SUGAR REGULATES MESSENGER-RNA ABUNDANCE OF H-ATPASE GENE FAMILY MEMBERS IN TOMATO()

The plant plasma membrane H+-ATPase energizes the secondary uptake of nutrients and may facilitate cell expansion by acidifying the cell wal l. In yeast, Glc stimulates the accumulation of H+ ATPase mRNA, and th e growth rate supported by various sugars is correlated with H+-ATPase protein abundance. Expression of three H+-ATPase genes, LHA1, LHA2, a nd LHA4 was previously detected in tomato (Lycopersicon esculentum). W e have characterized the sequence of the LHA4 gene and examined the ex pression of these three tomato H+-ATPase genes in growing tissues and in response to exogenous sugars. LHA4 is a member of the H+-ATPase sub family, including the Arabidopsis thaliana genes AHA1, AHA2, and AHA3. The 5' untranslated region of the deduced LHA4 cDNA contains a short, open reading frame very similar to that in the Nicotiana plumbaginifo lia gene PMA1. LHA4 transcript abundance in seedlings is correlated wi th cell growth, being 2.5 times greater in hypocotyls of dark- versus light-grown plants. The accumulation of both LHA4 and LHA2 mRNAs is in duced by the addition of exogenous sugars and this induction appears t o be dependent on sugar uptake and metabolism, because mannitol and 3- O-methylglucose do not stimulate mRNA accumulation. These results sugg est that the induction of expression of H+-ATPase genes by metabolizab le sugars may be part of a generalized cellular response to increased cell growth and metabolism promoted by the availability of an abundant carbon source.