Receptor-like cytoplasmic kinase involved in the transduction of signal between the host cell surface chitin receptor complex CERK1-LYK5 and the intracellular MAPKKK5-dependent mitogen-activated protein kinase (MAPK) cascade that leads to chitin-induced immunity (PubMed:24750441, PubMed:27679653). Phosphorylates and activates MAPKKK5 when phosphorylated by CERK1 after elicitation by chitin (PubMed:27679653). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with CERK1 (preferentially unphosphorylated) at the plasma membrane (PubMed:24750441, PubMed:27679653). Binds to MAPKKK5 at the plasma membrane; disassociation is induced by chitin perception by the CERK1 complex. Associates also with MAPKKK3 (PubMed:27679653). Levels are regulated in a proteasome-dependent manner (at proteome level). Phosphorylated by CERK1 upon elicitation by chitin. Palmitoylation at Cys-4 and Cys-7 are required for plasma membrane location. Impaired chitin-induced defense responses such as MAPK activation (e.g. MPK3/6) and callose deposition leading to reduced disease resistance against fungal (e.g. A.brassicicola) and bacterial (e.g. P.syringae pv. tomato DC3000 hrcC) infections. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Extended C-terminus.