Acts as a calcium sensor involved in abscisic acid (ABA) signaling and stress-induced ABA biosynthesis pathways. Contributes to the regulation of early stress-related CBF/DREB transcription factors. 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. May function as a negative regulator of stress and ABA responses. Mediates the activation of AKT1 by CIPK proteins (CIPK6, CIPK16, and CIPK23) in response to low potassium conditions and in the context of stomatal movement. Involved in the calcium-dependent regulation by CIPK26 of reactive oxygen species production by the NADPH oxidase RBOHF. The CBL9/CIPK3 complex acts in the regulation of abscisic acid response in seed germination. Homodimer (By similarity). Part of a K(+)-channel calcium-sensing kinase/phosphatase complex composed by a calcium sensor CBL (CBL1, CBL2, CBL3 or CBL9), a kinase CIPK (CIPK6, CIPK16 or CIPK23), a phosphatase PP2C (AIP1) and a K(+)-channel (AKT1). Interacts with CIPK1, CIPK3, CIPK6, CIPK8, CIPK14, CIPK16, CIPK18, CIPK21, CIPK23, CIPK24 and CIPK26. Plasma membrane localization abolished by 2-bromopalmitate (2-BP) treatment. Ubiquitous. Colocalized with CIPK23 in root tips and vascular bundles in the stem and the leaf, as well as in guard cells and root hairs. By drought, cold, salt and abscisic acid (ABA) treatments. The N-terminal 12 amino acids are sufficient for cell membrane targeting. Both N-myristoylation and calcium-mediated conformational changes are essential for its function. Hypersensitivity to abscisic acid in the early developmental stages. Belongs to the calcineurin regulatory subunit family.