Acts as a receptor for PEP defense peptides. Unlike typical immune receptors, senses an endogenous elicitor that potentiates PAMP-inducible plant responses (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with BAK1 (PubMed:20018402). Interacts with CLE14 (PubMed:28586647). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.