A research team is developing genetically modified tomatoes as a rich source of vitamin D. Switching off a gene is expected to increase the concentration of a precursor of the essential nutrient. Normally, tomatoes ripen and become tastier in the summer sun. Now the new research shows that sun-ripened tomato varieties can also accumulate a precursor molecule of vitamin D3 with a little help from genetic engineering. This is a vital provitamin normally found mainly in animal products. In addition, the modified tomato plants contain as much provitamin D3 as two eggs or a tablespoon of tuna.
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Boosting vitamin D levels through genetically modified tomatoes
According to the scientists, this may be a game changer, especially in countries where vitamin D deficiency is a problem . Such modified plants could also help vegans get enough of the so-called sunshine vitamin. In addition, nutritionists say the finding opens up new and exciting possibilities for people with vitamin deficiencies. Vitamin D, for example, helps regulate how the body uses calcium, leading to stronger bones. Evidence also still suggests that low levels are associated with a higher risk of cardiovascular disease and other health problems.
Sunlight can cause the body to synthesize the sunshine vitamin because ultraviolet B (UVB) radiation converts a precursor in the skin into a form that the liver and kidneys convert into usable vitamin D. People living at high latitudes are often not exposed to enough UVB, especially in winter, to avoid vitamin D deficiency. Age or darker skin can also slow vitamin D synthesis. The researchers used gene editing to knock out a specific molecule in the plant’s genome that increased provitamin D3 in both fruit and leaves of tomato plants. It was then converted to vitamin D3 by exposure to UVB light.
Potential benefits for medicine
Since the main source of vitamin D is food, the new research may help develop treatment strategies. Such genetically modified tomatoes and such enriched plants could help millions of people with vitamin D deficiency. As mentioned above, this is a growing problem associated with increased cancer risk, dementia, and many leading causes of death.
Scientific research has also shown that vitamin D deficiency is associated with increased severity of covid-19 infection. In addition, tomatoes that produce vitamin D could be a simple and sustainable innovation to address a global health problem. They naturally contain one of the building blocks of vitamin D3, called provitamin D3 or 7-dehydrocholesterol (7-DHC), in their leaves in very small amounts. However, provitamin D3 does not normally accumulate in ripe tomato fruit.
How a research team was able to develop genetically modified tomatoes
Scientists in Professor Cathie Martin’s group at the John Innes Center used CRISPR-Cas9 gene editing to revise the genetic code of tomato plants to accumulate provitamin D3 in tomato fruit. Leaves from the edited plants contained up to 600 ug (micrograms) of provitamin D3 per gram of dry weight. The recommended daily intake of vitamin D is 10 ug for adults. When tomatoes are grown, the leaves are usually waste material, but those of the modified tomato plants could be used to make vitamin D3 supplements for vegans or to fortify foods. Previous research has investigated the biochemical pathway of how 7-DHC is used in the fruit to make molecules. They found that a specific enzyme Sl7-DR2 is responsible for converting it into other molecules.
To take advantage of this, the researchers used CRISPR-Cas 9, which allowed them to knock out the Sl7-DR2 enzyme in tomatoes, allowing the 7DHC to accumulate in the tomato fruit. They measured how much 7-DHC was present in the leaves and fruits of these edited tomato plants. The team found that the 7-DHC content had increased significantly in both the leaves and fruits of the processed plants. The 7-DHC accumulates in both the pulp and the skin of the tomatoes. After treatment with UVB light to convert the 7-DHC to vitamin D3, one tomato contained the same amount of vitamin D as two medium eggs or 28 g of tuna – recommended dietary sources of vitamin D.
So far, the modified tomatoes have only been grown in laboratory greenhouses. The study authors will begin a field trial in July 2022 and hope to start this summer. Field testing will be critical to see if the plants can thrive under real-world stress. Researchers also need to show that the body can absorb the provitamin D3 in the tomatoes and convert it to vitamin D.
Another challenge could be consumer acceptance. Some people may not accept genetically modified tomatoes. However, if the plants make it to market, plant physiologists could mark a leap forward in reducing dependence on animal foods.
This new study says that vitamin D in ripe fruit could be further increased by prolonged exposure to UVB, such as during sun drying. Blocking the enzyme in tomato had no effect on growth, development or yield of tomato plants. Other closely related crops such as eggplant, potato and bell pepper have the same biochemical pathway, so researchers could apply such method to these vegetable crops as well.