Scientists Have Turned Tomatoes Into A Rich Source Of Vitamin D

Tomatoes get riper and tastier in the summer Sun. Two studies now show that with a little help from gene editing, Sun-ripened tomatoes can also stockpile a precursor molecule to vitamin D, a vital nutrient normally found mainly in animal products, Erik Stokstad reported for Science magazine.

Photo Insert: The experiment should allow each ripe, sliced tomato, after exposure to sunlight, to offer as much previtamin D3 as two medium eggs.

“This could be a game-changer” in nations where vitamin D deficiency is a problem, says Esther van der Knaap, a plant geneticist at the University of Georgia, Athens. Biofortified plants could also help vegans get enough of the nutrient.

The finding opens up a new era for vitamin D, says nutritional scientist Susan Lanham-New of the University of Surrey. Vitamin D helps regulate how the body uses calcium. There is evidence that low levels are linked higher risk of cardiovascular disease and other health problems.

Ultraviolet B (UVB) radiation converts a precursor in the skin into a form that the liver and kidney transform into usable vitamin D. Eating animal products—fish, eggs, and liver—that contain precursors can help make up the deficit. In addition, milk sold in the US and a few other countries is supplemented. For vegans, mushrooms and yeast are less effective sources.

Another option is to take supplement pills, which are often made from lanolin, a waxy substance secreted by sheep.

In the May 24 issue of Nature Plants, a team led by Cathie Martin, a plant metabolic engineer at the John Innes Center, reported that knocking out a single gene created tomatoes which could each provide 20% of the recommended daily allowance of vitamin D in the UK.

And in a late March preprint, a group led by plant geneticist Sunghwa Choe of Seoul National University reported that by knocking out a related gene, it was able to produce tomatoes with even higher levels of a vitamin D precursor.

Normally, tomatoes and other plants in their Solanaceae family make a precursor called provitamin D3 and convert it into other compounds using enzymes coded for by two genes, called 7-DR1 and 7-DR2. By knocking out, or incapacitating, either of these genes would cause the plant to accumulate provitamin D3, which when exposed to sunlight transforms into a second precursor—previtamin D3—that people can use.

“This seemed like a real opportunity,” Martin says. It worked. Martin’s team decided to knock out 7-DR2, which helps the plant synthesize compounds plants use to deal with stress from pests and microbes.

Thanks to the intact 7-DR1, the modified plants grew normally. And each ripe, sliced tomato, after exposure to sunlight, should offer as much previtamin D3 as two medium eggs. Choe’s group knocked out the other gene, 7-DR1, involved in making growth hormones.

In their preprint, posted at Research Square, the researchers estimate that a modified tomato can contain up to 100 micrograms of provitamin D3—more than seen in Martin’s experiments—after a month of freeze-dried storage. “We think that the molecule is pretty stable in the fruit,” Choe says.

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