Previous research has shown that the sugar sucrose plays a role in controlling key fruit genes involved in sugar metabolism. Efforts to control these genes succeeded in increasing the sugar content in fruit but also resulted in stunted growth.
Researchers from Tohoku University in Japan used a bioinformatics search tool to find nucleotide sequences in the tomato genome similar to a known tobacco gene sequence that can be repressed by sucrose. When a special coding sequence on the tobacco gene, called a uORF, is removed and the main sequence is made to overexpress, the gene activates several other genes involved in sugar metabolism, ultimately increasing sucrose levels in tobacco leaves. When the uORF is not removed, an overexpressing gene will increase sucrose content in the tobacco leaves but only up to a point. The increased sucrose represses the uORF, which in turn represses the main part of the gene, limiting its ability to further increase the fruit's sucrose content.
Two genes with very similar sequences to the tobacco gene were identified in the tomato plant by the researchers' bioinformatics search and their uORFs were removed.