Tomatoes genetically engineered to produce vitamin D, known as the sunshine vitamin, could be a simple and sustainable innovation to tackle a global health problem.
Researchers used gene editing to turn off a specific molecule in the plant’s genome, increasing provitamin D3 in both the fruit and leaves of tomato plants. It was then converted to vitamin D3 by exposure to UVB light.
Vitamin D is produced in our bodies after our skin is exposed to UVB light, but the main source is food. This new bioenhanced crop could help millions of people with vitamin D deficiency, a growing problem linked to an increased risk of cancer, dementia and many leading causes of death. Research has also shown that vitamin D deficiency is linked to an increased severity of infection from Covid-19.
Tomatoes naturally contain one of the building blocks of vitamin D3, provitamin D3 or 7-dehydrocholesterol (7-DHC), in their leaves in very low levels. However, provitamin D3 does not normally accumulate in ripe tomato fruits.
Scientists in Professor Cathie Martin’s group at the John Innes Center used CRISPR-Cas9 gene editing to make revisions to the genetic code of tomato plants so that provitamin D3 accumulates in the tomato fruit. The leaves of the processed plants contain up to 600 µg (micrograms) of provitamin D3 per gram of dry weight. The recommended daily intake of vitamin D is 10 µg for adults.
When growing tomatoes, leaves are usually waste material, but those from the processed plants can be used to produce vegan vitamin D3 supplements or for food fortification.
“We have shown that you can biofortify tomatoes with provitamin D3 through gene editing, which means that tomatoes can be developed as a plant-based, sustainable source of vitamin D3,” said Professor Cathie Martin, corresponding author of the study appearing in Nature. Plants.
“Forty percent of Europeans have a vitamin D deficiency and so do a billion people worldwide. Not only are we tackling a huge health problem, but we are helping producers because tomato leaves that are currently being thrown away can be used to make supplements from the gene-edited lines.”
Previous research has studied the biochemical pathway of how 7-DHC is used in the fruit to make molecules and found that a particular enzyme, Sl7-DR2 is responsible for converting it into other molecules.
To take advantage of this, the researchers used CRISPR-Cas 9 to disable this Sl7-DR2 enzyme in tomato, so that the 7DHC accumulates in the tomato fruit.
They measured how much 7-DHC was in the leaves and fruits of these processed tomato plants and found that there was a substantial increase in 7-DHC in both the leaves and fruits of the processed plants.
The 7-DHC accumulates in both the pulp and skin of the tomatoes.
The researchers then tested whether the 7-DHC in the processed plants could be converted to vitamin D3 by shining UVB light on leaves and sliced fruit for 1 hour. They found it did and was very effective.
After being treated with UVB light to convert the 7-DHC into vitamin D3, one tomato contained the equivalent vitamin D content as two medium eggs or 28 g of tuna – both recommended dietary sources of vitamin D.
The study says that vitamin D in ripe fruit can be further increased by prolonged exposure to UVB, for example while drying in the sun.
Blocking the enzyme in the tomato had no effect on the growth, development or yield of the tomato plants. Other closely related plants such as eggplant, potato and pepper share the same biochemical pathway, so the method can be applied to these vegetable crops.
Earlier this month, the UK government announced an official review to examine whether food and drink should be fortified with vitamin D to address health inequalities.
Most foods are low in vitamin D and plants are generally very poor sources. Vitamin D3 is the most bioavailable form of vitamin D and is produced in the body when the skin is exposed to sunlight. In winter and at higher latitudes, people must get vitamin D from their diets or supplements because the sun is not strong enough for the body to make it naturally.
The study’s lead author, Dr. Jie Li, said: “The Covid-19 pandemic has helped raise awareness of the problem of vitamin D deficiency and its impact on our immune function and general health. The provitamin D-enriched tomatoes we’ve produced provide a much-needed plant-based source of the sunshine vitamin. That’s great news for people who follow a plant-based, vegetarian or vegan diet, and for the growing number of people worldwide who suffer from the problem of vitamin D deficiency.”
Reference: “Biofortified tomatoes offer a new route to vitamin D adequacy” by Jie Li, Aurelia Scarano, Nestor Mora Gonzalez, Fabio D’Orso, Yajuan Yue, Krisztian Nemeth, Gerhard Saalbach, Lionel Hill, Angelo Santino and Cathie Martin, 23 May , Nature Plants†