May play a role in signal transduction pathways that involve calcium as a second messenger (By similarity). Serine/threonine kinase that phosphorylates histone H3 an GLN1-1. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Not activated by calcium. Autophosphorylation may play an important role in the regulation of the kinase activity. Stimulated by magnesium ions (optimum at 10-15 mM) and manganese ions. Optimum pH is 8. Binds calmodulin (CaM) in a calcium-dependent manner. Interacts with GLN1-1. Ubiquitously expressed with higher levels in siliques and roots, especially at the root cap. Particularly present in vascular bundles of stems and leaves. During flower development, abundantly present in the apical meristem. During pollen development, there are high levels in pollen mother cells and it accumulates gradually to reach a peak during the tetrad stage. Fades out in mature pollen. Also present in tapetal cells and at stigmatic surface of the stigma. By abscisic acid (ABA) and during leaf senescence. 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 (409-439) inactivates kinase activity under calcium-free conditions (By similarity). Autophosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDPK subfamily.