GM tomatoes: Engineering tomatoes to produce vitamin D

What is the News?

A paper in Nature Plants tries to address vitamin D deficiency by genetically modifying tomato (Solanum lycopersicum) plants so that the fruit contains a significant amount of provitamin D3 which is a precursor from which humans can make vitamin D.

What is the need for GM Tomatoes?

The term ‘invisible’ hunger is used for diseases caused by a deficiency of vitamins and minerals in the diet. This is a major problem in developing countries. Hence, genetically modifying plants to produce biofortified leaves and fruit is one of the solutions to address the hidden hunger.

About vitamin D

Provitamin D3 is a precursor from which humans can make vitamin D. The chemical name of Provitamin D3 is 7-dehydrocholesterol, or 7-DHC. Humans can synthesise vitamin D from 7-DHC when they are exposed to ultraviolet B (UVB) light.

Vitamin D3 is also present in fish and dairy products.

Functions of Vitamin D: It is needed for a process known as calcium homeostasis which is the maintenance of a constant concentration of calcium ions in the body.

Hence, vitamin D is needed primarily for bone development and strength.

Recommended intake: 15 micrograms per day for children and 20 micrograms per day for elders. This can be given through supplements or a careful exposure to sunlight.

But vegetarian diets are particularly deficient in Vitamin D.

Deficiency: Vitamin D deficiency can cause conditions such as rickets and osteoporosis. Other diseases that are associated with vitamin D deficiency are cancer, Parkinson’s disease and dementia.

Why tomatoes are chosen, and how did GM tomatoes address vitamin D deficiency?

In untreated tomato plants, 7-DHC is present in leaves and to a lower extent in green fruit, but not in ripe fruit. This is because 7-DHC is converted into cholesterol in fruit.

Recently, a scientist discovered a pathway in tomato plants to produce cholesterol and a substance called steroidal glycoalkaloid (SGA for short) using the CRISPR-Cas9 gene editing tool. This inhibits the conversion of 7-DHC to cholesterol.

The researchers showed that in their modified plants there is a “substantial increase of 7-DHC levels in leaves and green fruit,” but levels of 7-DHC were lower in ripe fruits of the mutant.

However, the amount in one tomato would be equivalent to that in two eggs or 28 grams of tuna, both of which are recommended sources of vitamin D.

What are the concerns associated with GM tomatoes?

Reduction in Alpha-tomatine: Alpha-tomatine is reported toxicant or antinutritional activity. The researchers report that the mutant tomatoes showed a reduction of alpha-tomatine in their leaves.

Alpha-tomatine is believed to have a role in the plant’s resistance to viral, fungal, insect and herbivoral attacks. Hence, the reduction of alpha-tomatine in the mutants may not necessarily be a good thing.

High levels of cholesterol: Despite blocking the conversion of 7-DHC to cholesterol, the cholesterol levels in both fruit and leaves of the mutants were higher than of the wild-type. This need to be studied further.

Source: The post is based on the article “Engineering tomatoes to produce vitamin D” published in The Hindu on 24th May 2022.

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