Involved in cold stress tolerance. CIPK serine-threonine protein kinases interact with CBL proteins. Binding of a CBL protein to the regulatory NAF domain of CIPK protein lead to the activation of the kinase in a calcium-dependent manner. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] May interact with CBL3. Highly expressed in leaf blade and leaf sheath, but not in other tissues. By salt, cold, calcium, sucrose and cytokinins in young seedlings, and by light in the shoot of etiolated seedlings. Induction by cold inhibited by the calcium ionophore A23187. Induction by calcium inhibited by the Ca(2+)-channel blocker La(3+), and by A23187. The activation loop within the kinase domain is the target of phosphorylation/activation by upstream protein kinases (By similarity). The N-terminal region containing the kinase domain is responsible for the autophosphorylation. Autophosphorylated. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. SNF1 subfamily.