GabyThe berries of the nightshade plant, which are believed to have killed Roman Emperor Augustus, are infamously known for their deadly nature. Like these berries, tomatoes also belong to the nightshade family (Solanaceae) and produce toxic steroidal glycoalkaloids. But why don’t tomatoes pose a threat to us? Despite their notorious reputation, largely thanks to director John De Bello’s films about killer tomatoes, these vegetables are harmless. While tomatoes (Solanum lycopersicum) were once thought to be poisonous, they actually transform their bitter toxins into something tasty and non-lethal. Fen Bai, a biologist from Sichuan University in China, and his colleagues have identified the genetic mechanisms involved in the safe transformation of tomato fruits.
Nightshades use steroidal glycoalkaloids as a natural defense against pests. These molecules are believed to interfere with animal cell membranes, damaging them and ultimately leading to cell death. Potatoes, another member of this toxic family, have been cultivated with safe levels of these compounds, although they can also produce them when damaged or exposed to excessive light. For humans, this glycoalkaloid compound tastes unpleasantly bitter. Consuming too much can lead to a burning sensation in the mouth, followed by symptoms such as nausea, cramps, slowed pulse and breathing, vomiting, diarrhea, internal bleeding, and stomach damage. However, these plants also need to spread their seeds, and animals help with this. Therefore, in some plants, as their fruits mature, the bitter toxic chemicals are transformed into something more palatable.
A team of researchers discovered that the chemicals responsible for making tomatoes redder, softer, and sweeter also coordinate the breakdown of the toxic glycoalkaloid into a less toxic compound—esculeoside A. As the scientists explained in their report, “high levels of toxic steroidal glycoalkaloids are retained in unripe fruits, protecting them from herbivore attacks and ensuring that the fruits reach the seed maturation stage.”
These remarkable vegetables utilize epigenetic regulation necessary to make their fruits safe for consumption, as reported by Science Alert. Specifically, the DML2 protein enables the cellular gene-reading mechanism to access genes involved in blocking toxins by removing methyl groups. When researchers genetically disabled the production of DML2 in tomatoes, they obtained fruits that contained high levels of steroidal glycoalkaloids. The team compared the genes involved in other related plants and found that the DNA demethylation caused by DML2 increased during the domestication of tomatoes. This allowed the plants to evolve from small berries into large red fruits. Meanwhile, the levels of genes supporting steroidal glycoalkaloids also decreased. Now, even green tomatoes can be safely consumed in moderate amounts. Ultimately, humanity has gained a delicious crop that not only doesn’t kill but also offers numerous health benefits. The results of the study were published in the journal Science Advances.
