Identification, conservation, and relative expression of V-ATPase cDNAs in tomato plants

Vacuolar H+-ATPases (V-ATPases) are multi-subunit enzymes that pump protons into intracellular compartments, thereby regulating pH levels. Because V-ATPase genes are highly conserved, using known sequences in Arabidopsis to identify orthologous acnes in other plants is possible. Using expressed sequence tags (ESTs) in the TIGR Tomato Gene Index, we have identified 23 distinct cDNAs representing all 13 known V-ATPase subunits. The subunits composing the 2-hexamer ring structures are the most highly conserved, whereas those forming peripheral stalks are the least conserved. Relative expression analyses using the same data set suggested several broad patterns of gene expression in tomato plants. V-ATPase ESTs were found in 26 of 27 libraries, normally within a 3-fold level of relative expression. EST frequencies were highest in roots, then in fruits, and essentially identical in all other tissues. In the libraries sampled, relative expression values for individual subunits varied widely and suggest that mRNAs encoding subunits a, e, and F are in low abundance in most tomato plant tissues. Finally, V-ATPase relative expression levels increased over the course of fruit ripening. The identification of cDNAs, description of conservation patterns, and preliminary expression analyses in this work should open the door for future V-ATPase studies in tomato plants.