Genetically modified tomatoes are a source of vitamin D – PCR News

More than one billion people worldwide are deficient in vitamin D, which leads to impaired skeletal development, an increased risk of cancer, neurodegenerative and infectious diseases. Vitamin D can be synthesized in the human body by exposure to medium wavelength B (UVB) light from the precursor 7-dehydrocholesterol (7-DHC, provitamin D3), but its main source remains food of animal origin. An international team of scientists led by Professor Cathy Martin of the John Innes Center in the United Kingdom has created a range of tomatoes that can serve as a plant source of vitamin D.

Some plants have provitamin D.3 serves as an intermediate in the biosynthesis of cholesterol and steroid glycoalkaloids – compounds that play protective functions in plants. In tomatoes, 7-DHC has been found in the leaves. in immature fruits it is rapidly converted to tomato alkaloids and when ripe to squash. Other important plant steroid compounds are the phytohormones brassosteroids, which regulate their growth and development. In the evening primrose family, to which tomatoes belong, there was a doubling of the genes of steroid metabolism, which separated the enzymes for the biosynthesis of steroid alkaloids and phytohormones. Thanks to this, scientists were able to genetically intervene in these metabolic pathways and artificially stimulate the accumulation of provitamin D.3 in fruit without affecting plant growth.

A specific isoform of the enzyme 7-dehydrocholesterol reductase, Sl7-DR2, is responsible for converting 7-DHC to cholesterol and then to alpha-tomato. It is reasonable to assume that suppression of the activity of this enzyme gene will lead to the accumulation of 7-DHC in fruit. To do this, the researchers used the CRISPR-Cas9 system. They generated two complementary RNA strands to the second exon of the gene and received homozygous mutants in the second generation with loss of enzyme function but do not carry the Cas9 gene (this is necessary to avoid subsequent genomic rearrangements).

As expected, the mutants did not show growth or developmental disorders, as the mutation did not affect the biosynthesis of brassosteroids. Provitamin D level3 in leaves and immature fruits was significantly higher than in wild plants.

In ripe fruits, the level of provitamin decreased. However, there was as much 7-DHC left in a ripe tomato as in 28 grams of tuna or two medium-sized chicken eggs (if you convert provitamin to vitamin D3).

The authors evaluated the levels of steroid metabolites in fetal tissues using matrix-assisted laser desorption / ionization imaging (MALDI imaging). The level of 7-DHC increased in both the pulp and the skin of the fruit. Levels of alpha-tomato and scleoside A have been reduced, which may improve the nutritional quality of the fruit, as tomatoes are toxic. However, the mutation also increased the cholesterol content of fruits and leaves.

The first step in converting provitamin D3 a biologically active vitamin D requires exposure to ultraviolet light. Scientists have shown that UV treatment of genetically modified tomato leaves and fruits caused conversion and the vitamin content in one fruit was 20-30% of the daily value (2.8 micrograms per day in the UK and 4.3 micrograms per day in the UK). USA).

Double pathways for steroid biosynthesis exist in other cultivated plants of the nocturnal family – potatoes, eggplants, peppers. Since peppers can be consumed green, and the accumulation of provitamin D3 was higher in immature photosynthetic tomato fruits, perhaps this crop is more promising as a source of the vitamin. In addition, there are mutations that increase the penetrating power of ultraviolet radiation in the tissues of the fetus. Thus, in pink tomatoes, the synthesis of yellow chalcone pigments in the skin is disturbed, which usually absorb ultraviolet radiation. The green stem parts of the plants can also be used as a raw material for the production of the vitamin.

Similar work was done almost simultaneously
Done scientists from South Korea. They confirmed that in plants containing only a common biosynthetic phytosteroid pathway (such as Arabidopsis and lettuce), a reduction in the regulation of the 7-dehydrocholesterol reductase gene leads to dwarfism and growth failure. In tomatoes, however, the treatment did not affect growth and allowed the daily requirement of vitamin D to be met in a single tomato.

Increase in Provitamin D3 demonstrates the great potential of biotechnology in creating a healthy plant-based diet. However, more research is needed on the metabolic pathways of tomatoes, the protective function of alkaloids for plants and the relationship between tomato tolerance to environmental change.

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