Tomato genome sequenced

There are over 7000 varieties of cultivated tomatoes, but there is little genetic variation between them. Image: Robert Kneschke/Shutterstock

Breeding for appearance may lead to a sacrifice in flavour.

An international team of scientists has succeeded in decoding the tomato (Solanum lycopersicum). The sequence provides all the genes of the organism and will be the ultimate tool for breeders, who can use it to design markers to accelerate or assist breeding activities.

“For any characteristic of the tomato, whether it’s taste, natural pest resistance or nutritional content, we’ve captured virtually all those genes,” says Cornell University researcher James Giovannoni, who led the US sequencing team. “The sequence will make breeding for flavour, yield, colour, shelf-life or any trait of interest more efficient.”

The genome was sequenced from the Heinz 1706 tomato, as a number or resources used in tomato genome sequencing, including some of the original DNA libraries, were made using this variety. The researchers also used a wild relative, Solanum pimpinellifolium, which is believed to be the ancestor of the cultivated tomato.

“Because it is the closest wild relative it presents the best opportunity to add through breeding desirable traits while minimising dramatic changes to the otherwise desired attributes.”

The researchers reported in Nature that the sequence from these two tomatoes had 35,000 genes arranged on 12 chromosomes. However, cultivated tomatoes have little genetic variation, so the genome sequence derived from any cultivated tomato would be highly similar to any other.

Even S. pimpinellifolium had a similar genome sequence to that of its cultivated relative, which supports the theory that it is the tomato’s wild ancestor.

One interesting finding was that some of the lost flavour and fruit qualities of tomato is due to breeding for characteristics such as long shelf-life and uniform ripening. These have important storage and visual characteristics, but appear to occur at the expense of flavour, aroma and even nutrient content.

The tomato genome will also help scientists understand the biology of other fleshy fruits. Despite the variation in appearance, fleshy fruits possess similar features, including a change of colour and texture when ripening, the production of aroma volatiles and their nutrient content.

“Many of the genes regulating these processes are conserved among different fruit species,” Giovannoni says. “Understanding the genes and genome activities that underlie tomato fruit biology will in many cases point to the types of genes responsible for these attributes in different species.”

Science Illustrated fact: according to the US Supreme Court, tomatoes are not fruits, but vegetables (for tax purposes at least). Blame it on the 1883 Tariff Act in which taxes were imposed on imported vegetables but not on imported fruits.

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