The evolutionary ladder is meant to be climbed one rung at a time with an organism shedding some traits and gaining others on the way up. However, in a very surprising twist, some tomatoes on the Galapagos islands are inching back down the ladder.
When they found the backwards-reaching plants, researchers from the University of California, Riverside (UC Riverside), were examining crops on the Galapagos islands in an effort to understand the role alkaloids have in their structure. Crops belonging to the nightshade family like potatoes, eggplants, and tomatoes produce these bitter-tasting molecules to help ward off predation by fungi, insects, and other animals. Too many alkaloids, though, can make the plant toxic to humans.
“Our group has been working hard to characterize the steps involved in alkaloid synthesis, so that we can try and control it,” said Adam Jozwiak, a molecular biochemist at UC Riverside and lead author of the study.
What they stumbled upon was something that challenges the widely accepted belief that, while some organisms may regain old traits through the process of evolution, they don't do it through exactly the same genetic pathways.
They found a batch of tomato plants on the geologically newer western islands of the Galapagos that were pumping out a toxic blend of alkaloids identical to those produced by eggplant relatives that existed millions of years ago. The tomato plants on the older eastern islands, however, were making the same blend of alkaloids found in modern cultivated tomatoes.
Diving deeper, the researchers found that the reason the western plants were pumping out an ancient mix of alkaloids had to do with a change to four amino acids in one of the plants' enzymes. That change, which they feel was likely brought about by the harsher conditions found on the western islands, altered the arrangement of the molecular structure of the alkaloid, making it more toxic.
To test the finding, they induced the same change to tobacco plants, which also did an about-face evolutionarily and started spitting out the old alkaloids.
The team then used DNA from modern day tomato plants to run a modeling experiment to show what it was like before it evolved. Sure enough, when the model ran, it showed that the ancient plants would have been an exact match to the profile of the plants found on today's western Galapagos islands.
While the concept of reverse-evolution is controversial, Jozwiak says their findings indicate exactly that – that the tomatoes have stepped back in time to reproduce the same exact compounds in the same exact way as their ancient relatives did.
“Some people don’t believe in this,” Jozwiak said. “But the genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It happened.”
Jozwiak says the findings could cause scientists to rethink evolution as a more fluid and less linear process and perhaps even entertain the idea that such a process could happen in humans if their environments change sufficiently. He also says that his team's work can open the door to a new type of genetic engineering.
“If you change just a few amino acids, you can get a completely different molecule,” he concluded. “That knowledge could help us engineer new medicines, design better pest resistance, or even make less toxic produce. But first, we have to understand how nature does it. This study is one step toward that.”
The findings have been reported in the journal Nature Communications.
Source: UC Riverside
