Abstract
Like all other eukaryotes, plants utilize calcium as an important secondary messenger for signal transduction. Among plants, calcium signals are particularly important for triggering physiological responses to environmental perturbations or stresses. Calcineurin B-Like proteins (CBLs) are prominent examples of plant calcium-sensor proteins involved in environmental responses. CBLs regulate the activities of a family of SNF1-related kinases, known as CBL-interacting protein kinases (CIPKs), in a calcium-dependent manner. The CBL–CIPK network appears to be present in all land plants and certain green algae, though its functions have only been studied in higher plants. Among higher plants, the network typically consists of about 10 CBLs and 25–30 CIPKs. Through combinatorial interactions among these proteins, the CBL–CIPK network enables integration of multiple signals of the plant’s environment and coordinates downstream responses to stresses such as nutrient deprivation or toxic ion exposure. The CBL–CIPK network thus represents a major decoding mechanism for various calcium signatures in response to extracellular cues.