Chinese researchers: Sweeter tomatoes without smaller size

Who doesn't know the classic, almost tasteless tomato? They often come from the greenhouse, have a (large) standard size and are abundantly watery. They are nice to look at, but flavor looks different. What is missing is the sweetness that is much more common in wild tomatoes. But how can a rich, supermarket-ready harvest be combined with good taste? It turns out that the CRISPR gene scissors, which are already being used in the production of new forms of therapy, can help.

Stepping on the gas when it comes to sugar content – for more flavor

CRISPR makes it possible to cut out parts of the genome and replace them with another piece of DNA. Experiments have already been carried out with crops that then require less acreage or less sunlight, for example. It is also possible to increase the nutrient content or reduce the amount of water required for planting. A team led by Chinese researcher Sanwen Huang at the Chinese Academy of Agricultural Sciences in Beijing has now compared classic greenhouse tomatoes with various wild species. They discovered a total of two genes that appear to be specifically involved in sugar formation in tomatoes. The proteins encoded by these genes interact with enzymes that are responsible for the production of sucrose.

The study, published last month in Nature, shows how the "sugar brakes" could be solved. "The sugar content of commercial varieties is generally low [in tomatoes] because it is inversely correlated with fruit size and growers prioritize yield over flavor quality. We have identified two genes, calcium-dependent protein kinase 27 (SlCDPK27; also known as SlCPK27) and its paralog SlCDPK26, that control fruit sugar content. They act as sugar brakes by phosphorylating a sucrose synthase, which promotes the degradation of the sucrose synthase," it says. By using CRISPR, the two genes could be switched off. In the experiment, the result was a 30 percent increase in glucose and fructose. This was clearly evident in the taste test – at the same time, there were no restrictions in terms of size and harvest.

Too little knowledge about what actually happens in plants

Interestingly, SlCDPK27 and SlCDPK26 appear to influence sugar accumulation not only in tomatoes, but also in other crops. Further studies will focus on sweeter apples and pears in the future. In a "News & Views" article accompanying the study, researchers Amy Lanctot and Patrick Shih say that the work represents an "exciting step forward" in understanding resource allocation in the fruit. This could have "implications for crop improvement worldwide". According to Shih, there is currently still a general lack of understanding of "how plants fundamentally work". In any case, the issue of sugar content in tomatoes has occupied plant biologists for many years without a solution being found. "The genetic, molecular and biochemical characterization of wild tomato species with high fruit sugar content has significantly improved our understanding of carbohydrate metabolism in tomatoes and could be used for new breeding programs," Huang and Co. continue.

As is usually the case with genetic engineering, the safety of the plants must first be verified. CRISPR does not change this, even if the study is a knockout trial in which no new genes are added and only the two sugar brakes are switched off. However, this could also have negative consequences that need to be researched. Work on tomato cultivation itself is also continuing unabated. Also in November, British researchers showed how they can improve the lighting in greenhouses by using a spray that can change color wavelengths, allowing them to get by with less artificial light. This would significantly reduce electricity consumption during cultivation in winter. If the spray is sprayed onto greenhouse panes, blue light from outside is converted into red light, which in turn helps the plants to grow.

(nie)