Now that scientists have finished sequencing the human genome, they turn to a weightier matter: What gives domesticated tomatoes their tremendous girth and plumpness? New research, reported in the July 7 issue of Science, partially answers the question. Scientists at Cornell University have identified one of the more than 20 genes involved in determining the size of tomatoes. Surprisingly, the gene, called ORF-X, encodes a protein similar to one involved in human cancers. The finding suggests that the same genetic mechanism that spurs cancer growth is involved in creating plump and juicy vegetables.

Wild tomatoes are often no bigger than raspberries. Farmers have created the supersize domestic versions by crossing different varieties and selecting the offspring with the biggest tomatoes. Those plants turn out to contain mutations in nearly two dozen genes that contribute to growth--among them ORF-X. Plant biologist Steven D. Tanksley, who led the study, estimates that alterations in ORF-X can increase fruit size by 30%.

Tanksley has a theory about how the gene leads to bigger fruit. Using a powerful computer program that matches up DNA sequences to a catalog of known three-dimensional protein structures, Tanksley found that the ORF-X protein appears to fold up just like a protein that controls cell growth in humans. Based on this similarity, Tanksley believes ORF-X may play a similar role in plants.

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