Probable receptor. Interaction with a ligand in the extracellular domain triggers the protein kinase activity of the cytoplasmic domain. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Expressed predominantly in the shoots and roots of young maize seedlings, and to a lesser extent in the silks. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.