GMO tweaked tomatoes
The genetic tweaks don't significantly affect color and may preserve flavor, according to a new study

In an attempt to produce plump, tasty tomatoes with longer shelf lives, scientists have successfully tweaked a gene that slows how quickly the fruits soften without affecting their size or color.

The genetically modified tomatoes, described in a paper published Monday in the journal Nature Biotechnology, didn't show telltale signs of softening, like pruned skin, 14 days after harvesting, compared with wrinkled ones from normal plants. To engineer them, the researchers turned to two DNA-altering techniques, including CRISPR-Cas 9, an editing tool used to snip out and replace unwanted genes.

The number of tomatoes growing on genetically modified and normal plants was roughly the same. Plus, the modified plants and normal controls had similar amounts of molecules known to affect taste, color, and smell, according to the study.

How the new tomatoes taste is still an unsolved mystery. Because consuming genetically modified foods isn't allowed in the U.K., where the research was conducted, the scientists didn't sample their produce, said Graham Seymour, a plant biotechnologist at the University of Nottingham and the study's lead author.

"The current work is potentially important because it only slows down one aspect of ripening—softening—that is critical to shipping and shelf life," said Harry Klee, a horticultural-sciences professor at the University of Florida in Gainesville who wasn't involved with the research.

Soft tomatoes are easily crushed, which impacts their salability. In the U.S., the market for fresh and processed tomatoes is about $2 billion, according to the U.S. Department of Agriculture.

As fruits ripen, enzymes break down the component of cells that make them tough, known as cell walls. The fruits also change color, emit pleasing aromas and become sweeter.

That creates a chemical conundrum for fruit designers: putting the brakes on softening also diminishes flavor. Most commercial attempts at genetic modification haven't struck the right balance. So for decades, academics and industrial growers have continued the hunt for genes they could tweak to achieve both.

In the new study, which was funded in part by pesticide and seed company Syngenta AG, the researchers homed in on a gene for pectate lyase, an enzyme that chews up cell walls. (Syngenta declined to comment.)

Targeting cell wall-related genes is "a promising approach" to improve shelf life without affecting quality, said Jose Mercado, a biotechnologist at the University of Malaga in Spain who has studied pectate lyase's role in strawberry softening but wasn't involved in the new study.

In 2010, he noted, scientists from India suppressed enzymes involved in breaking down common cell-wall proteins and grew firmer, longer-lasting tomatoes.

It's unlikely the same DNA-wrangling technologies will be used for tomatoes grown commercially. The tomato market isn't big enough to "justify the cost of going through the regulatory hoops" necessary to sell genetically modified tomatoes, said USDA plant molecular biologist James Giovannoni. "That is why the GMOs [genetically modified organisms] currently in the market are major crops, like maize or soy."

The research's benefit is providing a road map to genes breeders could target. It's more likely they would cross tomatoes with less pectate-lyase activity to commercial varieties and select those that are firm and tasty, he added.

That will require growers to figure out what conditions give them optimal flavor and texture, at the right harvest time.

"That's something you can only do empirically," Dr. Seymour said. The testing, he added, needs to be done by growers. His lab will continue working on improving tomato quality. His newly published study is part of a larger collaboration with Syngenta on optimizing color and texture.