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. Expressed in culms and young spikelets. By salt, drought and cold stresses, and abscisic acid (ABA). Belongs to the calcineurin regulatory subunit family.