GabyThe berries of the nightshade plant, which are believed to have killed Roman Emperor Augustus, have a reputation for being deadly. Like those berries, tomatoes belong to the nightshade family (Solanaceae) and make steroidal glycoalkaloids, compounds that can be toxic. So why don’t tomatoes pose a threat to us? Despite their sinister reputation—partly thanks to director John De Bello’s films about killer tomatoes—these fruits are harmless. Once thought poisonous, tomatoes actually convert their bitter toxins into harmless, tasty compounds. Fen Bai, a biologist at Sichuan University in China, and his colleagues have identified the genetic mechanisms behind that safe transformation.
Nightshades use steroidal glycoalkaloids as a built-in defense against pests. These molecules can disrupt animal cell membranes, damaging them and sometimes causing cell death. Potatoes, another nightshade relative, are typically bred to keep these compounds at safe levels, though damaged or sun-exposed potatoes can still produce them. For humans, glycoalkaloids taste bitter and, in large amounts, can cause a burning mouth, nausea, cramps, slowed pulse and breathing, vomiting, diarrhea, internal bleeding, and stomach damage. But plants need animals to eat their ripe fruit and disperse seeds, so some species convert bitter toxins into more palatable chemicals as the fruit matures.
A research team found that the same chemical changes that make tomatoes redder, softer, and sweeter also drive the breakdown of the toxic glycoalkaloid into a less toxic molecule called esculeoside A. The paper put it this way: “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.”
Tomatoes use epigenetic regulation to make their fruits safe to eat, Science Alert reported. Specifically, the DML2 protein removes methyl groups from DNA, opening up genes that promote the conversion of toxins. When researchers genetically disabled DML2 in tomato plants, the plants produced fruits with high levels of steroidal glycoalkaloids. Comparing related species, the team found that DML2-driven DNA demethylation increased during tomato domestication, a change that helped the plants develop from small wild berries into the larger red fruits we eat today. At the same time, the activity of genes that support glycoalkaloid production declined. Now, even green tomatoes are safe to eat in moderation. The outcome: humanity gained a delicious crop that doesn’t kill and even offers health benefits. The study was published in Science Advances.
