RESUMEN

Plasma membrane intrinsic proteins (PIPs), a subclass of aquaporins (AQPs), play an important role in plant immunity by acting as H2O2 transporters. Their homeostasis is mostly maintained by C-terminal serine phosphorylation. However, the kinases that phosphorylate PIPs and manipulate their turnover are largely unknown. Here, we found that Arabidopsis thaliana PIP2;7 positively regulates plant immunity by transporting H2O2. Arabidopsis CALCIUM-DEPENDENT PROTEIN KINASE 28 (CPK28) directly interacts with and phosphorylates PIP2;7 at Ser273/276 to induce its degradation. During pathogen infection, CPK28 dissociated from PIP2;7 and destabilized, leading to PIP2;7 accumulation. As a counter, oomycete pathogens produce the conserved kinase effectors that stably bind and mediate the phosphorylate of PIP2;7 to induce its degradation. Our study identifies PIP2;7 as a novel substrate of CPK28 and its protein stability is negatively regulated by CPK28. Such phosphorylation could be mimicked by Phytophthora kinase effectors to promote infection. Accordingly, we developed a strategy to combat oomycete infection by using a phosphorylation-resistant PIP2;7S273/276A mutant. The strategy only allows accumulation of PIP2;7S273/276A during infection to limit potential side effects on normal plant growth.