A second attempt at domesticating the tomato
A
A. The tomato on our plates began as a straggly plant from the Andes of South America, and in the wild it still bears fruit no larger than a pea. Peoples such as the Inca and the Aztec reshaped it across countless generations, saving and breeding from any plant whose genetic make-up had shifted in a helpful direction, so that the fruit slowly grew bigger. This method carried a hidden penalty, though. Each time one favoured individual is lifted out of a larger population to parent the next crop, a share of that crop's genetic diversity vanishes for good. What is more, a welcome mutation often arrives in the company of an unwelcome one: the firm, even-looking tomatoes raised for today's supermarkets have given up much of the flavour their ancestors possessed.
B
B. Turning the wild tomato into a food crop took humans something like three thousand years. Two teams, one in Chile and one in China, have repeated the feat — each in under three years, and in some ways better, since their re-domesticated fruits are more nourishing than what we eat now. They began with comparison: by setting the genomes of modern plants beside those of their wild relatives, scientists had already worked out which genetic changes domestication involved. The teams then reintroduced those changes deliberately, from scratch, while keeping — and sometimes sharpening — the qualities that made the wild strains valuable. Everything depends on CRISPR, a genome-editing technique in which the DNA in a living cell is altered on purpose, so that genetic material can be added, taken out or exchanged. Its advocates believe it could achieve far more than fine-tuning familiar crops; it might turn thousands of untamed plants into food worth growing. A third group, in Canada, has already begun doing just that with a wild relative of the tomato. 'This could change our diet completely,' says Anders Melheim of the University of Aarhus in Denmark, who belongs to the Chilean team. 'Some 50,000 plant species are edible, and yet about nine-tenths of the energy we live on comes from just fifteen crops.' Wenjie Tan, of the Institute of Plant Molecular Biology in Shanghai, sets his sights further off: 'Now that we can copy the domestication route already followed by major crops — rice, maize, sorghum and so on — we can go on to tame plants that have never been domesticated at all.'
C
C. Melheim's group made several edits in total. By rewriting a gene they named PLUMP they made each tomato roughly four times its former weight, and by adjusting a second, which they called CLUSTER, they increased how many fruits each stalk would carry. Ordinary domestication had over the centuries lowered the tomato's lycopene level — the red pigment thought to offer possible health benefits — but the Chilean team drove it upward instead. A wild tomato already contains around twice the lycopene of a cultivated one; their newly built fruit contains roughly six times as much. Melheim is pleased with how they turned out. 'They taste rather good,' he says. 'Quite intense, and marvellously aromatic.'
D
D. The Chinese team went about things differently, giving back to several wild strains the useful qualities that everyday domestication had stripped out. One outcome was a line of tomatoes able to shrug off bacterial speck, a widespread disease capable of ruining much of a harvest. Another was a strain that copes far better with drought and, as a bonus, holds noticeably more vitamin C than usual.
E
E. Working the same way, Marisol Ferreira of the Boyd Institute in Ontario, Canada, set out to domesticate a plant never farmed before — a wild, husk-wrapped berry much like the Cape gooseberry. Berries of this kind already sell in modest amounts, but they are hard to grow: the plant sprawls untidily and its small fruits drop from the branches the moment they ripen. Ferreira's team has edited it to enlarge the berries, give the plant a more compact shape, and keep the ripe fruit from falling. 'There is a real chance this could become a commercial crop,' she says, though she warns that going further would be costly, given the licence fee CRISPR carries and the regulatory approval any new food must win. The method could bring many overlooked plants into wider use, says Rupert Ashworth of the Fenwick Crop Laboratory in Britain; even so, he doubts that many will ever win over farmers and shoppers fully enough to become staple foods. The three teams already eye other candidates for the mainstream — finger-millet, marsh-grass and the pigeon pea among them — and by starting with wild species that already tolerate heat or drought, Tan suggests, they could build crops that thrive even as the world warms. Melheim, though, would not name the species his own team was pursuing, precisely because CRISPR has made the work so easy. 'Anyone with the right skills could walk into their lab and do this.'
