ZmCRK1 negatively regulates maize's response to drought stress by phosphorylating plasma membrane H+-ATPase ZmMHA2.

Drought severely affects crop growth and yields. Stomatal regulation plays an important role in plant response to drought stress. Light-activated plasma membrane-localized proton ATPase (PM H⁺-ATPase) mainly promoted the stomatal opening. Abscisic acid (ABA) plays a dominant role in the stomatal closure during drought stress. It is not clear how PM H⁺-ATPase is involved in the regulation of ABA-induced stomatal closure. We found that a CALCIUM-DEPENDENT PROTEIN KINASE RELATED KINASE 1 (ZmCRK1), and its mutant zmcrk1 exhibited slow water loss in detached leaves, high-survival rate after drought stress, and sensitivity to stomatal closure induced by ABA. The ZmCRK1 overexpression lines are opposite. ZmCRK1 interacted with the maize PM H⁺-ATPase ZmMHA2. ZmCRK1 phosphorylated ZmMHA2 at the Ser-901 and inhibited its proton pump activity. ZmCRK1 overexpression lines and zmmha2 mutants had low H⁺-ATPase activity, resulting in impaired ABA-induced H⁺ efflux. Taken together, our study indicates that ZmCRK1 negatively regulates maize drought stress response by inhibiting the activity of ZmMHA2. Reducing the expression level of ZmCRK1 has the potential to reduce yield losses under water deficiency.