Engineering sweeter tomatoes without sacrificing size

Tomatoes could be made sweeter without sacrificing their weight or yield by altering two genes, according to a study published in Nature. The findings shed light on the genetic and molecular mechanisms underlying sugar accumulation in tomatoes.

Most consumers prefer sweeter tomatoes and higher sugar content increases the economic value for the tomato processing industry. However, genetic linkage often makes it difficult to achieve both sweetness and size in tomato plants. During the domestication of tomatoes, breeders have prioritized fruit size, resulting in fruits that are now 10–100 times larger than their wild ancestor, at the expense of sweetness. An important objective of modern tomato breeding is to increase fruit sugar concentration while at least maintaining, if not increasing, the fruit size, which has proven challenging.

Sanwen Huang and colleagues compared cultivated and wild tomato species and identified two genes, SlCDPK27 and SlCDPK26, as key regulators of sugar accumulation in tomatoes. The proteins encoded by these genes interact with and enhance the degradation of an enzyme responsible for sucrose production. Using CRISPR technology to knock out SlCDPK27 and SlCDPK26 in tomatoes, the researchers report an increase in glucose and fructose levels by up to 30% in the fruit, without reducing weight or yield from the plants. However, the gene-edited tomatoes produced fewer and lighter seeds, although they note that seed health and germination rates were minimally affected.

The authors also found that SlCDPK27 and SlCDPK26 are conserved across a range of plant species, suggesting that the findings could potentially be applied to other crops. In an accompanying News & Views article, Amy Lanctot and Patrick Shih comment that the “work represents an exciting step forward in the understanding of resource partitioning in the fruit, and its implications for crop improvement worldwide.”