Calcium-dependent protein kinase 21 phosphorylates 14-3-3 proteins in response to ABA signaling and salt stress in rice

•Yeast two-hybrid screening confirmed that OsCPK21 interacted with OsGF14e.•OsCPK21 phosphorylates OsGF14e tested by in vitro kinase assay.•Post transcriptional regulation of OsGF14e by OsCPK21 has been reported firstly.•OsCPK21 can phosphorylate tyrosine residues has been identified firstly.•OsCPK21 responses to ABA signaling and salt stress by phosphorylating OsGF14e.

The calcium-dependent protein kinases (CDPKs) are a class of plant-specific kinase that directly bind Ca2+ and mediate the calcium-signaling pathways to play important physiological roles in growth and development. The rice genome contains 31 CDPK genes, one of which, OsCPK21, is known to modulate the abscisic acid (ABA) and salt stress responses in this crop; however, the molecular mechanisms underlying this regulation are largely unknown. In the present study, we performed yeast two-hybrid screening, glutathione S-transferase pull-down, co-immunoprecipitation, and bimolecular fluorescence complementation assays to confirm the interaction between OsCPK21 and one of its putative targets, Os14-3-3 (OsGF14e). We used an in vitro kinase assay and site-directed mutagenesis to verify that OsCPK21 phosphorylates OsGF14e at Tyr-138. We used real-time PCR to reveal that several ABA and salt inducible genes were more highly expressed in the OsCPK21-OE and OsGF14e WT-OE plants than in the mutant OsGF14e Y138A-OE and wild-type plants. These results suggest that OsCPK21 phosphorylates OsGF14e to facilitate the response to ABA and salt stress.