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

Seven genomic fragments encoding isoforms of tomato (Lycopersicon escu lentum) plasma membrane HC-ATPase were cloned and characterized. Genom ic DNA gel-blot analysis indicated that probes corresponding to LHA1 t hrough LHA7 hybridized to a common set of seven to nine restriction fr agments at moderate stringency and to single, distinct fragments at hi gh stringency. RNA gel-blot and polymerase chain reaction (PCR)-based RNA analyses indicated that LHA1, LHA2, and LHA4 transcripts were pres ent in all organs examined (roots, hypocotyls, stems, immature leaves, mature leaves, green fruit, and red ripe fruit). LHA1 mRNA was presen t at similar abundance in all organs, LHA2 mRNA was most abundant in h ypocotyls and leaves, and LHA4 mRNA was most abundant in roots and hyp ocotyls. RNA get-blot and RNA-based PCR assays indicated that LHA3, LH A5, LHA6, and LHA7 mRNA was present at very low or nondetectable level s in all organs, suggesting that these genes are either expressed at v ery low levels or in organs not examined or that they are regulated by hormonal or environmental cues that were not tested. Indoleacetic aci d (IAA) treatment of tomato hypocotyl segments resulted in modest chan ges in abundance of LHA1, LHA2, and LHA4 transcripts, but these change s were not correlated with the time course of IAA-induced growth. In a ddition, constitutively silent LHA genes were not activated by IAA. Th ese 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.