A P_(iib)-type Ca~(2+)-atpase Is Essential For Stress Adaptation In Physcomitrella Patens

摘要

Transient cytosolk Ca~(2+) ([Ca~(2+)]_(cyt)) elevations are early events in plant signaling pathways including those related to abiotic stress. The restoration of [Ca~(2+)]cyt to prestimulus levels involves ATP-driven Ca~(2+) pumps, but direct evidence for an essential role of a plant Ca~(2+)-ATPase in abiotic stress adaptation is missing. Here, we report on a stress-responsive Ca~(2+)-ATPase gene (PGA1) from the moss Physcomitrella patens. Functional analysis of PCA1 in a Ca~(2+) transport-deficient yeast mutant suggests that PCA1 encodes a P_(IIB)-type Ca~(2+)-ATPase harboring an N-terminal autoinhibitory domain. In vivo localizations identified membranes of small vacuoles as the integration site for a PCA1:GFP fusion protein. PCA1 mRNA levels are up-regulated by dehydration, NaCl, and abscisic acid, and PCA1 loss-of-function mutants (△PCA1) exhibit an enhanced susceptibility to salt stress. The △PCA1 lines show sustained elevated [Ca~(2+)]_(cyt) in response to salt treatment in contrast to WT that shows transient Ca~(2+) elevations, indicating a direct role for PCA1 in the restoration of prestimulus [Ca~(2+)]_(cyt). The altered Ca~(2+) response of the △PCA1 mutant lines correlates with altered expression levels of stress-induced genes, suggesting disturbance of a stress-associated signaling pathway. We propose that PCA1 is an essential component for abiotic stress adaptation in Physcomitrella involved in the generation of a specific salt-induced Ca~(2+) signature.