Leucine-rich repeat receptor protein kinase that acts as sensor of extracellular hydrogen peroxide (PubMed:32076270). Required for intracellular calcium influx in response to extracellular hydrogen peroxide (PubMed:32076270). Mediates hydrogen peroxide-induced activation of calcium channels in guard cells and is required for stomatal closure (PubMed:32076270). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by autophosphorylation on serine and threonine residues in response to extracellular hydrogen peroxide. Widely expressed. Autophosphorylated at Ser-606, Ser-607, Thr-786, Thr-789, Thr-790 and Ser-942 in response to extracellular hydrogen peroxide. No visible phenotype under normal growth conditions, but mutant seedlings exhibit reduced accumulation of intracellular calcium in response to extracellular hydrogen peroxide. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.