ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with TOPP1. A number of isoforms are produced. According to EST sequences. Expressed in seedlings. By abscisic acid (ABA), salt, and osmotic stress (at protein level). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.