A Receptor-like Cytoplasmic Kinase Targeted by a Plant Pathogen Effector Is Directly Phosphorylated by the Chitin Receptor and Mediates Rice Immunity

CERK1 is a lysine motif-containing plant pattern recognition receptor for chitin and peptidoglycan. Chitin recognition by OsCERK1 triggers rapid engagement of a rice MAP kinase cascade, which leads to defense response activation. How the MAP kinase cascades are engaged downstream of OsCERK1 remains obscure. Searching for host proteins that interact with Xoo1488, an effector of the rice pathogen Xanthomonas oryzae, we identified the rice receptor-like cytoplasmic kinase, OsRLCK185. Silencing OsRLCK185 suppressed peptidoglycan- and chitin-induced immune responses, including MAP kinase activation and defense-gene expression. In response to chitin, OsRLCK185 associates with, and is directly phosphorylated by, OsCERK1 at the plasma membrane. Xoo1488 inhibits peptidoglycan- and chitin-induced immunity and pathogen resistance. Additionally, OsCERK1-mediated phosphorylation of OsRLCK185 is suppressed by Xoo1488, resulting in the inhibition of chitin-induced MAP kinase activation. These data support a role for OsRLCK185 as an essential immediate downstream signaling partner of OsCERK1 in mediating chitin- and peptidoglycan-induced plant immunity. ► Xanthomonas effector Xoo1488 interacts with the cytoplasmic receptor-like kinase OsRLCK185 ► The rice chitin receptor CERK1 directly interacts with and phosphorylates OsRLCK185 ► OsRLCK185 transmits immune signals from CERK1 to the downstream MAPK components ► OsRLCK185 phosphorylation is inhibited by Xoo1488 to impair pathogen resistance