May play a role in signal transduction pathways that involve calcium as a second messenger (Probable). Acts as developmentally controlled regulator for coordinated stem elongation and vascular development. Acts as key component which contributes to the developmental switch that establishes the transition from vegetative to reproductive growth (PubMed:23252373). Involved in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) signaling. Interacts with and phosphorylates the kinase BIK1, a central rate-limiting kinase in PTI signaling. Facilitates BIK1 turnover and negatively regulates BIK1-mediated immune responses triggered by several PAMPs. Its kinase activity is necessary and sufficient for its function in PTI signaling (PubMed:25525792). 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 (PubMed:23252373). Autophosphorylation plays an important role in the regulation of the kinase activity (PubMed:23252373). Interacts with BIK1. Expressed in vascular and meristematic tissues throughout plant development. 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 (328-358) inactivates kinase activity under calcium-free conditions (By similarity). Severe growth defect in shoot elongation. Severe growth defect of flowering stem. May be due to an intron retention. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDPK subfamily.