Spicy Tomato: Brazilian Scientists Are Genetically Engineering Heat

Between spicy arrabbiata sauce and hot red curries, you’d be hard-pressed to find a tomato dish that isn’t made tastier with a bit of heat. The classic combo normally involves throwing in a few peppers with some beefsteaks or plums, but that could change if a project proposed by a team of Brazilian scientists gets the green light. As they argue in an opinion article in Trends in Plant Science on Monday, the time is ripe for a genetically engineered spicy tomato.

With the paper, the team announces its intention to engineer one, but serving up red-hot dishes isn’t its main objective. Capsaicinoids, the spicy compounds in peppers, are nutritionally valuable and useful to industries like pharmaceuticals and weaponry, but peppers are notoriously hard to cultivate on a large scale. Tomatoes, meanwhile, are a reliable crop. Combining the two could yield an industrially useful plant — and shed light on a poorly understood aspect of hot pepper biology.

“We thought it would be fun if we could merge them into one single research line,” senior author Agustín Zsögön, Ph.D., a plant physiologist at the Federal University of Viçosa in Brazil, tells Inverse.

Tomatoes and capsaicin-containing peppers, both part of the Solanaceae family, shared an evolutionary ancestor until about 19 million years ago. The split created the sweet-tart tomatoes we know today, as well as their spicy cousins, the chili peppers, which developed capsaicinoids to punish predators. Tomatoes actually still carry the genes that produce the capsaicinoids in chili peppers, only they’re dormant. But because we now have precise gene editing tools like CRISPR-Cas9, the team argues, those genes don’t have to stay silent.

"“We are still at a loss to explain why some pepper varieties are hotter than others."

If scientists could engineer a reliably-growing tomato plant that produces loads of capsaicinoids, it’d be valuable both inside the kitchen and out. Capsicum fruits, the authors note, have high levels of vitamins A and C, and the capsaicinoid molecules have anti-inflammatory, antioxidant, anti-tumor, and weight-loss properties. Pure capsaicin is also used in pepper spray.

Zsögön and his colleagues, whose interest in tomatoes and peppers stems from the fact that they’re traditional South American crops, recently published a paper in Nature Biotechnology showing how to “domesticate” a wild tomato using only gene editing. While today’s big, red, nutrient-rich tomatoes are the result of many generations of selective breeding, Zsögön and his team knew enough about the tomato genome that they used CRISPR-Cas9 to yield the same effect in one step. Through their mission to engineer a spicy tomato, they hope to complete the Capsicum genome, helping scientists better understand how chili peppers get their heat.

“Capsaicinoid biosynthesis is quite a complex pathway and not sufficiently understood,” Zsögön explains. “For many years, the holy grail was the enzyme controlling the last biochemical step of the pathway, called capsaicin synthase. Upon much effort, the gene coding for this enzyme was eventually identified. Variation in the sequence of this gene is the reason for the variation between hot and sweet peppers.”

"“I would probably use [it] to make hot guacamole."

Through this new project, Zsögön and his team hope to fill in what scientists still don’t know about capsaicinoid production. “For instance, we are still at a loss to explain why some pepper varieties are hotter than others,” he says.

If the team successfully engineers a spicy tomato, the study authors write, it would represent an “important proof-of-concept that could be extended to the production of other valuable metabolites in tomato in the future.” In other words, tomatoes could prove to be an important vehicle for other compounds, like bixin (a reddish chemical used in cosmetics) and beta-carotene, an important antioxidant.

It would, of course, also be a welcome addition to many kitchens. “I would probably use [it] to make hot guacamole,” Zsögön says. “I love Mexican food.”