The Galapagos Islands They are the living laboratory of evolution. It was there that Charles Darwin observed the differences in finches that cemented his famous theory of natural selection and that laid new foundations for the evolution of the human species. Now, almost 200 years later, these islands are back in the news, but for a surprising reason: a species of wild tomato seems to be turning the evolutionary clock.
But the most important thing of all is that this involution in vegetation opens the door for us to understand how small changes can give us a wide range of possibilities in human pharmacology.
The discovery. A new study published in Nature Communications has discovered that, while evolution followed its “normal” course on the oldest islands of the archipelago, the tomatoes on the younger, more hostile islands have “devolved.” And they are actively recovering a chemical trait that their ancestors lost millions of years ago, something that doesn’t seem too logical.
And it is not logical because we all have in mind that changes are always for the better to adapt to a specific environment. But these plants are giving us a completely different perspective than what Darwin saidalthough it has important applications especially in pharmacology.
A chemical twist. The study of ‘involution’ focuses on the steroidal alkaloids (SGAs), powerful compounds that plants of the Solanaceae family (such as tomatoes, potatoes and eggplants) use as a natural defense. These compounds have a key characteristic: chirality.
This means that a molecule can exist in two forms which are mirror images each other, as if it were our left and right hand, or even a reflection of ourselves in a mirror. The two ways are the following:
- The modern “tomato type”: mainly produces the 25S isomer.
- The ancestral “eggplant type”: produces the 25R isomer.
In this way, the study is seeing that although years ago it was normal to produce 25R, it was later changed to producing 25S. Now, evolution is taking off again to return to the most ancient.
Behind this is an enzyme called GAME8 that has dictated what type of chemical defense each plant produces. In fact, the researchers showed that by modifying just eight amino acids of the tomato GAME8 enzyme, they could stop it from producing its 25S compound and make exclusively the ancestral 25R. It is literally an evolutionary switch.
Evolution in ‘reverse’. This is where the plot thickens. The researchers analyzed the Solanum cheesmaniaea wild tomato endemic to the Galapagos. And what they found challenges the idea of linear evolution:
- On older islands, such as St. Kitts, tomatoes almost exclusively produce the ‘modern’ 25S isomer.
- On more modern islands like Isabela, tomatoes have changed and accumulate high levels of the ‘ancestral’ 25R isomer.
It’s not that these plants were “left behind.” The data suggest that their immediate ancestors produced 25S, but the unique environmental pressures of younger islands have favored mutations in their enzyme. GAME8 that they have made it return to produce the ancestral compound 25R. It is a clear case of reverse evolution.
Because. Younger islands are more arid and hostile environments, and science suggests that this ‘ancient’ chemical cocktail could offer better protection against pathogens or herbivores specific to that inhospitable environment, or even help the plant in different soil conditions.
The important thing. Beyond being a botanical curiosity, chirality is a fundamental concept in pharmacy. One isomer of a drug may be therapeutic, while its mirror ‘twin’ may be harmless or, in infamous cases such as thalidomide, tragically toxic.
Understanding how nature has managed to make a single enzyme (GAME8) change its product from 25S to 25R through a few mutations is a great advance for biotechnology. We could, in theory, use this knowledge to engineer crops with specific alkaloid profiles, creating more resistant plants or, conversely, eliminating anti-nutritional compounds.
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