Plants in the nightshade family, known to scientists as Solanaceae, produce a formidable chemical arsenal to defend themselves from pests and disease. These compounds, called steroidal alkaloids, are responsible for the bitter taste that deters predators. For years, a key question has been why different plants, such as tomatoes and eggplants, produce structurally distinct versions of these compounds. New research has uncovered the molecular machinery behind this diversity, revealing an evolutionary story of genetic duplication, adaptation, and even reversal. The findings, published in Nature Communications, highlight how a single enzyme has shaped the chemical defenses across one of the world’s most important plant families.

At the heart of this chemical diversity is a concept known as stereochemistry, which describes the three-dimensional arrangement of atoms in a molecule. Two molecules can be made of the same atoms but exist as mirror images of each other, known as isomers, much like a person’s left and right hands. In nightshades, these alkaloids come in two primary forms: the tomato-type (25S) and the eggplant-type (25R). Scientists discovered that an enzyme from a class known as cytochrome P450 hydroxylases, specifically one named GLYCOALKALOID METABOLISM 8 (GAME8), is responsible for determining which isomer a plant produces. This single enzyme acts as a molecular switch, locking the alkaloid into either its “left-handed” or “right-handed” form.

To understand how this switch evolved, researchers conducted a phylogenetic analysis, essentially building a molecular family tree for the GAME8 gene across dozens of nightshade species. The analysis revealed that the ancestral version of the enzyme likely produced the 25R eggplant-type isomer. Later in the evolutionary history of the Solanum genus, a crucial event called gene duplication occurred, creating a spare copy of the GAME8 gene. This new copy was free to mutate and evolve a new function, eventually giving rise to the 25S-producing enzyme found in modern tomatoes. In some species, such as black nightshade, multiple copies of the GAME8 gene exist, allowing them to produce a mix of both isomers.

Remarkably, the study also found evidence of reverse evolution in action. In wild tomatoes (S. cheesmaniae) from the Galápagos Islands, scientists discovered that mutations in the modern GAME8 enzyme have caused it to revert to producing the ancestral 25R alkaloid. This change suggests that environmental pressures on the islands may favor the ancient chemical defense, driving the plants to re-evolve a trait that was lost millions of years ago. These findings illustrate the complex and dynamic interplay between an enzyme’s function, genetic change, and evolutionary adaptation, providing a clear example of how evolution is not always a one-way street.

References

• Bernstein, J. & University of California- Riverside. (2025, June 24). Tomatoes in the Galápagos are quietly de-evolving. Phys.Org; University of California- Riverside. https://phys.org/news/2025-06-tomatoes-galpagos-quietly-de-evolving.html

• Jozwiak, A., Almaria, M., Cai, J., Panda, S., Price, H., Vunsh, R., Pliner, M., Meir, S., Rogachev, I., & Aharoni, A. (2025). Enzymatic twists evolved stereo-divergent alkaloids in the Solanaceae family. Nature Communications, 16(1), 5341. https://doi.org/10.1038/s41467-025-59290-4