May play a role in signal transduction of hyperosmotic response. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phosphorylation (By similarity). Activated by hyperosmotic stress. Expressed in leaf blades, leaf sheaths and roots of plants grown hydroponically. Expressed in shoots and roots of young seedlings. Expressed in leaves and maturing seeds, but not in roots and stems of field-grown plants. By abscisic acid (ABA) in leaf blades and leaf sheaths (PubMed:15084714). Induced during incompatible interaction with the bacterial pathogen Xanthomonas oryzae pv. oryzicola (Ref.3). Autophosphorylated in presence of Ca(2+). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.