Plants use cell surface-resident receptor-like kinases (RLKs) to sense diverse extrinsic and intrinsic cues and elicit distinct biological responses.Receptor activation and signal transduction are often initiated by RLK homo-and hetero-dimerization.Arabidopsis RLK BAK1 heterodimerizes with bacterial flagellin receptor FLS2 and growth hormone brassinosteroid (BR) receptor BRI1 to regulate plant immunity and development.BAK1 interacts with and directly phosphorylates receptor-like cytoplasmic kinase (RLCK) BIK1 to transduce intracellular signaling.BIK1 is rapidly phosphorylated upon bacterial flagellin perception to positively relay plant immune signaling.In contrast,BIK1 acts as a negative regulator in BR signaling via BRI1-mediated phosphorylation.It appears that distinct functions of BIK1 in plant immunity and development are regulated by the specific receptor complexes.