Acts as a receptor for PEP defense peptides. Unlike typical immune receptors, senses an endogenous elicitor that potentiates pathogen-associated molecular pattern (PAMP)-inducible plant responses. Involved in PAMP-triggered immunity (PTI) signaling. Interacts with and phosphorylates the kinase BIK1, a central rate-limiting kinase in PTI signaling (PubMed:23431184). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with PEP1 and BAK1 (PubMed:16785433, PubMed:18824048, PubMed:20018402). Interacts with BIK1 and PBL1 (PubMed:23431184). N-glycosylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.