ANCIENT ORIGIN OF THE VACUOLAR H-ATPASE 69-KILODALTON CATALYTIC SUBUNIT SUPERFAMILY()

Recently, two distinct cDNA clones encoding the catalytic subunit of t he vacuolar H+-ATPase (V-ATPase) were isolated from the allotetraploid cotton species Gossypium hirsutum L. cv 'Acala SJ-2' (Wilkins 1992, 1 993). Differences in the nucleotide sequence of these clones were used as molecular markers to explore the organization and structure of the V-ATPase catalytic subunit genes in the A and D genomes of diploid an d allotetraploid cotton species. Nucleotide sequencing of polymerase c hain reaction (PCR) products amplified from G. arboreum (A(2), 2n=26), G. raimondii (D-5, 2n=26), and G. hirsutum cv 'Acala SJ-2' [(AD)(1), 2n=4x=52] revealed a V-ATPase catalytic subunit organization more comp lex than indicated hitherto in any species, including higher plants. I n the genus Gossypium, the V-ATPase catalytic subunit genes are organi zed as a superfamily comprising two diverse but closely related multig ene families, designated as vat69A and vat69B, present in both diploid and allotetraploid species. As expected, each vat69 subfamily is corr espondingly more complex in the allotetraploid species due to the pres ence of both A and D alloalleles. Because of this, about one-half of t he complex organization of V-ATPase catalytic subunit genes predates p olyploidization and speciation of New World tetraploid species. Compar ison of plant and fungal V-ATPase catalytic subunit gene structure ind icates that introns accrued in the plant homologs following the bifurc ation of plant and fungi but prior to the gene duplication event that gave rise to the vat69A and vat69B genes approximately 45 million year s ago. The structural complexity of plant V-ATPase catalytic subunit g enes is highly conserved, indicating the presence of at least ten intr ons dispersed throughout the coding region.