The plant plasma membrane H(+)-ATPase: structure, function and regulation.

The proton-pumping ATPase (H(+)-ATPase) of the plant plasma membrane generates the proton motive force across the plasma membrane that is necessary to activate most of the ion and metabolite transport. In recent years, important progress has been made concerning the identification and organization of H(+)-ATPase genes, their expression, and also the kinetics and regulation of individual H(+)-ATPase isoforms. At the gene level, it is now clear that H(+)-ATPase is encoded by a family of approximately 10 genes. Expression, monitored by in situ techniques, has revealed a specific distribution pattern for each gene; however, this seems to differ between species. In the near future, we can expect regulatory aspects of gene expression to be elucidated. Already the expression of individual plant H(+)-ATPases in yeast has shown them to have distinct enzymatic properties. It has also allowed regulatory aspects of this enzyme to be studied through random and site-directed mutagenesis, notably its carboxy-terminal region. Studies performed with both plant and yeast material have converged towards deciphering the way phosphorylation and binding of regulatory 14-3-3 proteins intervene in the modification of H(+)-ATPase activity. The production of high quantities of individual functional H(+)-ATPases in yeast constitutes an important step towards crystallization studies to derive structural information. Understanding the specific roles of H(+)-ATPase isoforms in whole plant physiology is another challenge that has been approached recently through the phenotypic analysis of the first transgenic plants in which the expression of single H(+)-ATPases has been up- or down-regulated. In conclusion, the progress made recently concerning the H(+)-ATPase family, at both the gene and protein level, has come to a point where we can now expect a more integrated investigation of the expression, function and regulation of individual H(+)-ATPases in the whole plant context.