Receptor-like cytoplasmic kinases facilitate RIN4-mediated plant cell-surface immunity.

Receptor-like cytoplasmic kinases facilitate RIN4-mediated plant cell-surface immunity RPM1-interacting protein 4 (RIN4) functions as a "phospho-switch" in a two-tiered plant innate immunity.The flagellin-derived peptide flg22 activates flagellin sensing 2 (FLS2)-mediated immunity and triggers phosphorylation of RIN4, which positively contributes to PAMP-triggered immunity (PTI).Subsequently, structurally unrelated Pseudomonas syringae type III effectors target and modify RIN4 to suppress cell-surface immunity, known as effector-triggered susceptibility (ETS).The post-translational modifications of RIN4 by these effectors are recognized by nucleotide-binding leucine-rich repeat receptors (NLRs), leading to effector-triggered immunity (ETI).RIN4 phosphorylation sites induced by flg22-mediated PTI are distinct from those observed in AvrB-mediated ETS induced by an Arabidopsis receptor-like cytoplasmic kinase (RLCK), RPM1-induced protein kinase (RIPK).However, the host kinase(s) for RIN4 phosphorylation during PTI activation are not addressed.Here, we demonstrate two RLCKs which trigger RIN4 phosphorylation in PTI, proposing that these RLCKs control RIN4 steadystate and phosphorylated-state, respectively, to mount full PTI responses.A bacterial type III effector targets RIN4-RLCK complexes to dampen plant cell-surface immunity and increase virulence activity.We expect that our findings will clarify how RIN4 participates in two layers of plant innate immunity by different phosphorylation events with multiple RLCKs.