For many grocery shoppers, those perfect, red tomatoes from the store just can't match the flavor from the home garden. Now, researchers at Boyce Thompson Institute for Plant Research at Cornell University, USDA and the University of California at Davis have decoded¹ a gene² that contributes to the level of sugar, carbohydrates³（碳水化合物） and carotenoids（类胡萝卜素） in tomatoes. Cuong Nguyen, a Cornell graduate student in plant breeding working at the Boyce Thompson Institute (BTI), along with colleagues at BTI, USDA, UC Davis, Universidad Politecénica de Valencia (Spain), Universidad de Málaga (Spain) and University of Suleyman Demiral (Turkey) revealed the gene that underlies⁴ the uniform ripening⁶ mutation⁷.

This gene also influences how tomato fruits ripen⁵ and is used by commercial breeders to create tomatoes that develop into perfectly⁸ red, store-ready fruit. "Practically, it is a very important trait," says James Giovannoni, a plant molecular⁹ biologist with BTI and the U.S. Department of Agriculture, Agricultural Research Service, who is a senior author on the paper. "It's a gene that whether you realize it or not, most of your tomatoes have." However, this same trait reduces sugars and nutrients¹¹ in the fruit.

Naturally, tomatoes have uneven¹² ripening, showing darker green patches when unripe¹³ and variable redness when ripe -- traits that still show up in garden-variety and heirloom（传家宝） breeds. However, in the late 1920s, commercial breeders stumbled across a natural mutation that caused tomatoes to ripen uniformly -- from an even shade of light green to an even shade of red. This mutation, known by plant biologists as 'uniform ripening', has become indispensable to the $2 billion a year US commercial tomato market, showing up in almost all tomatoes produced for grocery stores. The uniform redness makes it ideal for the grocery sector¹⁴, which has to appeal to customer expectations of evenly colored, red fruit.

Nguyen conducted positional cloning and, with access to solgenomics.net, an online, public database hosted at BTI, he determined¹⁵ that the uniform ripening gene was located at a specific location on chromosome¹⁶ 10. With this location now known, the team could decipher the gene coding for the protein that controls photosynthesis¹⁷ levels in tomato fruit. While leaves are the primary photosynthesis factories in a plant, developing tomato fruit can contribute up to 20 percent of their own photosynthesis, yielding high sugar and nutrient¹⁰ levels in fully¹⁸ ripe fruit. The uniform ripening mutation, which commercial breeders select for, eliminates this protein in the fruit, therefore reducing sugar levels. "This is an unintended consequence," says Giovannoni, explaining why commercial growers continued to select for the trait. "Producers currently don't get a penny more for [flavor] quality."

This discovery has practical applications. Commercial producers -- who wish to produce uniform red fruit over multi-colored, flavorful ones -- can now do an early test on seedling¹⁹ DNA²⁰ for the uniform ripening mutation, rather than waiting to observe the mature fruit. Conversely, those who don't care about appearances can make sure of the opposite -- that their plants are mutation free and thus may have better-tasting fruit.