Alteration of fruit characteristics in transgenic tomatoes with modified expression of a xyloglucan endotransglucosylase/hydrolase gene

Some cell wall enzymes of the xyloglucan endotransglucosylase/hydrolase (XTH) family catalyze molecular grafting between xyloglucan molecules. In tomato, 25 genes for XTH proteins have been identified. We studied the tomato gene SlXTH1, which has highest homology to the cDNA of the XTH first purified from hypocotyls of Vigna angularis. SlXTH1 mRNA was found to accumulate transiently at an early stage of fruit development, and the peak day of accumulation was about 12 days after pollination. The expression profile of SlXTH1 mRNA was roughly associated with that of the reported enzyme activity, suggesting that the SlXTH1 protein may be one of the main determinants of the enzyme activity. We then examined how alteration of expression of the SlXTH1 gene could influence the characteristics of fruits. Several lines of transgenic tomatoes with different levels of SlXTH1 transcript were produced by introducing a SlXTH1 transgene in either the sense or antisense orientation downstream of a constitutive promoter. In these transgenic tomatoes, fruit size was positively correlated with the level of SlXTH1 transcript, which was monitored at its peak stage. This is the first in vivo demonstration that SlXTH1 can control the morphological character of plants through changes in its level of expression.