Group C MAP kinases phosphorylate MBD10 to regulate ABA‐induced leaf senescence in Arabidopsis

Abstract

SUMMARYAbscisic acid (ABA) is a phytohormone that promotes leaf senescence in response to environmental stress. We previously identified methyl CpG‐binding domain 10 (MBD10) as a phosphoprotein that becomes differentially phosphorylated after ABA treatment in Arabidopsis. ABA‐induced leaf senescence was delayed in mbd10 knockout plants but accelerated in MBD10‐overexpressing plants, suggesting that MBD10 positively regulates ABA‐induced leaf senescence. ABA‐induced phosphorylation of MBD10 occurs in planta on Thr‐89, and our results demonstrated that Thr‐89 phosphorylation is essential for MBD10's function in leaf senescence. The in vivo phosphorylation of Thr‐89 in MBD10 was significantly downregulated in a quadruple mutant of group C MAPKs (mpk1/2/7/14), and group C MAPKs directly phosphorylated MBD10 in vitro. Furthermore, mpk1/2/7/14 showed a similar phenotype as seen in mbd10 for ABA‐induced leaf senescence, suggesting that group C MAPKs are the cognate kinases of MBD10 for Thr‐89. Because group C MAPKs have been reported to function downstream of SnRK2s, our results indicate that group C MAPKs and MBD10 constitute a regulatory pathway for ABA‐induced leaf senescence.