ASSESSMENT OF THE NUMBER AND EXPRESSION OF P-TYPE H+-ATPASE GENES IN TOMATO

Seven genomic fragments encoding isoforms of tomato (Lycopersicon esculentum) plasma membrane HC-ATPase were cloned and characterized. Genomic DNA gel-blot analysis indicated that probes corresponding to LHA1 through LHA7 hybridized to a common set of seven to nine restriction fragments at moderate stringency and to single, distinct fragments at high stringency. RNA gel-blot and polymerase chain reaction (PCR)-based RNA analyses indicated that LHA1, LHA2, and LHA4 transcripts were present in all organs examined (roots, hypocotyls, stems, immature leaves, mature leaves, green fruit, and red ripe fruit). LHA1 mRNA was present at similar abundance in all organs, LHA2 mRNA was most abundant in hypocotyls and leaves, and LHA4 mRNA was most abundant in roots and hypocotyls. RNA get-blot and RNA-based PCR assays indicated that LHA3, LHA5, LHA6, and LHA7 mRNA was present at very low or nondetectable levels in all organs, suggesting that these genes are either expressed at very low levels or in organs not examined or that they are regulated by hormonal or environmental cues that were not tested. Indoleacetic acid (IAA) treatment of tomato hypocotyl segments resulted in modest changes in abundance of LHA1, LHA2, and LHA4 transcripts, but these changes were not correlated with the time course of IAA-induced growth. In addition, constitutively silent LHA genes were not activated by IAA. These results indicate that at least seven genomic sequences are present in tomato that may encode plasma membrane H+-ATPases, at least three of which are expressed relatively abundantly at the mRNA level.