Tomatoes don't actually kill people: why scientists had to prove this (video).

According to one theory, the berries of the nightshade that killed the Roman Emperor Augustus are infamously known for their lethality. Interestingly, tomatoes (Solanum lycopersicum) belong to the same plant family, the nightshades, and also produce toxic steroidal glycoalkaloids — as a result, they were considered poisonous for a long time, writes Science Alert.

Fortunately for us, tomatoes do not actually kill people: they transform their bitter toxins into something more palatable and less deadly. According to co-author of the study, biologist Feng Bai from Sichuan University, he and his colleagues were able to identify the genetic mechanisms involved in the safe transformation of tomato fruits.

Nightshades utilize steroidal glycoalkaloids as a natural defense against pests. It is believed that these molecules interfere with the membranes of animal cells, damaging them and ultimately causing cell death.

Another member of this toxic family is the potato — it has been cultivated with a safe level of these compounds, although it can also produce them when damaged or exposed to excessive light.

Researchers found that for humans, this glycoalkaloid substance is unpleasantly bitter in taste, and consuming too much of it leads to a burning sensation in the mouth, followed by symptoms such as:

• nausea;
• cramps;
• slowed pulse;
• slowed breathing;
• vomiting;
• diarrhea;
• internal bleeding;
• stomach damage.

At the same time, plants need their seeds to be dispersed, and animals help with this. Therefore, in some plants, as their fruits with seeds ripen, the bitter toxic chemicals are transformed into something more pleasant in taste.

In a new study, the results of which were published in the journal Science Advances, Bai and colleagues discovered that in tomatoes, these chemicals make the fruits redder, softer, and sweeter, as well as coordinate the breakdown of the toxic glycoalkaloid into a less toxic compound called esculeoside A. This ensures low levels of toxic steroidal glycoalkaloids, allowing for resistance to herbivore attacks and ensuring that the fruits reach seed maturity.

A protein called DML2 allows the cellular genetic machinery to access the genes involved in stopping toxins by removing methyl groups. In the course of the study, the scientists genetically disabled the production of DML2 in tomatoes and found that the resulting fruits still contained high levels of steroidal glycoalkaloids.

Next, the researchers compared the genes involved in other related plants. The results suggest that the demethylation of DNA under the influence of DML2 increased during the domestication of the tomato, which transformed the plants from producers of small berries to creators of large red fruits. Meanwhile, the levels of genes supporting steroidal glycoalkaloids also decreased — in simple terms, this allows for the safe consumption of even green tomatoes.