Research: Tomato from Toxin to Table

We love tomatoes, but they weren't always considered safe to eat. Long ago, people in Europe were afraid of them, partly because they didn't understand how lead from old plates could mix with the tomato's acid and make them sick. While Italians recognized its potential as food as early as 1554, it wasn't widely accepted until much later. But the real story of how tomatoes became safe for us to eat is even more fascinating.

Like many plants in the same family, tomatoes make natural poisons called steroidal glycoalkaloids (SGAs). These chemicals, like α-tomatine, protect the plant from bugs and other pests. But they taste bitter and can be bad for us. So, how do tomatoes go from being bitter and potentially harmful to sweet and safe?

The answer lies in how tomatoes ripen. As a tomato changes color and gets softer, it also changes the chemicals inside. The bitter SGAs are turned into a harmless substance called esculeoside A. This change makes the tomato taste good and safe to eat.

Scientists have discovered that this transformation is controlled by the tomato's genes. A special protein called DML2 helps remove certain tags from the tomato's DNA, a process called DNA demethylation. This process turns on genes that change the harmful chemicals into harmless ones.

It's not just one gene doing all the work. The tomato uses a whole team of genes and signals to make this happen. Genes called GAME genes are in charge of making and changing the SGAs. These genes are controlled by signals like ethylene, which helps fruits ripen, and jasmonic acid, which helps plants defend themselves.

Ethylene activates special helpers called transcription factors, like NON-RIPENING, RIPENING INHIBITOR, and FRUITFULL1. These helpers make sure the right GAME genes, like GAME31, GAME40, and GAME5, are turned on at the right time. They also control a transporter gene called GORKY, which helps move the chemicals around. Jasmonic acid activates another helper, MYC2, which controls the GAME36 gene.

All these genes and signals work together to make sure the tomato gets rid of the bitter, harmful chemicals and becomes safe and tasty. This amazing process shows how tomatoes have evolved to protect themselves while also becoming a delicious and important part of our diet.

Reference:
Feng Bai et al., Removal of toxic steroidal glycoalkaloids and bitterness in tomato is controlled by a complex epigenetic and genetic network. Sci. Adv. 11, eads 9601 (2025). DOI:10.1126/sciadv.ads9601

Sources: Science Advances, Futura Sciences