May play a role in signal transduction pathways that involve calcium as a second messenger. Functions as regulator of the calcium-mediated abscisic acid (ABA) signaling pathway. Phosphorylates ABA-responsive transcription factors ABF1 and ABF4 in vitro. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by calcium. Autophosphorylation may play an important role in the regulation of the kinase activity (By similarity). Interacts with Di19. By drought and high-slat stress, but not by low-temperature, heat stress or abscisic acid treatment. There are 3 contiguous domains conserved in the CDPK subfamily: a kinase domain, an autoinhibitory (junction) domain and a calmodulin-like domain. The autoinhibitory domain (290-320) inactivates kinase activity under calcium-free conditions (By similarity). Mutant cpk11-2 shows reduced ABA and salt responsiveness in seed germination. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDPK subfamily.