Phosphorylation of PIP2;7 by CPK28 or Phytophthora kinase effectors dampens pattern-triggered immunity in Arabidopsis

Authors: ZHU, HAI - Nanjing Agricultural University; BAO, YAZHOU - Nanjing Agricultural University; Peng, Hao; LI, XIANGLAN - Nanjing Agricultural University; PAN, WEIYE - Nanjing Agricultural University; YANG, YUFENG - Nanjing Agricultural University; KUANG, ZIFEI - Nanjing Agricultural University; JI, PEIYUN - Nanjing Agricultural University; LIU, JINDING - Nanjing Agricultural University; SHE, DANYU - Nanjing Agricultural University; TYLER, BRETT - Oregon State University; AI, GAN - Nanjing Agricultural University; DOU, DAOLONG - Nanjing University

Submitted to: Plant Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2024
Publication Date: 9/14/2024
Citation: Zhu, H., Bao, Y., Peng, H., Li, X., Pan, W., Yang, Y., Kuang, Z., Ji, P., Liu, J., She, D., Tyler, B.M., Ai, G., Dou, D. 2024. Phosphorylation of PIP2;7 by CPK28 or Phytophthora kinase effectors dampens pattern-triggered immunity in Arabidopsis. Plant Communications. https://doi.org/10.1016/j.xplc.2024.101135.
DOI: https://doi.org/10.1016/j.xplc.2024.101135

Interpretive Summary: Plasma membrane intrinsic proteins (PIPs) are water channel proteins in the cell membrane. Upon pathogen infection, PIPs transport hydrogen peroxide from outside to the cytoplasm to enhance plant immunity. However, it is largely unknown how plants turnover PIPs to maintain their appropriate abundance. Here, we found a plant enzyme (CPK28) phosphorylate a PIP to induce its degradation. Upon pathogen infection, plants destabilize CPK28 to increase PIPs accumulation. As a counter, fungal pathogens produce conserved protein kinase effectors to reduce accumulation of this PIP. We then designed a pathogen-inducible system to express modified PIP, which can enhance plant immunity and at the same time escape degradation triggered by pathogen effectors. Our results revealed for the first time that this PIP is a plant immunity enhancer, its degradation can be induced by plant CPK28 and pathogen effectors, and the modified PIP is a good candidate for generating plants with durable resistance against fungal pathogens.

Technical Abstract: Plasma membrane intrinsic proteins (PIPs), a subclass of aquaporins (AQPs), play an important role in plant immunity by acting as H2O2 transporters upon pathogen infection. 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 from the apoplast to the cytoplasm. Arabidopsis CALCIUM-DEPENDENT PROTEIN KINASE 28 (CPK28) phosphorylates PIP2;7 at Ser273/276 to induce its subsequent degradation. During pathogen infection, plants’ rapid response to attack includes destabilization of CPK28 and dissociation of CPK28 from PIP2;7, leading to the accumulation of PIP2;7. As a counter, oomycete pathogens produce conserved kinase effectors that stably bind and phosphorylate PIP2;7 to induce its degradation. Our study supports a model by which PIP-mediated H2O2 transport is regulated in plants during infection to stimulate defense but is suppressed by conserved Phytophthora kinase effectors to promote infection. Accordingly, we developed a strategy to combat oomycete infection by using a phosphorylation-resistant PIP2;7S273/276A mutant, regulated by a pathogen-inducible synthetic upstream open reading frame (uORF). Compared to unmodified PIP2;7, PIP2;7S273/276A retains the ability to enhance plant immunity via transporting H2O2, but can escape degradation triggered by Phytophthora kinase effectors. Our novel strategy only allows accumulation of PIP2;7S273/276A during infection to limit potential side effects on normal plant growth.