Receptor with a serine/threonine-protein kinase activity. Involved in the perception of systemin, a peptide hormone responsible for the systemic activation of defense genes in leaves of wounded plants. May also regulate, in response to brassinosteroid binding, a signaling cascade involved in plant development (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] A 68 amino acid island between the 20th and the 21th LRR is essential for the binding of brassinosteroids. Glycosylated. SR160 is almost identical to BRI1, a brassinosteroid receptor identified in Lycopersicon esculentum. Competition experiments indicate that brassinosteroid and systemin are probably perceived by different regions of the receptor. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.