Gaby
The berries of the nightshade plant — the ones blamed for killing Roman Emperor Augustus — are infamous for their toxicity. Tomatoes are also members of the nightshade family (Solanaceae) and produce toxic steroidal glycoalkaloids.
So why don’t tomatoes kill us?
Despite their bad reputation—and the cult of John De Bello’s Killer Tomatoes films—tomatoes are harmless.
Though tomatoes (Solanum lycopersicum) were once thought poisonous, they actually convert their bitter toxins into compounds that are palatable and non-lethal. Fen Bai, a biologist at Sichuan University in China, and his colleagues identified the genetic mechanisms behind this safe transformation in tomato fruits.
Nightshades use steroidal glycoalkaloids as a natural defense against pests. These molecules are thought to disrupt animal cell membranes, damaging them and eventually causing cell death.
Potatoes, another member of this toxic family, have been bred to contain safe levels of these compounds, although they can still produce them when damaged or exposed to too much light.
For humans, these glycoalkaloids taste bitter. Eating too much can cause a burning sensation in the mouth, then nausea, cramps, a slowed pulse and breathing, vomiting, diarrhea, internal bleeding, and stomach damage.
However, these plants also need animals to spread their seeds, and animals help with this. So in some species, as fruits ripen the bitter chemicals are transformed into something more palatable.
A team of researchers found that the chemicals that make tomato fruits redder, softer, and sweeter also coordinate the breakdown of the toxic glycoalkaloid into a less toxic compound—esculeoside A.
The authors wrote, “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 plants use epigenetic regulation to make their fruits safe for consumption, Science Alert reported. Specifically, the DML2 protein removes methyl groups, allowing the cellular machinery that reads genes to access the genes involved in blocking toxins.
When researchers genetically disabled DML2 production in tomatoes, the fruits accumulated high levels of steroidal glycoalkaloids.
The team compared the genes involved in related plants and found that DML2-driven DNA demethylation increased during tomato domestication. That change helped tomatoes evolve from small wild berries into the large red fruits we eat today.
At the same time, the expression of genes that support steroidal glycoalkaloid production decreased. Now, even green tomatoes can be safely eaten in moderation.
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.
