Chemical Analysis Can Help Scientists Decode the Tree of Life

If you’ve ever stepped in poison ivy, you likely know what’s coming next: an itchy blistering red rash wherever the leaves made contact with your skin. But it’s not the leaves themselves that are the problem. It’s the oily chemical coating the leaves, urushiol, that makes your ankles beg for ointment.

Urushiol is just one of countless chemicals produced by plants, either for development, growth, reproduction, or defense. Urushiol makes itself painfully known, but most chemicals produced by plants are difficult to detect. Though scientists can sequence a plant’s entire genetic code, they still may have no idea what chemicals a plant actually produces.

A plant in the genus Espeletia, commonly known as frailejón or fraylejón

“We have to look at chemistry as another important source of information, and integrate it with biology,” said Guillermo F. Padilla-Gonzalez, a researcher at the University of Sao Paulo, Brazil. Researchers are now looking to layer chemical evolution over the history DNA has given them for a more complete view of how ecosystems developed.

Padilla-Gonzalez lead a study, which was published in Scientific Reports in August, that used chemical analysis to complement the genetic tree of the Espeletia genus, a group of perennial shrubs. This type of chemical analysis is called metabolomics, “the study of the whole set of chemicals produced by an organism,” Padilla-Gonzalez said.

Padilla-Gonzalez and his team decided to study Espeletia because it is an important part of its ecosystem, is abundant, and, most importantly, members of the genus were relatively recently separated from each other by the formation of valleys, allowing new species to form.

Most of the compounds examined in the study were found in all of the samples, but some were specific to certain regions. “The most likely explanation is that because of this isolation by distance, species growing in these areas found unique ways for adapting to their environments,” said Mauricio Diazgranados, a lead researcher at the Royal Botanic Gardens and an author of the study.

This study was the first time a research team was able to use metabolomics to map how species diverge over time, and that was largely because of recent advances that make analysis much faster.

In the past when researchers wanted to look at the metabolites of plants they would have to go through a difficult and time consuming process. “It used to take a lot of time and effort to isolate one single chemical to identify it from a single plant,” Padilla-Gonzalez said.

Now it is unnecessary for researchers to isolate the compounds, allowing them to examine many chemicals from many different plants, and compare them. “When you use these kinds of techniques you can analyze hundreds of plants in just a few days,” Padilla-Gonzalez said.

These advances allowed Padilla-Gonzalez and Diazgranados to analyze the leaves of 120 plants from the genus, Espeletia. Whereas analyzing this number of plants would have been impossible due to time and budget constraints before, now it represents a manageable task.

“The thing that’s really challenging about plant metabolites is that they’re immensely diverse, and they’re also rare,” said Brian Sedio, a postdoctoral fellow at the Smithsonian Tropical Research Institute. While each plant contains thousands of different metabolites, they’re often specific to the plant or its environment, making finding a specific chemical difficult.

Now that researchers don’t have to isolate specific chemicals, these challenges are less daunting. They don’t have to know exactly what they’re looking for, in order to find it. Researchers are able to look at every metabolite a plant produces, allowing them to find chemicals they didn’t know existed before.

By comparing a new chemical with a database of known chemicals, “you can identify what’s in there, and therefore also identify what isn’t known,” Sedio said. Meaning, researchers are now able to rapidly identify how many chemicals they’re analyzing are previously unknown molecules.

In Padilla-Gonzalez and Diazgranados’ study, they were able to identify 46 compounds, 19 of which were previously unreported in the subtribe, and 21 of which were unreported in the genus. Not only is metabolomics giving researchers a more nuanced view of plants’ evolutionary history, it’s also allowing them to discover new and unique metabolites.

“We expect to find new chemical compounds when we expand the study to the other genera and the other species, and that just tells you how little we know of the chemistry of most of the plant species in the world,” Diazgranados said.