The following clip is a research feature about endophytes, the fungi that live inside plant tissues, that I wrote for the College of Natural Sciences Office of Communications. It can also be found here: http://cns.utexas.edu/news/you-probably-ate-fungus-today
That salad you had for lunch. Yeah, it had fungi in it.
That celery stick you barely nibbled that came with your basket of wings last night. It had fungi in it too.
And it’s not just the plants you eat; the grass you walk on, the trees you walk under, and the flowers you admire all contain fungi. Actually, every plant tissue ever documented has fungi living inside it. They are called endophytes.
“Essentially most of us think of a plant as just a plant, but these plants are crawling with fungus,” said Christine Hawkes, associate professor of integrative biology in the College of Natural Sciences. “Every leaf, every stem, every root is full of fungus.”
Fungi are ubiquitous in plant tissues but every plant doesn’t contain the same species and most plants usually contain more than one species, potentially leading to vast amounts of undiscovered diversity, Hawkes added.
Endophytes are opening up an entire new frontier in the already swiftly evolving field of microbial ecology, the study of the distribution and interactions of microbes.
Scientists want to understand how the fungi hurt or help their host plant. Inside a plant these fungi can do two things: just hang out, a process called commensalism, or give the plant a variety of benefits in exchange for something, called mutualism.
The plants likely provide spare sugar to the fungi, while the documented benefits to the plant include improved tolerance to stressful conditions such as drought, heat, or salinity, as well as production of chemicals that act as protection against being eaten by herbivores, Hawkes said. While scientists understand some of these benefits, the full spectrum has not been realized and they are far from knowing how the fungi actually confer them to the plant. Teasing apart these benefits and mechanisms is the heart of the research taking place in the Hawkes lab.
While the group is interested in all of these interactions, they have been primarily focusing on drought tolerance. Water is a primary controller of plant productivity, and drought strongly limits production in both agricultural and ranching systems. While Texans may be accustomed to droughts, these conditions are expected to worsen in the future, she said. Fungal endophytes could provide a novel strategy for drought management, which is one goal in the Hawkes lab.
To study the endophytes, the researchers took advantage of a local steep rainfall gradient across the Edwards Plateau, where annual rainfall ranges from about 36 inches per year near Austin to roughly 16 inches by Del Rio. The Edwards Plateau is a region in west-central Texas that is essentially outlined by San Angelo, Austin, San Antonio and Del Rio, with the Hill Country making up its eastern portion.
The gradient allows them to compare fungi from plants that have historically received larger amounts of yearly precipitation to fungi from plants that experience more drought conditions year-round. In addition, by sampling the gradient across multiple years, it is possible to compare how these fungi respond to current conditions vs. historical rainfall.
“I grew up on the East Coast and lived in California,” Hawkes said. “When I moved here, I was thrilled to discover that I was living in one of the best precipitation gradients in the country, and that we were able to access research sites across the gradient through the Texas Parks and Wildlife Department and the Texas EcoLab program.”
Hawkes and her team survey 15-20 sites along the Plateau and collect plant and soil samples each year. They then isolate the fungi growing inside those plant samples. Once isolated, they can study the effects of the fungus on plants in the greenhouse.
Graduate students Hannah Giauque and Elise Worche have isolated and identified about 100 fungi from the Edwards Plateau so far. Giauque studies the effects of the endophytic fungi on drought resistance of switchgrass, a grass that is native to the U.S. prairies, and has shown large potential for use as a biofuel.
She got some surprising results, Hawkes said. They found almost an order of magnitude difference among about 30 endophytes in their effects on plant transpiration efficiency, which is how big a plant can get for the amount of water it uses.
“Essentially that variation is so huge that it suggests the fungus inside the plant matters a lot for how that plant can respond to its environment,” she said. “Which is something we don’t usually think about.”
However, they found that where the fungus came from didn’t necessarily reflect its function. While there were different species across the gradient, the location did not always reflect the ability of a fungus to confer drought tolerance, which was puzzling. A fungus from the dry end of the gradient isn’t necessarily a better mutualist for helping the plant resist drought when compared to one from the wetter side, like one would predict, and they are continuing to research why, Hawkes said. Rainfall is not the only important factor for a plant: some fungi may function as mutualists for the plant in ways that are not related to drought.
Another level of experimentation the researchers are working on is taking place at the Lady Bird Johnson Wildflower Center. There they are using a controlled plot to manipulate rainfall conditions. These rainfall conditions range from extreme drought to historical average to extreme wet, allowing the researchers to test how plants and fungi will respond at a single location to a range of climatic conditions.
Fungi can’t get up and walk around, so limitation in their dispersal may prevent rapid responses to a change in climate. In support of this, endophytic fungal communities across the 400-kilometer Plateau gradient have been stable during the three years the Hawkes lab has been sampling, even with annual changes in drought conditions. By planting grasses across a smaller area but still maintaining a precipitation gradient they are trying to tease apart how the different species end up where they do, and specifically predict how long it would take a new community to assemble in the face of climate change.
Worchel said the fungi don’t actually occur in isolation in nature and numerous species can be found inside one plant — even in just one two-inch leaf section — so the earlier experiments with one fungus in one plant aren’t necessarily representative of how they function in the natural environment. She is trying to learn how the fungi interact with each other but also with the plant when more than one fungus is present.
“I’m trying to figure out what the outcome is if you colonize a plant with both a mutualistic fungus and one that doesn’t have a positive effect,” she said. “Do you end up with a positive effect or does the commensal neutralize any positives? It can get complicated really quickly.”
Hawkes said that using the gradient, the field experiment, and greenhouse experiments provides different approaches to testing mechanisms with different levels of control and that together they create a very cohesive whole.
“The work that we’re doing eventually will help us to determine the potential for the endophytes to play a role in management of these grasses, particularly under drought,” she said. “There’s no final answer yet, but these preliminary results and ongoing experiments are very promising.”
Hawkes and her students are really at the forefront of this field.
“We aren’t building off of an extensive body of science for this,” Hawkes said. “It really is a new frontier. I realize that I could work on these few lines of research for the rest of my life and probably not have an answer. I think it’s both the challenge and what makes it exciting.”
Technological advances will only speed the process that could one day lead to plants that can better withstand climate change and other stresses, she added. At the end of the day, though, the entire lab agrees that the fact that these fungi are all around us is simply fascinating.
When giving talks about her research, especially the time she presented it over a dinner, Hawkes likes to remind everyone that, when they eat their leafy greens and other vegetables, they are also getting a healthy dose of fungus.