New Delhi: Tomatoes can be genetically engineered to produce Vitamin D. This could be a simple and sustainable innovation to address the global health problem of Vitamin D insufficiency, according to a new study.
A team of researchers used gene editing to turn off a specific molecule in the plant's genome which increased provitamin D3 in both the fruit and leaves of tomato plants. The provitamin D3 was then converted to vitamin D3 through exposure to Ultraviolet B (UVB) light. UVB rays are the part of sunlight that gives sunburn.
The study describing gene-edited tomatoes was recently published in the journal Nature Plants.
What Problems Does Vitamin D Insufficiency Cause?
After skin's exposure to UVB light, Vitamin D is created in our bodies. However, the major source of vitamin D is food. The new biofortified crop can help millions of people suffering from Vitamin D insufficiency, a growing issue linked to higher risk of cancer, dementia, and many leading causes of mortality, and also to increased severity of infection by Covid-19.
What Is Provitamin D3?
Provitamin D3 or 7-dehydrocholesterol (7-DHC) is one of the building blocks of vitamin D3. This is naturally present in tomato leaves at very low levels. However, provitamin D3 does not normally accumulate in ripe tomato fruits.
Researchers at John Innes Centre, United Kingdom used CRISPR-Cas9 gene editing to make revisions to the genetic code of tomato plants, in order to ensure that provitamin D3 accumulates in the tomato fruit.
What Is CRISPR-Cas9 Technology?
CRISPR, which stands for Clustered regularly interspaced short palindromic repeats, is the hallmark of a bacterial defence system that forms the basis for CRISPR-Cas9 genome editing technology, and is a highly precise gene-editing tool.
CRISPR-Cas9 edits genes by precisely cutting DNA and then letting natural DNA repair processes take over. CRISPR-Cas9 consists of two parts, namely the Cas9 enzyme and a guide RNA. The system was adapted from a naturally occurring genome editing system that bacteria use as an immune defence.
What Changes Were Observed In The Edited Plants?
According to the study, the leaves of the edited plants contained up to 600 micrograms of provitamin D3 per gram of dry weight. A daily intake of 10 micrograms of Vitamin D is recommended for adults.
When tomatoes are grown, the leaves are usually waste material. However, the leaves of the edited plants can be used for the manufacture of vegan-friendly vitamin D3 supplements, or for food fortification.
How Can Tomatoes Serve As A Sustainable Source Of Vitamin D?
In a statement released by John Innes Centre, Professor Cathie Martin, corresponding author of the study, said the researchers have shown that one can bio-fortify tomatoes with provitamin D3 using gene editing, which means tomatoes could be developed as a plant-based, sustainable source of Vitamin D3.
She added that forty per cent of Europeans have Vitamin D insufficiency, and so do one billion people worldwide. She further said that the researchers are not only addressing a huge health problem, but are helping producers, because tomato leaves which currently go to waste, could be used to make supplements from the gene-edited lines.
Scientists Switched Off A Particular Enzyme In Tomatoes. Know Why
Earlier, scientists have studied the biochemical pathway of how 7-DHC is used in the fruit to make molecules and found that a particular enzyme SI7-DR2 is responsible for converting this into other molecules.
The researchers used CRISPR-Cas9 to take advantage of this. Using the technique, they switched off the SI7-DR2 enzyme in tomato, so that the 7DHC accumulates in the tomato fruit.
The scientists measured how much 7-DHC there was in the leaves and fruits of the edited tomato plants, and observed a substantial increase in levels of 7-DHC in both the leaves and fruit of the edited plants.
According to the study, the 7-DHC accumulates in both the flesh and peel of the tomatoes. Then, the scientists tested whether the 7-DHC in the edited plants could be converted to vitamin D3 by shining UVB light on leaves and sliced fruit for one hour. They observed that the 7-DHC could indeed be converted to vitamin D3 by shining UVB light on the leaves and sliced fruit, and was highly effective.
What Happened After Treatment Of Tomatoes With UV Light?
Following treatment with UVB light to turn the 7-DHC into Vitamin D3, one tomato was found to contain the equivalent levels of vitamin D as two medium sized eggs or 28 grams of tuna. Both these foods are recommended dietary sources of vitamin D.
According to the study, Vitamin D in ripe fruit might be increased further by extended exposure to UVB, for instance, during sun-drying.
The researchers observed that blocking the enzyme in the tomato had no effect on growth, development or yield of the tomato plants. Since other closely related plants such as aubergine, potato, and pepper have the same biochemical pathway, the method could be applied across these vegetable crops.
The UK government announced earlier this month an official review to examine whether food and drink should be fortified with Vitamin D to address inequalities.
Significance Of The Research
Vitamin D is present in little amounts in most foods, especially plants. Vitamin D3, which is the most bioavailable form of Vitamin D, is produced in the body when the skin is exposed to sunlight. People living in higher latitudes need to get Vitamin D from their diet or supplements because the Sun is not strong enough for the body to produce the nutrient naturally. The same is true during winter.
Dr Jie Li, the first author of the study, said that the Covid-19 pandemic has helped to highlight the issue of Vitamin D insufficiency and its impact on people's immune function and general health. She added that provitamin D enriched tomatoes they produced offer a much-needed plant-based source of the sunshine vitamin, which is great news for people adopting a plant-rich, vegetarian or vegan diet, and for the growing number of people worldwide suffering from the problem of Vitamin D insufficiency.