Scientists have discovered a mechanism that transforms toxins into pleasant-tasting substances in tomatoes.

Modern tomatoes belong to the nightshade family, which means that in the distant past, they were much more dangerous than they are today. The fruits of nightshades are often toxic, although there are exceptions: the fruits of peppers, ground cherries, and eggplants are edible. The fruits of potatoes are poisonous, just like those of deadly nightshade, belladonna, and Jimsonweed, but the tubers, which are the underground part of the plant, are safe to eat.

Most members of the nightshade family become less toxic as they ripen, allowing animals to eat them and spread their seeds to new areas. However, the process underlying this phenomenon is not well understood.

This time, the research team focused on modern tomatoes. In their early developmental stages, they are not toxic, but they are also not very palatable, as they still produce a certain amount of toxic compounds—steroidal glycoalkaloids. The scientists selected tomatoes among other nightshades because humanity has conducted extensive genetic research on them, which provides reliable data.

To understand the natural process of transformation in tomatoes, the researchers examined databases for potential genetic clues. They found evidence that the same chemicals involved in the ripening of tomatoes facilitate the breakdown of glycoalkaloids into esculeoside A—a less toxic compound. These substances turned out to be proteins.

To determine the role that proteins play in the transformation process, the researchers created genetically modified plants in which they could turn the production of these proteins on and off. This allowed the scientists to observe the effects of each substance.

The researchers discovered a protein called DML2 that prevents the breakdown of glycoalkaloids. When the production of this protein was turned off, the tomatoes became too bitter. Further investigation revealed that this protein is capable of breaking down glycoalkaloids through a chemical process known as demethylation. The scientific work has been published in the journal Science Advances.

By analyzing data from previous studies, the team found that as tomatoes were domesticated over the past few centuries, demethylation increased, leading to the development of increasingly sweeter fruits.