Acts as a calcium sensor involved in the regulatory pathway for the control of intracellular Na(+) and K(+) homeostasis and salt tolerance. Operates in synergy with CIPK24 to activate the plasma membrane Na(+)/H(+) antiporter SOS1. May function as positive regulator of salt stress responses. 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. Homodimer (By similarity). Interacts with CIPK24. Aleurone cells. Expressed in leaves. By drought stress and abscisic acid (ABA). Belongs to the calcineurin regulatory subunit family.