Acts as a calcium sensor. CBL proteins interact with CIPK serine-threonine protein kinases. Binding of a CBL protein to the regulatory NAF domain of a CIPK protein lead to the activation of the kinase in a calcium-dependent manner (By similarity). Homodimer (By similarity). May interact with CIPK31. Expressed in roots, shoots, culms and young spikelets. By salt and cold stresses, and abscisic acid (ABA). Belongs to the calcineurin regulatory subunit family.