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ORNL: Tomás Rush: Decoding the secret language of plants and fungi

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Tomás Rush began studying the mysteries of fungi in fifth grade and spent his college intern days tromping through forests, swamps and agricultural lands searching for signs of fungal plant pathogens causing disease on host plants.

Today, as a plant pathologist and mycologist at Oak Ridge National Laboratory, he’s using his knowledge to better understand the symbiosis between plants and fungi with the goal of creating hardier bioenergy and food crops.

Rush is particularly interested in the chemical signaling that affects the symbiosis between fungi and plant roots. The resulting fungal network extends far from its plant host to increase nutrient uptake and provide a warning system against disease and pests. In return, plants feed carbon to the fungus, which encourages its growth. An estimated 90% of land plants have mycorrhizal fungi associated with their roots.

While a doctoral student at the University of Wisconsin–Madison, Rush embarked on a study that found that certain signaling molecules thought to be produced by a limited number of microbes were actually transmitted by a majority of fungal species. These signals, known as lipo-chitooligosaccharides, or LCOs, likely govern the colonization of plant roots by fungus and may be involved in other important processes as well.

“We found that this signal is produced by most organisms throughout the fungal kingdom,” Rush said. “The discovery resulted in a paradigm shift in our thinking about how these organisms communicate.”

As part of the Plant Microbe Interfaces Scientific Focus Area at ORNL, Rush is exploring how LCOs influence the plant microbiome. “Just as we discovered how important gut flora is to human health, we’re working to understand how this communication between plants, fungi and bacteria affects the well-being of plants,” he said.

One of Rush’s research areas is focused on the presence of LCO receptors in many types of plants, in fungi, and even in humans. A previous study showed that endothelial cells in rat aorta assays have been shown to respond to the signal, “so there may be a larger role for LCOs in mammalian processes than we currently know,” he said.

Rush and colleagues published a paper suggesting LCOs may have a function in the growth and development of the Laccaria bicolor fungus typically associated with the poplar tree, a key bioenergy crop. Their ongoing work examines how the influence of LCOs may be changing the metabolic profile of the fungus that helps poplar grow.

Coming around to plant pathology

Botany was a familiar subject throughout Rush’s childhood. His father, Milton Charles “Chuck” Rush, was a plant pathologist focused on disease-resistant rice crops at Louisiana State University, where he bred a commercially successful rice hybrid named Blanca Isabel after Tomás’ mother.

Tomás said his father, now deceased, would have gotten a kick out of his career trajectory. “I always said as a kid that I didn’t want to be a plant pathologist. And now it’s my passion.”

“Being in the lab was second nature to me growing up,” he added, as his father encouraged his scientific observations. From fifth grade through high school, Tomás collected and experimented on fungi in science fair projects. He went on to earn a bachelor’s degree in biological and agricultural engineering at LSU but later decided that an engineering career wasn’t the right fit.

Rush earned a master’s degree in plant health at LSU, where advisor Catherine Aime, now at Purdue University, again piqued his interest in fungi. “Dr. Aime really inspired me,” Rush said. “She traveled the world collecting new species of fungi.”

Rush expanded his knowledge and interest in fungal symbiosis and metabolism in the labs of Jean-Michel Ané and Nancy Keller at UW–Madison. Rush specialized in applied plant pathology and the elucidation and characterization of fungal metabolites as he earned his doctorate. After graduation, he faced what he thought were limited choices for research in academia or industry.

“It was then that I met ORNL scientist Jesse Labbé at a conference and heard about national lab research for the first time,” Rush said. “I decided it was right up my alley; exactly where I wanted to be.” He came aboard as a postdoctoral researcher at ORNL in October 2019 and was hired as a staff scientist two years later.

“I love the work I do and the people I work with,” Rush said. “It’s a cliché, but this is my dream job that I never knew existed.”

“I tend to think outside the box, and at ORNL we’re always looking for new approaches,” he said. Rush started working in LCO signaling at the lab, and that has expanded to metabolites, lipids and different plant pathogens that affect poplar trees and how to mitigate those diseases. “We also look at development of new products to apply to crops to boost plant health and biomass.

“The science we’re conducting at ORNL could serve as a model to combat other diseases. That’s super exciting.”

Opening a scientific treasure chest

His biggest success? Rush points to the ORNL science culture. “You get an idea, people get very interested in it, so you go talk with colleagues in the analytical chemistry group, then you go to the computational group, and then the imaging group. Success is having all these collaborators get excited about a question and then help answer it.”

Down the road, Rush said he is eager to try more outside-the-box ideas such as using artificial intelligence and high-performance computing to detect fungal pathogens and discover metabolites faster in collaboration with other scientists at ORNL.

“There’s still a lot to learn in mycology,” Rush said. “It’s an endless treasure chest we can keep opening for new discoveries. We continue on in the hopes of mitigating disease or developing a new field application.”

Rush advises young scientists to persevere in their research. “Don’t let anyone tell you that you can’t do it, or you don’t have the right cut. Ignore them, and never give up. You’ve got to have tough skin and just keep going. There will be positive people who support you.”

After years of travel for work and other opportunities, Rush said he’s excited to be settled in East Tennessee, where he and his wife just welcomed their first child. “It’s a beautiful area here, with four distinct seasons and the beauty of the Smokies.” He also appreciates the area’s college football culture and is often seen sporting an LSU lanyard.

“It’s a rebuilding season for LSU,” Rush said. “So, I think UT has a good chance in the Tennessee–LSU matchup. But Geaux Tigers! Hopefully, one of us can at least beat ‘Bama.” —Stephanie Seay

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