A Plant Lectin Receptor-like Kinase Phosphorylates the Bacterial Effector AvrPtoB to Dampen Its Virulence in Arabidopsis

Plasma membrane-localized receptor-like kinases(RLKs)perceive conserved pathogen-associated molecular pattems(PAMPs)in plants,leading to PAMP-triggered immunity(PTI).TheArabidopsis thaliana lectin RLK LecRK-Ⅸ.2 has been shown to regulate the bacterial flagellin-derived peptide flg22-induced PTI.Here,we discover that Pseudomonas syringae effector AvrPtoB targets LecRK-Ⅸ.2 for degradation,which subsequently suppresses LecRK-Ⅸ.2-mediated PTI and disease resistance.However,LecRK-Ⅸ.2 can interact with and phosphorylate AvrPtoB at serine site 335(S335).AvrPtoB self-associates in vitro and in vivo,and the association appears to be essential for its E3 ligase activity in ubiquitinating substrate in plants.Phosphorylation of S335 disrupts the self-association and as a result,phosphomimetic AvrPtoBS335D cannot ubiquitinate LecRK-Ⅸ.2 efficiently,leading to the compromised virulence of AvrPtoB in suppressing PTI responses.fig22 enhances AvrPtoB S335 phosphorylation by inducing the expression and activating of LecRK-Ⅸ.2.Our study demonstrates that host RLKs can modify pathogen effectors to dampen their virulence and undermine their ability in suppressing PTI.