Involved in the regulatory pathway for the control of intracellular Na(+) and K(+) homeostasis and salt tolerance. Activates the vacuolar H(+)/Ca(2+) antiporter CAX1 and operates in synergy with CBL4/SOS3 to activate the plasma membrane Na(+)/H(+) antiporter SOS1. 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. Phosphorylates CBL1, CBL4 and CBL10. 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, CBL4/SOS3, CBL5, CBL9, CBL10 and with the protein phosphatase 2C ABI2. Targeted to the cell membrane when interacting with CBL1 or CBL5 and to the tonoplast when interacting with CBL2 orCBL10. Up-regulated in roots by salt stress. 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. The C-terminal part (309-446) of the protein is required for the phosphorylation of CBL, but is not involved in autophosphorylation. Autophosphorylated. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. SNF1 subfamily.