S-domain receptor protein kinase involved in lipopolysaccharide (LPS) sensing (PubMed:25729922, PubMed:29431629, PubMed:31922267). Specifically detects LPS of Pseudomonas and Xanthomonas species (PubMed:25729922). LPS are major components of the outer membrane of Gram-negative bacteria and are important microbe-associated molecular patterns (MAMPs) that trigger biphasic production of reactive oxygen species (ROS) and immune responses in plants (PubMed:25729922, PubMed:29431629). Seems to be only partially associated with the second LPS-triggered ROS burst (PubMed:29431629). Mediates defense signaling in response to the medium-chain 3-hydroxy fatty acid 3-OH-C10:0, a pathogen-associated molecular pattern (PAMP) which induces autophosphorylation at Tyr-600 (PubMed:31922267). Autophosphorylation at Tyr-600 is required for downstream phosphorylation of the receptor-like cytoplasmic kinase PBL34, PBL35 and PBL36, and activation of plant immunity (PubMed:31922267). (Microbial infection) Targeted by the bacterial type III effector protein tyrosine phosphatase HopAO1 from Pseudomonas syringae (PubMed:31922267). HopAO1 dephosphorylates Tyr-600, which suppresses the immune response (PubMed:31922267). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Interacts with PUB9, PUB13, PUB14, PUB29, PUB38, PUB44 and PUB45 (PubMed:18552232). Interacts with PBL34, PBL35 and PBL36 (PubMed:31922267). Repressed by miR393a (microRNA) in response to bacterial lipopolysaccharides (LPS) treatment. Autophosphorylated at Tyr-600 (PubMed:31922267). Autophosphorylation at Tyr-600 is required for downstream phosphorylation of the receptor-like cytoplasmic kinase PBL34, PBL35 and PBL36, and activation of plant immunity (PubMed:31922267). No visible phenotype under normal growth conditions, but mutant plants are hyper-susceptible to infection by the bacterial pathogen Pseudomonas syringae. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.