Altering two genes to produce sweeter tomatoes without sacrificing size, weight or yield

A team of horticulturists, bio-breeders and agriculture specialists affiliated with a host of institutions across China has produced sweeter tomatoes without sacrificing size, weight or yield by altering two of their genes. In their study, published in the journal Nature, the group modified the genes of a tomato variant that coded for proteins that lowered levels of enzymes related to sugar production.

Amy Lanctot and Patrick Shih with the University of California, Berkeley, have published a News and Views piece in the same journal issue outlining the work done by the team in China.

Over the past several centuries, farmers around the world have crossbred tomato plants with the aim of improving yields and increasing fruit size. The result has been a massive growth in both. Unfortunately, making tomatoes bigger has also made them less sweet. Past efforts to make large modern tomatoes sweeter have resulted in smaller yields.

For this new study, the research team took a new approach. They began by looking into the reason for the loss of sweetness in tomatoes and partially corrected crossbreeding effects on the tomato genome.

The research team discovered two genes in multiple tomato variants that were more active in larger varieties. Called SlCDPK26 and SlCDPK27, the two genes were found to code for proteins that lowered the levels of enzymes that produce sugar. The researchers next genetically modified the genome of a variety of large tomato called Money Maker to disable the two genes they had identified.

Plants grown with the modification produced tomatoes with a 30% increase in fructose and glucose levels with no reduction in size or weight. The team further confirmed that the tomatoes were sweeter by tasting them. The gene alterations did not diminish yields—the only other difference they found was that the tomatoes produced fewer seeds, which were also smaller. They suggest consumers would probably like this added feature.

The research team acknowledges that their modified tomatoes are not as sweet as cherry varieties, but suggest further work might lead to more gene changes that could make the biggest tomatoes as sweet as the smallest.

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