Engineering tomatoes to produce vitamin D

Scientists have used a new way to modify tomato plants to produce fruits rich in a precursor of vitamin D

Scientists have used a new way to modify tomato plants to produce fruits rich in a precursor of vitamin D

Li, J., Scarano, A., Gonzalez, NM et al. Biofortified tomatoes provide a new route to vitamin D adequacy. wet. Plants (2022). https://doi.org/10.1038/s41477-022-01154-6

Reading the pages of the World Sustainable Development Goals 2 (SDG2) – Eradicating Hunger – is depressing to say the least. According to estimates made in 2020, nearly 690 million people, who make up almost 8.9% of the world’s population, will suffer from hunger. This number has increased by 60 million in the past five years. The index, which was initially declining, has been rising since 2015. This doesn’t bode well for SDG2, which has a target of zero hunger by 2030, and the bet is that if this trend continues, the world will have 840 million people. by hunger in 2030.

The ‘invisible’ hunger

Hunger has several consequences, an important part of which is micronutrient malnutrition. This is a term used for diseases caused by a deficiency of vitamins and minerals in the diet. This is a particular problem in developing countries and the number of people suffering from this so-called invisible hunger is staggering. Some methods of combating this include providing micronutrient supplements in the form of tablets or capsules and fortifying food products such as flour or salt by fortifying the micronutrients in them. There is also the route of genetically modifying plants to produce bioenhanced leaves and fruits that can be consumed to alleviate micronutrient hunger.

THE CORE

According to estimates made in 2020, nearly 690 million people, representing almost 8.9% of the world’s population, will suffer from hunger. One of the main reasons for this hunger is micronutrient malnutrition.

A paper in Nature Plants by Jie Li et al attempts to address vitamin D deficiency by genetically modifying tomato plants so that the fruit contains a significant amount of provitamin D3, a precursor from which humans can make vitamin D.

Vitamin D is needed for a process known as calcium homeostasis, which is maintaining a constant concentration of calcium ions in the body.

In this line, a paper in Nature Plants by Jie Li et al attempts to address vitamin D deficiency by genetically modifying tomato plants (Solanum lycopersicum) so that the fruit contains a significant amount of provitamin D 3 which is a precursor from which humans can make vitamin D. Provitamin D 3 has the chemical name 7-dehydrocholesterol, or 7-DHC for short. Humans can synthesize vitamin D from 7-DHC when exposed to ultraviolet B (UVB) light. Vitamin D is needed for a process known as calcium homeostasis, which is maintaining a constant concentration of calcium ions in the body. This is necessary for bone development and strength, among other things, and its deficiency is a cause of conditions such as rickets and osteoporosis.

Other diseases linked to vitamin D deficiency include cancer, Parkinson’s disease, and dementia. Vitamin D 3 is in fish and dairy products. Vegetarian diets are especially deficient in vitamin D.

Mutated tomatoes

The recommended intake of vitamin D is 15 micrograms per day for children and 20 micrograms per day for the elderly. This can be done through supplements or careful exposure to sunlight, but there are several caveats to the latter. It is in this context that the work of J. Li et al. is important. The authors of the article, published in Nature Plants, modified a recently discovered pathway in tomato plants to produce cholesterol and a compound called steroid glycoalkaloid (SGA for short) using the CRISPR-Cas9 gene editing tool. This inhibits the conversion of 7-DHC to cholesterol and instead the former accumulates in the leaves, green and ripe fruits.

Usually, in untreated tomato plants, 7-DHC is present in leaves and to a lesser extent in green fruit, but not in ripe fruit – which is the most consumed of the lot. The researchers showed that in their modified plants, the suppression of the activity of a particular gene “led to substantial increases in 7-DHC levels in leaves and green fruits,” and, according to the paper, while levels of 7-DHC were lower. in the mutant’s ripe fruits, they remained high enough that when converted to vitamin D 3 by shining UVB light, the amount in one tomato would be equal to that in two eggs or 28 grams of tuna, both recommended sources of vitamin D. In addition, the researchers report that the mutants reduced their leaves of a substance called alpha. tomatine, and they note that this may even be beneficial because of the reported toxic or anti-nutritional activity of alpha tomatine. Surprisingly, the cholesterol levels in both fruits and leaves of the mutants were higher than that of the wild-type. This was despite the fact that it had blocked the conversion of 7-DHC to cholesterol.

Need for deeper understanding

Prof PV Shivaprasad, whose group at the National Center of Biological Sciences, Bengaluru, is studying the effect of small RNA biogenesis in establishing epigenetics (epigenetics is the study of how your behavior and environment can cause changes in the way your genes work ), and those not involved in this work notes that while the study opens up a welcome new angle to increasing vitamin D intake, a better understanding is needed. Alpha tomatine is believed to play a role in the plant’s resistance to attacks by viruses, fungi, insects, and herbivores. In addition, it is important for the protection of the plant and its self-preservation, and the reduction of alpha tomatine in the mutants is not necessarily a good thing. The unexplained levels of cholesterol are also surprising and must be explained. So while this experiment is an important one and promises to be fruitful in supplementing vegetarian diets with vitamin D, it needs further investigation and a closer look.

SOURCE – www.thehindu.com

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