 regulates lignification of rice anthers and roots.
We had previously shown the rice F-box, OsFBK1, plays a role in anther development by mediating the turnover of OsCCR14, a cinnamoyl CoA-reductase regulating lignification. Another substrate identified in the same Y2H library screening was OsATL53, a member of the ATL family of RING-H2 proteins that is primarily localized to the cytoplasm. We found OsATL53 to be a component and substrate of SCFOsFBK1 by immunoprecipitation and cell-free studies. Incidentally, OsATL53 was found to interact with OsCCR14 in the cytoplasm and form a stable complex in cell-free experiments and bimolecular fluorescence complementation assays. Biochemically, OsATL53 was found to influence the enzymatic activity of OsCCR14 by decreasing its efficiency. Degradation studies have shown OsFBK1 mediates turnover of OsCCR14 in the nucleus, while OsATL53 is degraded in both cytoplasm and nucleus. The degradation of ATLs by F-box proteins has not been reported before. In presence of jasmonic acid (JA), which plays a role in anther dehiscence, OsATL53 has been found to gather around the nucleus, and this property enables the translocation of the OsATL53-OsCCR14 complex from a cytoplasmic localization to accumulate around the nuclear periphery. FLIM analyses revealed OsCCR14-OsATL53 complex undergoing conformational changes in presence of JA and this triggers OsFBK1 to mediate the targeted degradation of OsATL53 in the cytoplasm, thereby dissociating the cytoplasmic OsCCR14-OsATL53 complex and enabling OsCCR14 to enter the nucleus and eventually get degraded by SCFOsFBK1 E3 ligase. We have thus studied the signalling mechanism of a variant JA-induced E3 ligase-mediated substrate turnover in plants at the molecular level.
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