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. Acts as a negative regulator of the plasma membrane proton pump AHA2 by preventing its interaction with 14-3-3 protein. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with CBL1, CBL2, CBL3, CBL4/SOS3, and CBL5. Expressed in roots and stems, but barely detectable in flowers and siliques. Expressed in hypocotyls and roots upon germination. As seedlings mature, detected in the vascular tissue of both the stem and leaf. Up-regulated by salt, drought, abscisic acid and glucose, but not by cold. The activation loop within the kinase domain is the target of phosphorylation/activation by upstream protein kinases. The PPI motif mediates the interaction with the ABI (abscisic acid-insensitive) phosphatases (By similarity). Autophosphorylated. Increased proton extrusion and resistance to high external pH. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. SNF1 subfamily.