Scientists Discover Link Between Tomato Ripening, Color, Taste

DAVIS, Calif.Its hard to find that oh-so perfect red tomato packed with flavor; however, that all might change now that researchers have decoded a gene that contributes to the level of sugar, carbohydrates and carotenoids in tomatoes, according to a new study published in the journal Science. The findings have significant implications for the $2 billion U.S. tomato industry, which annually harvests more than 15 million tons of the fruit for processing and fresh-market sales.

Researchers at Boyce Thompson Institute for Plant Research (BTI) at Cornell University, USDA and the University of California at Davis revealed the gene that underlies the uniform ripening mutation. This gene also influences how tomato fruits ripen and is used by commercial breeders to create tomatoes that develop into perfectly red, store-ready fruit.

This information about the gene responsible for the trait in wild and traditional varieties provides a strategy to recapture quality characteristics that had been unknowingly bred out of modern cultivated tomatoes," said Ann Powell, a biochemist in UC Davis Department of Plant Sciences and one of the lead authors of the study. Now that we know that some of the qualities that people value in heirloom tomatoes can be made available in other types of tomatoes, farmers can have access to more varieties of tomatoes that produce well and also have desirable color and flavor traits," she said.

For decades, plant breeders in the tomato industry have selected varieties that are uniformly light green before they ripen, in order to produce tomatoes that can be harvested at the same time. However, this characteristic is accompanied by an unintended reduction in sugars that compromises the flavor of the fresh fruit and its desirability for processing.

The UC Davis researchers began studying the genes influencing tomato fruit development and ripening after spending two summers screening tomato plants for transcription factors that might play a role in both fruit color and quality. Transcription factors are proteins that regulate genes, or turn them on and off. These factors themselves are manufactured or expressed by genes. They were particularly interested in tomatoes they observed in the field that were unusually dark green before they ripened.

Partnering with researchers at Cornell University and in Spain, who were mapping regions of the tomato genome, the scientists discovered two transcription factors, called GLK1 and GLK2, that control the development of chloroplasts. Chloroplasts are the structures in the plant cells that enable plants to photosynthesize, converting the energy of sunlight into sugars and other compounds that influence flavor and color.

The researchers scoured a collection of mutant and wild species of tomatoes at UC Davis established at UC Davis by the late Professor Charles Rick beginning in the 1950s. They discovered that dark green tomatoes that naturally express GLK2 produced ripe fruit with increased levels of sugars or soluble solids, important for processing tomatoes, as well as higher levels of the health-promoting compound lycopene.