ZmCPK11 is involved in abscisic acid-induced antioxidant defence and functions upstream of ZmMPK5 in abscisic acid signalling in maize

Calcium-dependent protein kinases (CDPKs) have been shown to be involved in abscisic acid (ABA)-mediated physiological processes, including seed germination, post-germination growth, stomatal movement, and plant stress tolerance. However, it is not clear whether CDPKs are involved in ABA-induced antioxidant defence. In the present study, the role of the maize CDPK ZmCPK11 in ABA-induced antioxidant defence and the relationship between ZmCPK11 and ZmMPK5, a maize ABA-activated mitogen-activated protein kinase (MAPK), in ABA signalling were investigated. Treatments with ABA and H2O2 induced the expression of ZmCPK11 and increased the activity of ZmCPK11, while H2O2 was required for the ABA-induced increases in the expression and the activity of ZmCPK11. The transient gene expression analysis and the transient RNA interference (RNAi) test in protoplasts showed that ZmCPK11 is involved in ABA-induced up-regulation of the expression and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), and in the production of H2O2. Further, ZmCPK11 was shown to be required for the up-regulation of the expression and the activity of ZmMPK5 in ABA signalling, but ZmMPK5 had very little effect on the ABA-induced up-regulation of the expression and the activity of ZmCPK11. Moreover, the transient gene expression analysis in combination with the transient RNAi test in protoplasts showed that ZmCPK11 acts upstream of ZmMPK5 to regulate the activities of antioxidant enzymes. These results indicate that ZmCPK11 is involved in ABA-induced antioxidant defence and functions upstream of ZmMPK5 in ABA signalling in maize.