The rice SCFOsFBK1 E3 ligase mediates jasmonic acid induced degradation of a RING-H2 protein and the cinnamoyl-CoA reductase, OsCCR14

Abstract 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.