Lysin motif (LysM) receptor kinase that functions as a cell surface receptor in chitin elicitor (chitooligosaccharides) signaling leading to innate immunity toward both biotic and abiotic stresses (e.g. tolerance to salinity, heavy-metal stresses, and Botrytis cinerea infection). Recognizes microbe-derived N-acetylglucosamine (NAG)-containing ligands. Involved in the resistance to pathogenic fungi Alternaria brassicicola and Erysiphe cichoracearum, probably by sensing microbe-associated molecular patterns (MAMP) and pathogen-associated molecular patterns (PAMP). Plays an essential role in detecting peptidoglycans (e.g. PGNs) and restricting bacterial growth. Target of the bacterial type III effector E3-ligase protein hopAB2/avrPtoB of Pseudomonas syringae pv. tomato DC3000 that mediates ubiquitination and subsequent proteolysis, thus blocking all defense responses by suppressing PAMP-triggered immunity (PTI). Mediates chitin-induced phosphorylation of PBL27 (PubMed:24750441). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by chitin-mediated homodimerization. Forms homodimers and homooligomers. Homodimerization is required to trigger plant defenses. Binds to chitin, chitosan and chito-oligomer oligosaccharide elicitors. Interaction with chitin octamer (NAG(8)) promotes homodimerization while shorter chitin oligomers inhibit homodimerization. Interacts with Pseudomonas syringae hopAB2/avrPtoB. Interacts (preferentially when unphosphorylated) with PBL27 at the plasma membrane (PubMed:24750441, PubMed:27679653). Binds to IOS1 (PubMed:27317676). Expressed ubiquitously, with lowest expression in pollen. Induced upon treatment with chitin oligosaccharide elicitor and flagellin (e.g. flg22). Autophosphorylated. Autophosphorylation is induced by chitin and derivatives. Ubiquitinated and targeted to the proteasome by hopAB2/avrPtoB of Pseudomonas syringae pv. tomato DC3000. Complete loss of response to the chitin elicitor, including loss of MAPK activation, generation of reactive oxygen species, and transcriptional activation. Impaired chitin-mediated resistance against biotic and abiotic stresses such as tolerance to salinity, heavy-metal stresses, and Botrytis cinerea infection. Reduced resistance to incompatible fungi such as Erysiphe cichoracearum and Alternaria brassicicola. Enhanced susceptibility to Pseudomonas syringae pv. tomato DC3000 associated with peptidoglycan insensitivity. Impaired chitin-induced phosphorylation of PBL27 (PubMed:24750441). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.