Plant Ca-ATPases: From biochemistry to signalling.

Calcium (Ca)-ATPases are ATP-dependent enzymes that transport Ca ions against their electrochemical gradient playing the fundamental biological function of keeping the free cytosolic Ca concentration in the submicromolar range to prevent cytotoxic effects. In plants, type IIB autoinhibited Ca-ATPases (ACAs) are localised both at the plasma membrane and at the endomembranes including endoplasmic reticulum (ER) and tonoplast and their activity is primarily regulated by Ca-dependent mechanisms. Instead, type IIA ER-type Ca-ATPases (ECAs) are present mainly at the ER and Golgi Apparatus membranes and are active at resting Ca. Whereas research in plants has historically focused on the biochemical characterization of these pumps, more recently the attention has been also addressed on the physiological roles played by the different isoforms. This review aims to highlight the main biochemical properties of both type IIB and type IIA Ca pumps and their involvement in the shaping of cellular Ca dynamics induced by different stimuli.