Scientists modify tomatoes to make them ‘significantly sweeter’

Glucose and fructose levels were 30% higher after researchers removed two genes that regulate sugar content, according to study

HONG KONG — Chinese scientists have successfully modified tomatoes to make them sweeter by removing two genes that regulate sugar content, according to a new study.

The researchers said the modified tomatoes had glucose and fructose levels that were up to 30% higher than the variety they were based on, but the weight and yield were maintained.

“Our finding of the sugar brake genes … provides a possible solution for improving sugar content without reduction in fruit yield for modern commercial varieties, which are preferred by both consumers and producers,” the team said.

“[The] CRISPR-edited ‘sweetness-promoting’ tomatoes may be available to consumers in the near future,” they wrote in an article published in the peer-reviewed journal Nature on Thursday, referring to a genome editing technology.

The team led by the Chinese Academy of Agricultural Sciences in Beijing includes researchers from other institutes in China and Cornell University in the United States.

Most consumers prefer sweeter fresh tomatoes, and higher sugar levels can also increase the economic value of tomatoes when they are processed into other products.

When producing tomato sauce with a 28% sugar concentration, for example, raising the soluble solids content including sugar from 4 to 5% can reduce the amount of fresh tomatoes needed by up to a quarter, according to the study.

But the genetic links of tomatoes make it a challenge to achieve both sweetness and size.

During crop domestication, breeders focused on increasing the fruit size and cultivated tomatoes that are now 10 to 100 times larger than their wild ancestors. But while the tomatoes are bigger, they are not as sweet.

In the study, the researchers overcame that negative correlation between sugar content and yield with genome editing, which they called “an opportunity to engineer sweeter tomatoes in large-fruited cultivars without sacrificing size or yield”.

They also invited 100 volunteers to taste and compare the edited tomatoes with their original version in Shenzhen and Beijing. The modified tomatoes were found to be “significantly sweeter”.

Lead author Zhang Jinzhe, a researcher with the State Key Laboratory of Vegetable Biobreeding at the Chinese Academy of Agricultural Sciences, said the team had filed a patent on the use of the two genes to improve fruit sugar content.

“We hope to apply the gene-editing technique to different tomato varieties, especially those that are already commercialised and mass-produced, to see how it works on them,” he said, noting that tomatoes on the market were more resistant to disease, more durable in transport and had a longer shelf life than the lab-grown variety.