Plants that thrive in chemically challenging landscapes appear to be even hardier than researchers had previously thought. A Université de Montréal team supported by Genome Canada examined the molecular response of willow trees living in soil with high levels of petroleum hydrocarbons and found that they expressed a number of key genetic markers differently than willows living in uncontaminated settings. These distinct gene expressions appear to give the trees not just an ability to withstand a polluted environment but also superior biochemical tools for fending off pests.
“In the act of tolerating that nasty environment they have to produce chemicals that allow them to tolerate it,” says Nicholas Brereton, a research associate with the team. “The same chemi-cals that help them fight contamination also have the secondary benefit of giving them protection from attack,” Brereton says.
Brereton co-authored a paper that outlined these findings for willows pot-grown in soil sourced from a former petroleum refinery. Brereton notes that the trees’ genetic sequence was analyzed with de novo transcriptome assembly, a new technique that generates a more complete list of all the proteins present in a biological specimen. Instead of extracting only the plant’s own genetic information, this approach obtains genetic information that the plant has acquired from other organisms it has interacted with, such as fungi, bacteria or insects.
In this case the analysis found that almost half of the genes came from organisms other than the trees. Twenty-four samples were taken from the buds, leaves and stems so there would be no bias in terms of where the RNA was found in the tree. “We looked at everything that was there and we got a much more complex picture,” he says. “We saw a lot of bacteria and fungi that we think are beneficial. We also saw a pest that interacted with the trees.”
That pest, a spider mite that targets willows, accounted for most of these external genes. The unique expression of these genes led the researchers to conclude that the trees in contaminated soil had an advantage when it came to fending off these attackers.
Brereton adds that this observation underscores the importance of analysing complex environmental interactions from the perspective of metaorganisms, a term that refers to the combination of all discrete organisms that might be present rather than one or two. “We didn’t make the assumption that a tree was just a tree,” he says, pointing to the significant number of active genes that would otherwise have been missed. “If you ignore them, you ignore the rest of the story that’s there. It might not be important but it definitely could be.”