Probable receptor-like serine/threonine-protein kinase involved in abscisic acid (ABA) signaling. Acts as a positive regulator of abiotic stress response. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] A number of isoforms are produced by alternative splicing of isoform 1. ABA-insensitive and drought stress-semsitive. Late flowering. Produced by alternative promoter usage. Produced by alternative splicing of isoform 2. May be due to an intron retention. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. The predicted gene has been split into 2 genes: At1g18390 and At1g18400. Cloning artifact.