Scientists at the John Innes Center in the UK have used the Crispr/Cas9 genetic engineering technique to modify tomatoes in such a way that they enrich the fruit and leaves with vitamin D. The first field trials will start in June. If the British relax the rules for new genetic engineering as planned, the tomatoes could soon be on the market. Critics of genetic engineering doubt that they can really provide people with vitamin D.
Tomatoes naturally contain very small amounts of 7-dehydrocholesterol. The substance is also called provitamin D3 because vitamin D3 develops from it when exposed to ultraviolet light. While researching the metabolic processes in the tomato, scientists discovered that an enzyme converts 7-dehydrocholesterol into other plant substances, the esculeosides. They help the tomato fight off pests and pathogens. The team at the John Innes Center (JIC), led by Professor Cathie Martin, has now used Crispr/Cas9 to silence the gene that produces this enzyme. As a result, the 7-dehydrocholesterol accumulated in the leaves and fruits of the manipulated tomato plants – while the content of esculeosides decreased significantly.
If the tomatoes modified in this way were irradiated with UV light (which the sun has to do outdoors), the 7-dehydrocholesterol in the fruit was converted into vitamin D3. In a study published in the journal Nature Plants, the JIC researchers calculated that one would consume just as much vitamin D with such a tomato as with the consumption of two eggs or 28 grams of tuna. In addition, the vitamin D3 in the leaves could be processed into dietary supplements. The tomato is therefore suitable for compensating for a poor supply of vitamin D, which, according to the study, affects one billion people. Other closely related plants that share the same metabolic pathway, such as aubergines, potatoes and peppers, could also be made to accumulate vitamin D using this method, the JIC press release said. Especially during the corona pandemic, it became clear how important a good vitamin D level is for health.
Switching off the gene did not have a negative effect on the growth, development and yield of the plants, according to the study experience in the greenhouse. It remains to be seen whether this also applies to the field. The Munich Institute Testbiotech warns that the genetic engineering intervention in their protective mechanism could make the tomato more susceptible to disease and pest infestation. Other interactions with the environment would also have to be investigated. In the case of the tomatoes themselves, it should be checked whether the intervention has unintentionally changed ingredients or disrupted other metabolic pathways. Finally, Testbiotech points out that the vitamin D concentration in tomatoes can vary greatly depending on the variety and environmental conditions. In the journal Nature, scientists comment that more research needs to be done on how stable the vitamin in the tomato is when it is stored or processed. It also needs to be clarified how well the human body can absorb the vitamin from the tomatoes. It is impossible to dose reliably in this way, writes Testbiotech.
In order to identify possible risks to health or the environment at an early stage, the institute calls for the risks of these genome-edited plants to be examined in detail. Liz O’Neill, CEO of anti-GMO organization GM Freeze, says the new tomato is simply superfluous: “Supermarket shelves are already full of excellent sources of vitamin D: from oily fish, eggs and red meat to fortified cereals and a range of dietary supplements”. Adding an “obscure tomato” won’t solve the problem of vitamin D deficiency because poor nutrition is a consequence of poverty and a broken food system. “We need systemic change, not genetically engineered ketchup,” O’Neill said. [lf/vef]