Tomato sweetness boosted by gene editing to knock out two genes

Genetically editing sugar-regulating genes increases tomato sweetness, without affecting yield or size. The findings break a long-standing challenge in tomato breeding: balancing taste and productivity, thereby offering potential benefits for both consumers and growers.

Large-fruited commercial tomatoes often have lower sugar content, a consequence of distributing nutrients across larger fruit. Sweeter tomatoes are preferred by consumers and processors are prepared to pay more for them as their increased sugar content reduces the amount of raw material needed for products like tomato sauce.

Researchers led by Sanwen Huang, at the Chinese Academy of Sciences, China, pinpointed the genetic factors influencing sugar content in tomatoes using a genome wide association study. By analysing the genetic makeup of various tomato varieties and correlating it with sugar content, researchers pinpointed a gene locus on chromosome 11 that was strongly associated with higher levels of soluble sugars. Closer examination revealed that the two genes, related as a result of a gene duplication event, act as sugar brakes by phosphorylating and subsequently degrading the enzyme responsible for sugar synthesis, sucrose synthase. They identified a 12-base-pair insertion in the segment of DNA controlling one gene that strongly correlated with higher sugar levels.

To confirm their role, the team used Crispr–Cas9 to knock out these genes, generating mutants that didn’t suppress sugar synthesis. This enhanced glucose and fructose levels by 30% while maintaining desirable fruit size and yield. While the mutants produced fewer and lighter seeds, their germination was not affected. Consumer tests validated the success of this approach, where participants consistently rated the gene-edited tomatoes to be sweeter, compared with traditional varieties. The research could have broader applications for other fruit crops, bridging the gap between flavour and farm economics.