Expression of three expansin genes during development and maturation of Kyoho grape berries.

Expansins are cell-wall-localized proteins that induce loosening of isolated plant cell walls in vitro in a pH-dependent manner, but exhibit no detectable hydrolase or transglycosylase activity. Three putative expansin cDNAs, Vlexp1, Vlexp2, and Vlexp3 were isolated from a cDNA library made from mature berries of the Kyoho grape. Expression profiles of the 3 genes were analyzed throughout berry development. Accumulation of the Vlexp3 transcript was closely correlated with berry softening, and expression of this gene was detected before véraison and markedly increased at véraison (onset of berry softening). Expression of Vlexp3 was berry-specific. Vlexp1 and Vlexp2 mRNA accumulation began during the expansion stage of berry development and expression increased for both genes during ripening. Vlexp1 and Vlexp2 mRNA was detected in leaf, tendril and flower tissues and Vlexp2 mRNA was additionally detected in root and seed tissues. These findings suggest that the three expansin genes are associated with cell division or expansion and berry ripening. Vlexp3, in particular, is most likely to play a role in grape berry softening at véraison.