TOMATOES TAMED AGAIN WITH "CRISPR"

Gene editing opens the way to healthier crops.

It took at least 3000 years to domesticate the tomato. Now two teams, one in China, the other in Brazil, Germany and the US, have done it all over again in less than three years – only better in some ways because their tomatoes are more nutritious than those we currently eat.

This approach, which relies on the CRISPR genome-editing technique, could not only improve existing crops, but could also be used to turn thousands of wild plants into new crops. A third team in the US has already begun to do this with a relative of the tomato called the ground cherry.

This fast-track domestication could help make the world’s food supply healthier and far more resilient to climate change and diseases, such as the rust fungus devastating wheat crops.

“This could transform what we eat,” says Jörg Kudla at the University of Münster in Germany, a member of the international team that worked on the tomato. “There are 50,000 edible plants in the world, but 90 per cent of our energy comes from just 15 crops.”

Wild tomatoes, native to the Andes mountains in South America, produce pea-sized fruit. Over many generations, people transformed the plant by picking mutants with desirable traits such as larger fruit.

But when a single mutant is plucked from a larger population for breeding, genetic diversity is lost. And the desirable mutations sometimes come with unwanted traits. For instance, the tomatoes grown for supermarkets have lost much of their flavour.

By comparing the genomes of food plants with their wild relatives, biologists are working out what changes occurred in domestication. The two teams of tomato researchers have used this knowledge to reintroduce these changes from scratch while maintaining or even enhancing the desirable traits of wild strains.

Kudla’s team made six changes. For instance, they tripled the size of fruit by editing a gene called FW2.2, and got more tomatoes per truss by editing another called MULT (Nature Biotechnology, doi. org/cvf2).

The historical domestication of tomatoes led to lower levels of the red pigment lycopene, which is thought to be good for us. The international team boosted it instead. Wild tomatoes have twice as much lycopene as cultivated ones. The newly domesticated one has five times as much.

“They are quite tasty,” says Kudla. “And very aromatic.”

The researchers in China re-domesticated several strains of wild tomatoes with desirable traits lost in domestication. In this way they managed to make a strain resistant to a disease called bacterial spot race. They also created another strain that is more salt tolerant and one with higher levels of vitamin C (Nature Biotechnology, doi.org/cvfz).

“We will taste them when the plants are mature”, in a few weeks, says Caixia Gao at the Chinese Academy of Sciences in Beijing.

New commercial crops

Meanwhile, Joyce Van Eck at the Boyce Thompson Institute in New York state and her colleagues are using the same approach to domesticate the ground cherry (Physalis pruinosa) for the first time (Nature Plants, doi.org/cvfx).

Ground cherries are already sold to some extent in US farmers’ markets, but they are hard to produce because the plant has a sprawling growth and the small fruit drop off when ripe. Van Eck’s team edited the plants to increase fruit size, make growth more compact and stop fruit falling off.

“There’s potential for this to be a commercial crop,” says Van Eck. But taking the work further would be expensive because of the need to pay for a CRISPR licence and get regulatory approval.

This approach could boost the use of many obscure plants, says Jonathan Jones of the Sainsbury Laboratory in the UK. But it will be hard for them to get so popular they become new staples, he says.

The three teams are already eyeing other plants that could, in the words of Van Eck’s team, be “catapulted into the mainstream”, including foxtail, oat grass and amaranth. By choosing wild plants that are drought or heat tolerant, says Gao, we could create crops that will thrive even as the planet warms.

Kudla didn’t want to reveal which species were in his team’s sights, because CRISPR has made it so easy. “Anyone with the right skills could go home to their lab and do this.”

By Michael Le Page in "New Scientist", UK, vol.240, no. 3198, October, 6, 2018, excerp p.6. Digitized, adapted and illustrated to be posted by Leopoldo Costa.