Involved in drought 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] Expressed at low levels in leaf blades. By drought stress and abscisic acid (ABA). 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. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. SNF1 subfamily.