Ca2+ signatures: the role of Ca2+-ATPases.

Calcium ions (Ca) are well known signaling molecules in plant signal transduction pathways including the response to abiotic stress. Particular stimuli cause specific transient elevations in cytosolic Ca ([Ca]) with a stimulus-dependent amplitude and temporal pattern. These Ca transients, known as Ca signatures, rely on the counteractive activities of Ca-permeable channels and Ca-transporting proteins. Whereas the channels causing an increase in [Ca] were partly identified, direct evidence for the role of Ca-transporting proteins in the determination of Ca signatures was missing. We recently reported on the functional characterization of a stress-responsive P-type Ca-ATPase (PCA1) from the moss . This study revealed an essential role of this Ca pump in the adjustment of salt stress tolerance. Most strikingly, the generation of a specific Ca signature in response to salt was abolished in Physcomitrella mutant lines lacking PCA1 activity. Thus, we can provide a direct link for the function of a Ca-ATPase in the generation of a specific Ca signature in plants.