Vitamin D deficiency is common around the world, with one study suggesting approximately 1 billion people worldwide have vitamin D deficiency, while around 50% of the world population has vitamin D insufficiency. Vitamin D has high physiological importance. A lack of vitamin D can cause bone deformities in children and osteomalacia in adults. A lack of vitamin D has been associated with an increased risk of cardiovascular disease, cognitive impairment in adults, cancer, and several autoimmune diseases.
One of the best-known sources of vitamin D comes from exposure of the skin to sunlight. UVB radiation synthesizes vitamin D from 7-dehydrocholesterol (7-DHC), or provitamin D3 as it is also known; however, individuals who shun the sun or who otherwise have very little exposure to sunlight need to get vitamin D from their diet but most foods contain little or no vitamin D. Good sources of vitamin D are oily fish, red meat, liver, and egg yolks, which poses a problem for vegans. Plants typically have little or no vitamin D, so the vitamin needs to come from fortified foods or supplements.
There could, however, be an alternative. Researchers have used the CRISPR gene editing tool to create biofortified tomatoes, which they claim could provide a new route to vitamin D sufficiency. Tomatoes do produce low levels of provitamin D3, but only in their leaves, which are usually discarded. Provitamin D3 does not accumulate in the fruit, as it is converted as part of cholesterol and steroidal glycoalkaloid (SGA) synthesis. The researchers engineered the plants to accumulate provitamin D3 by turning off an enzyme called Sl7-DR2 enzyme using CRISPR-Cas9. The Sl7-DR2 enzyme normally converts 7-DHC for cholesterol and SGA synthesis.
“Recently it has been shown that a duplicate pathway operates in Solanaceous species, including tomato, where specific isoforms of some enzymes, that are generally responsible for phytosterol and brassinosteroid biosynthesis, produce cholesterol for the formation of SGAs,” explained the researchers. “The existence of a ‘duplicate’ pathway for SGA biosynthesis in tomato makes the engineering of 7-DHC accumulation relatively straightforward.”
The researchers demonstrated their technique resulted in a significant accumulation of provitamin D3 in both the leaves and the fruit, which can be converted to vitamin D3 during exposure to UVB light. After tomatoes were treated with UVB light they were found to contain the same amount of vitamin D as two medium eggs or 28g of tuna, while the leaves of the pant contained up to 600 ug of provitamin D3 per gram of dry weight, which could be converted to vitamin D by shining UVB light on the leaves for 1 hour. Knocking out the enzyme had no effect on plant growth, development, or yield.
In addition to biofortifying tomatoes, the leaves of the fruit could be used for manufacturing vitamin D3 supplements or for fortifying food. It would also be possible to use the same technique in other plants in the nightshade family that share the same biochemical pathway, such as potato, eggplant, and pepper.
You can read more about the study in the paper – Biofortified tomatoes provide a new route to vitamin D sufficiency – which was recently published in Nature Plants. DOI: 10.1038/s41477-022-01154-6