Researchers at the University of Kentucky Martin-Gatton College of Agriculture, Food and Environment (CAFE) have discovered that a fungus living inside a common Kentucky woodland grass produces a rare combination of chemicals that likely helps protect the plant from hungry insects.
Published in Applied and Environmental Microbiology, the study looked at bearded shorthusk, a wild grass that grows in forests across the Commonwealth. Inside this grass is the fungus Epichloë brachyelytri, an "endophyte" that lives inside a plant without harming it. In fact, the fungus and the grass are symbiotic-the grass gives the fungus a home, and in return the fungus makes chemicals that keep bugs from eating the plant.
The research team, led by Christopher Schardl, Ph.D., and Padmaja Nagabhyru, Ph.D., in the Department of Plant Pathology, found that this fungus makes three different alkaloids. Two of them-exo-1-acetamidopyrrolizidine and chanoclavine-are usually just middle steps that other fungi turn into more complex chemicals. But this fungus stops the process early and keeps them as the final product.
"What makes it special is that it is the first fungus ever shown to do this with both chemicals at the same time," Schardl said.
The team collected grass samples from six different locations across Kentucky, stretching along a 171-kilometer path. Among these locations were the Kentucky River Palisades, Mammoth Cave National Park, Red River Gorge and Carter Caves State Resort Park. They also studied grass grown at The Arboretum, State Botanical Garden of Kentucky, where UK staff members Wes Hansen and Judson Collins helped grow the plants.
With an ultrahigh-performance liquid chromatography (UHPLC)-Tandem Mass Spectrometry (MS/MS) machine, an instrument used to measure tiny amounts of chemicals in each grass sample, the scientists were able to compare how much of each alkaloid was in leaves, seeds and young shoots.
Making these chemicals costs the fungus a lot of energy, according to study author Schardl.
"We have intriguing evidence that in young shoots, the endophyte has an internal struggle over which chemical pathways to feed, when those pathways need the same building blocks," said Schardl. "That also explains why the endophyte has lost one or another of these chemicals in a few locations where we guess that insects aren't as much of a problem and the fungus can save energy by skipping some of the chemistry."
This suggests that producing these bug-fighting chemicals is a big investment for the fungus, so that in most places they must be important for survival.
The team also found that the rare chemical combo discovered in this forest grass originated in other fungus species through different evolutionary paths-including gene-swapping between species and hybridization when two species mix.
Understanding how these grass-fungus partnerships work matters beyond just forest ecology. Similar fungi live inside pasture grasses that cattle and horses eat, and some of those fungi make chemicals that can be toxic to livestock.
"Finding it more often than expected by chance motivated us to investigate if this chemical blend is an especially potent protectant from insects," Schardl said. "Studying wild examples like this helps scientists understand how the whole system evolved and how they might use it to breed better, safer pasture grasses in the future."
Learn more about the Department of Plant Pathology at Martin-Gatton CAFE at plantpathology.mgcafe.uky.edu.
Research reported in this publication was supported by the U.S. National Science Foundation under Award No. 2030225. The opinions, findings, and conclusions or recommendations expressed are those of the author(s) and do not necessarily reflect the views of the U.S. National Science Foundation.
This material is based upon work supported by the Agricultural Research Service, U.S. Department of Agriculture, under Agreement No. 59-5042-5-003, and the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2026-67039-46777. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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