The scientists of the aptly-named Tomato Genome Consortium have successfully sequenced the genome of the domestic tomato (Solanum lycopersicum), specifically the domestic cultivar known as Heinz 1706. The genome is made up of 35,000 genes spread over 12 chromosomes. In addition to presenting a "high quality" genome of the species, the researches also produced a draft sequence of its closest wild relative, the currant tomato (Solanum pimpinellifolium).
By comparing both genomes with those of the potato, rice and grape, the team was able to draw conclusions as to the tomato's evolutionary heritage, finding that the plant has undergone two genetic triplications during its 120 million-year evolution. One of these triplications occurred before tomatoes and grapes diverged along different evolutionary paths, the second before tomatoes and potatoes split from their common ancestor (the fruit of a potato plant are rather like small green tomatoes). These triplications have a direct effect on the color and fleshiness of the fruit of the species.
Genetic triplications are a form of genetic duplication, a process by which DNA regions containing a gene are copied. These copies are very often free to mutate without posing problems for the species. Over many generations, these copies accrue more genetic mutations than organisms with a single copy of the gene would. A genome exhibiting genetic triplication, then, is one where such duplication has occurred twice, giving two extra copies of a gene, or three in total.
"For any characteristic of the tomato, whether it's taste, natural pest resistance or nutritional content, we've captured virtually all those genes," said Cornell University's James Giovannoni. "Now we can start asking a lot more interesting questions about fruit biology, disease resistance, root development and nutritional qualities," he added.
Though the sequencing of the Heinz 1706 cost in the millions of dollars, this should be reduced by several orders of magnitude for subsequent varieties. The development should assist farmers in selectively breeding tomatoes for particular traits such as yield, disease resistance and flavor. It's claimed that this new information may also be applicable to other fruit species, including apples, bananas and strawberries, which have genetic information in common with the tomato.
The research has been presented in Nature. Lukas Mueller and his team at Cornell's Boyce Thompson Institute have also made information available on the website solgenomics. The genome sequencing itself was carried out by Zhangjun Fei and Joyce Van Eck of the Boyce Thompson Institute, with assistance from Colorado State, Cold Spring Harbor Laboratory, Montana State, the USDA, and the Universities of Arizona, Delaware, Georgia and Tennessee.
