Cloning and expression of a hexose transporter gene expressed during the ripening of grape berry

The ripening of grape (Vitis vinifera L.) is characterized by massive sugar import into the berries. The events triggering this process and the pathwa ys of assimilate transport are still poorly known. A genomic clone Vvht1 (V itis vinifera hexose transporter1) and the corresponding cDNA encoding a he xose transporter whose expression is induced during berry ripening have bee n isolated. Vvht1 is expressed mainly in the berries, with a first peak of expression at anthesis, and a second peak about 5 weeks after veraison (a v ini-culture term for the inception of ripening). Vvht is strictly conserved between two grape cultivars (Pinot Noir and Ugni-Blanc). The organization of the Vvht1 genomic sequence is homologous to that of the Arabidopsis hexo se transporter, but differs strongly from that of the Chlorella kessleri he xose transporter genes. The Vvht1 promoter sequence contains several potent ial regulating cfs elements, including ethylene-, abscisic acid-, and sugar -responsive boxes. Comparison of the Vvht1 promoter with the promoter of gr ape alcohol dehydrogenase, which is expressed at the same time during ripen ing, also allowed the identification of a 15-bp consensus sequence, which s uggests a possible co-regulation of the expression of these genes. The expr ession of Vvht1 during ripening indicates that sucrose is at least partiall y cleaved before uptake into the flesh cells.