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March 15, 2023

How biofuel crops harness fungal defenders

In a world where switchgrass could cut our fossil fuel dependency, can communities of fungi help grow more potent plants?

Michigan State University researcher Acer VanWallendael understands the public’s fascination with fungus. It is, after all, a fungus that kicks off the zombie apocalypse in the hit HBO series “The Last of Us.”


A microscope image shows the cross section of a plant leaf where its tissue is stained blue. A fungus grows on top of the blue tissue as orange, fan-like structures.
A study on the relationship between plants and fungi (shown in orange) led by Michigan State University researchers was featured on the cover of the journal PLOS Biology. Credit: Raiza J. Castillo Argaez

Thankfully, no known fungus has the power to turn people into monsters and upend society. But VanWallendael, a postdoctoral research associate in the Department of Plant Biology, is helping highlight the very real and diverse ways microscopic fungi affect crops.


More specifically, his team’s recent paper in the journal PLOS Biology explored the complex relationships fungi have with switchgrass, a promising biofuel crop.


“One of the reasons we’re so interested in switchgrass is it’s a perennial crop,” said VanWallendael, who works with the Great Lakes Bioenergy Research Center. “Unlike an annual crop like corn, switchgrass will put down deep roots so it can come back year after year while holding soil in place and storing carbon.


“But one of the downsides is that pathogens can also build up where the grass is growing over time,” he said. “Perenniality might put the plant in conflict with disease.”


In the case of a biofuel candidate like switchgrass, fungal pathogens can both diminish the health of the plant and the quality of fuel made from it, VanWallendael said. At the same time, however, there are fungi that help the plant.


A photo of a dead grasshopper clinging to the top of a grass's flowering stem. The grasshopper is missing part of its abdomen, and dark brown fungal tissue grows at its joints, mouth and cracks in its exoskeleton.
A grasshopper killed by an Entomophaga fungus. Dark brown patches in the cracks in its exoskeleton show fungal spores. Credit: Nate Emery

For example, there are fungi known as hyperparasites that attack fungal pathogens. Others release chemicals that make the grass taste gross to grazing cattle and bison. There are even fungi in the Entomophaga genus that infect grasshoppers that eat the grass.


Like Cordyceps, the fungus featured in “The Last of Us, Entomophaga alters the behavior of its hosts. The infected grasshoppers will stop eating the switchgrass and start basking in the sun to induce a fungus-killing fever. If the fever fails, however, the basking position becomes a perfect launching point for the spores that grow from fuzzy fungal hyphae, or tubular projections, sprouting from cracks in the insect’s carapace.


That’s right. Mind-controlling fungi are real, but don’t worry, they’re working on the side of the plants. And, again, they definitely don’t turn humans into zombies (insects aren’t so lucky, though).


Back on the switchgrass field, thousands of species of microscopic fungi can be present, with hundreds on a single switchgrass leaf that change over time. On top of that, the Great Lakes Bioenergy Research Center is studying several different varieties of switchgrass.


VanWallendael and his colleagues are showing which combinations result in the most robust, resilient grass as well as how plants with certain gene variants can control the fungi colonizing them. The team is looking to provide information that will help researchers grow the healthiest switchgrass for biofuel and help remediate damaging fungal infections.


An illustration shows the ranging roles fungi can have for switchgrass. A bison stands next to a patch of switchgrass on the left with text reading, “herbivore deterrence.” An inset on the right shows a magnified view of the grass with a grasshopper resting on a blade. Text outlines several other relationships between the fungi and plant. Beneficial relationships include herbivore infection — shown on the grasshopper, which is covered in fuzzy white patches — nutrient uptake, hyperparasitism and immune priming. The neutral roles are decomposers and detritivores, and the negative role is pathogens.
Michigan State University researchers are highlighting the diverse roles of microbial fungi in the overall health of switchgrass, a promising biofuel crop. Credit: Chelsea Mamott

They also hope their work will help remind folks that these fungi play an outsize part in shaping our world, even if it isn’t quite as dramatic as we see on TV.


“It’s easy to forget about microscopic fungi. There’s the yeast in our bread and in our beer, but we tend to ignore them in the wild,” VanWallendael said. “I hope this helps people remember that there are whole communities of fungi in a single leaf doing really interesting things that are important to the success and failure of the plant.”


VanWallendael is a postdoctoral researcher in the lab of David Lowry, an associate professor in the College of Natural Science. The team’s work was also supported by the National Science Foundation Long-term Ecological Research Program at the W.K. Kellogg Biological Station and by Michigan State University AgBioResearch.

By: Matt Davenport and May Napora