Contributes to pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) signaling, including calcium signaling and root growth inhibition, and defense responses downstream of FLS2 (PubMed:20413097, PubMed:25522736). Acts additively with BIK1 in PTI defenses (PubMed:20413097, PubMed:25522736). Seems not required for flg22-induced MAPK activation (Probable). Required for Pep1-induced defenses (PubMed:25522736). Pep1 is an endogenous elicitor that potentiates PAMP-inducible plant responses (PubMed:23431184, PubMed:25522736). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with FLS2 (PubMed:20413097). Interacts with PEPR1 (PubMed:23431184). Myristoylation and proper targeting to plasma membrane is essential for signaling function in response to pathogen-associated molecular pattern (PAMP) such as flg22. A number of isoforms are produced. According to EST sequences. Induced by flagellin (flg22). Phosphorylated upon flagellin (flg22) treatment. No visible phenotype under normal growth conditions (PubMed:20413097). Abrogated kinase activity (PubMed:25522736). In cce5-2 and cce5-4, reduced calcium levels after elicitation with peptides representing bacteria-derived microbe- and damage-associated molecular patterns (MAMPs, flg22 and elf18, and the endogenous DAMP AtPep1), but normal response to chitin octamers. Reduced root growth inhibition response to flg22 (PubMed:25522736). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.