Evolution of Vacuolar Pyrophosphatases and Vacuolar H^+-Atpases in Diatoms

To cope with changing environments and maintain optimal metabolic conditions, the control of the intracellular proton gradients has to be tightly regulated. Among the important proton pumps, vacuolar H^+-ATPases (V-ATPases) and H^+-translocating pyrophosphatases (H^+-PPases) were found to be involved in a number of physiological processes, and shown to be regulated at the expression level and to exhibit specific sub-cellular localizations. Studies of the role of these transporters are relatively scarce in algae and nearly absent in diatoms. Phylogenetic analyses disclose that diatoms, with both K^+-dependent and K^+-independent membrane integral pyrophosphatases, including proteins with high homology with a novel class of Na^+,H^+-PPases. Analyses of Phaeodactylum tricornutum EST libraries show that the gene putatively encoding a Na^+,H^+-PPase is over-expressed in urea adapted condition. Genome-wide investigations of the reservoir of V-ATPases encoding subunits demonstrate that diatoms display an expended number of genes encoding for the proteolipid subunits c of the V0 subcomplex. Preliminary localization studies show that one of V0-c subunits is associated to the endoplasmic reticulum membrane in P. tricornutum. Altogether our data highlight that the combination of comparative and functional genomic approaches reach promises to provide new information to the roles of membrane proton pumps in diatoms.