Gene-edited tomatoes achieve increased sweetness without loss of size or yield

In a groundbreaking study published in the journal Nature, researchers have successfully used gene editing to create sweeter tomatoes without compromising their size or yield. By knocking out two specific genes using the CRISPR-Cas9 tool, the scientists achieved an increase in glucose and fructose levels of up to 30% in the tomatoes. This development addresses a longstanding issue in tomato breeding where efforts to boost sweetness often resulted in smaller fruit or reduced yields.

Domesticated tomatoes grown industrially have been bred for high yields, resulting in varieties that are 10 to 100 times bigger than their wild ancestors, which produce tiny, cherry-sized fruit. However, this increase in size has come at the expense of sweetness. As Jinzhe Zhang at the Chinese Academy of Agricultural Sciences in Beijing states, "The bigger a tomato is, the lower its sugar content usually is."

Most consumers prefer sweeter fruits, but commercial tomato varieties usually have low sugar content because it is correlated with size, a result of breeding practices prioritizing yield. Researchers have long been interested in overcoming this negative relationship between size and sweetness in tomatoes.

The research team, led by Professor Sanwen Huang, director general of the Agricultural Genomics Institute in Shenzhen, China, identified two genes, SlCDPK27 and SlCDPK26, that inhibit sugar production and accumulation in tomatoes. These genes are more active in large tomato varieties and interact with an enzyme responsible for sucrose production, enhancing its degradation. Using the CRISPR-Cas9 gene-editing tool, the scientists knocked out these genes in domesticated tomato plants, resulting in fruit with up to 30% higher sugar content without reducing size or yield.

"Our discovery of the sugar brake genes leads to [breeding of a] sweeter tomato without sacrificing fruit size and yield, breaking the negative relationship between yield and quality," Professor Huang stated. The gene-edited tomatoes also produced fewer and lighter seeds, but there was no significant difference in fruit weight or yield compared to unmodified plants, and the seeds germinated normally. This suggests that the modification preserved the plants' health and productivity while enhancing sweetness.

The versions of these genes associated with high sweetness are prevalent in wild tomato plants but have largely been lost in modern cultivated varieties. By restoring these gene functions, the researchers were able to increase sugar accumulation in the fruit. The genes are conserved in various plant species, suggesting that the findings could potentially be applied to other crops.

"We are working with some companies to develop some commercial varieties by knocking out these genes. It is still at the beginning stages," Zhang said. He also noted, "They simply taste like tomatoes, but a little sweeter."

"The work represents an exciting step forward in the understanding of resource partitioning in the fruit, and its implications for crop improvement worldwide," an accompanying article published in Nature by Amy Lanctot and Patrick Shih noted. 

Efforts to boost the sweetness of larger tomato varieties have previously had downsides, such as lowering yields. The new approach overcomes these issues by targeting specific genes that regulate sugar accumulation without affecting other traits. The gene-edited tomatoes were rated as sweeter in taste tests, and consumers could determine that the modified tomatoes were sweeter.

The research demonstrates the value hidden in the genomes of crop species varieties and their wild relatives. Mining the genomes of non-domesticated relatives reveals how these genomes can act as repositories for variation that no longer exists in the crop genome. This variation can affect key agriculturally relevant characteristics.

Zhang emphasized the potential for further improvement, stating, "There are still many important genes that regulate sugar waiting to be discovered." The team hopes that CRISPR-edited "sweetness-promoting" tomatoes may be available to consumers in the near future.

Sources: New Scientist, The Independent, Primera Hora, The Guardian, EL PAÍS, Nature

This article was written in collaboration with generative AI company Alchemiq