The researchers used gene editing to turn off a specific molecule in the plant’s genome that increased provitamin D3 in the fruits and leaves of tomato plants. It was then converted into vitamin D3 by exposure to UVB light.
Vitamin D is created in our body after the skin is exposed to UVB rays, but the main source is food. This new biofortified crop could help millions of people suffering from vitamin D insufficiency, a growing problem linked to a higher risk of cancer, dementia and many leading causes of death. Studies have also shown that vitamin D deficiency is linked to increased severity of Covid-19 infection.
Tomatoes naturally contain one of the building blocks of vitamin D3, called provitamin D3 or 7-dehydrocholesterol (7-DHC), in their leaves at very low levels. Provitamin D3 does not normally accumulate in ripe tomatoes.
Researchers in Professor Cathie Martin’s group at the John Innes Center used CRISPR-Cas9 gene editing to edit the genetic code of tomato plants so that provitamin D3 accumulates in the tomato fruit. The leaves of the modified plants contained up to 600 ug of provitamin D3 per gram of dry weight. The recommended daily intake of vitamin D is 10 ug for adults.
When growing tomatoes, the leaves are usually waste, but those from engineered plants could be used to make vegan-friendly vitamin D3 supplements or for food fortification.
“We have shown that you can biofortify tomatoes with provitamin D3 using gene editing, which means tomatoes could be developed as a sustainable plant source of vitamin D3,” said author Professor Cathie Martin. correspondent of the study published in Nature. Plants.
“Forty percent of Europeans suffer from vitamin D deficiency, as do a billion people worldwide. Not only are we tackling a huge health problem, but we’re helping growers because the tomato leaves that are currently wasted could be used to make supplements from the genetically modified lines.
Previous research has investigated the biochemical pathway of how 7-DHC is used in the fruit to make molecules and found that a particular Sl7-DR2 enzyme is responsible for converting it into other molecules.
To take advantage of this, the researchers used CRISPR-Cas 9 to deactivate this Sl7-DR2 enzyme in tomato so that 7DHC accumulates in the tomato fruit.
They measured the amount of 7-DHC in the leaves and fruits of these modified tomato plants and found that there was a substantial increase in 7-DHC levels in the leaves and fruits of the modified plants.
7-DHC accumulates in the flesh and skin of tomatoes.
The researchers then tested whether 7-DHC from the modified plants could be converted into vitamin D3 by shining UVB light on the leaves and sliced fruit for 1 hour. They found that it did and that it was very effective.
After UVB treatment to convert 7-DHC to vitamin D3, one tomato contained the equivalent levels of vitamin D of two medium-sized eggs or 28g of tuna, both of which are recommended dietary sources of vitamin D.
The study indicates that vitamin D in ripe fruit could be further increased by prolonged UVB exposure, for example during sun-drying.
Blocking the enzyme in tomato had no effect on the growth, development or yield of tomato plants. Other closely related plants such as eggplant, potato and pepper have the same biochemical pathway, so the method could be applied to these vegetable crops.
Earlier this month, the UK government announced an official review to determine whether foods and drinks should be fortified with vitamin D to tackle 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 in higher latitudes, people need to get vitamin D from their diet or supplements because the sun is not strong enough for the body to produce it naturally.
Study first author Dr Jie Li said: “The Covid-19 pandemic has helped highlight the problem of vitamin D insufficiency and its impact on our immune function and overall health. The provitamin D-enriched tomatoes we’ve produced provide an essential plant source of the sunshine vitamin. This is great news for people who follow a plant-rich, vegetarian or vegan diet, and for the growing number of people around the world suffering from the problem of vitamin D deficiency.”
Reference: Li J, Scarano A, González NM, et al. Biofortified tomatoes offer a new path to vitamin D sufficiency. natural plants. Published online May 23, 2022: 1-6. doi:10.1038/s41477-022-01154-6
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