The world produces around 180 million tons of tomatoes each year. Whether they are raw, cooked, or used in sauces, tomatoes are a staple in kitchens worldwide. However, not all tomatoes are created equal — some are much tastier than others. Generally, the sweeter the tomato, the better the taste. Yet, for decades, the challenge has been that sweeter tomatoes often yield lower harvests.

That, however, might be about to change.

A new study published in Nature reveals that targeted gene editing can significantly boost the sugar content of tomatoes without compromising fruit size or yield. This breakthrough is good news for consumers who prefer sweeter tomatoes and for the agricultural industry, which has long struggled with the trade-off between sweetness and productivity.

Like many other crops, modern tomato varieties are bred for size and yield rather than taste. As a result, there’s a big difference between the flavors of cultivars grown for high yields and those grown for their taste. For breeders and farmers, increasing one usually means sacrificing the other. Prof. Sanwen Huang, the director general of the agricultural genomics institute at the Chinese Academy of Agricultural Science, Shenzhen, thinks we can do better.

Huang and colleagues analyzed the genetic basis of sweetness in tomatoes when they discovered two key genes: SlCDPK27 and SlCDPK26. These genes act like “sugar brakes,” reducing sugar accumulation in the fruit during ripening. They realized that if they “release” these breaks, tomatoes could become much sweeter.

They used CRISPR-Cas9 gene-editing technology to “knock out” these genes in several tomato varieties. The results were impressive. Sugar levels, particularly glucose and fructose, increased by up to 30%, while the fruit size and overall yield remained unaffected. These gene-edited tomatoes were not only sweeter but also maintained the same level of productivity as their unedited counterparts.

How CRISPR Editing Boosts Sweetness

CRISPR-Cas9 is a powerful gene-editing tool that allows scientists to modify DNA in living organisms precisely. It works like molecular scissors, using a guide RNA to target specific sequences in the genome and the Cas9 enzyme to cut the DNA at that location. This allows researchers to delete, insert, or alter genetic material with high precision.

The technology is already used to treat conditions in humans (like sickle cell disease) and researchers say there’s a lot of potential in agriculture as well.

Firstly, however, you need to understand how the genes work. Both SlCDPK27 and SlCDPK26 were found to interact with a critical enzyme called sucrose synthase (SlSUS3). This enzyme plays a central role in breaking down sucrose into glucose and fructose. The more the genes interact with SISUS3, the less sugar content there was in the tomato — what’s why the genes act as a “sugar brake.”

When the scientists knocked out these sugar brake genes, they effectively removed the inhibition on sucrose synthase. This allowed the tomatoes to accumulate higher levels of glucose and fructose, enhancing their sweetness without affecting fruit weight or yield. The edited tomatoes had approximately 16% higher total soluble solids content, which is a key indicator of fruit sweetness.

Nothing else seemed to change regarding the tomatoes. The gene-edited tomatoes maintained the same levels of essential nutrients and vitamins.

Are gene-edited tomatoes sweet for consumers?

To validate the improved sweetness, the researchers conducted large-scale taste tests in Beijing and Shenzhen.

They recruited over 200 volunteers for the trials. Participants consistently rated the gene-edited tomatoes as significantly sweeter than the unedited controls, demonstrating that the genetic modifications not only improved measurable sugar levels but also enhanced the sensory appeal of the tomatoes.

But will the edited tomatoes truly be palatable for consumers worldwide?

Huang is confident. He says the new tomatoes could be on the shelves within 3-5 years, citing that other gene-edited tomatoes are already for sale in Japan. Unlike traditional crossbreeding, which can take years to achieve desired traits, CRISPR technology allows scientists to make precise changes in a much shorter timeframe. However, it may not all be about the taste.

Historically, gene-edited crops have been immensely unpopular. However, CRISPR-edited crops have been gaining acceptance in some regions. Gene-edited salad greens are coming to US stores and indeed, countries like Japan have been selling gene-edited veggies for a few years already. Even the European Union, arguably the most heavily regulated region in the world, has voted to ease regulations on gene-edited crops.

While it won’t happen overnight, the public’s reluctance seems to be waning as well, as the advantages of gene-edited crops become clearer. Tomato enthusiasts have reasons for optimism. A future where sweeter, more flavorful tomatoes become the norm rather than the exception may be just around the corner.

The study was published in Nature.