Friend or enemy? Researchers explore ancient partnership between moss and fungi

The next time you’re walking through the woods in the dead of winter, take a moment to see if you can spot one of nature’s most persistent and heartfelt survivors.

No, not the patch of brown grass peeking through a snowbank, nor the acres of trees with bare branches waiting for spring.

Look down and you’ll find that the only green to see is right under your boot: a lush carpet of moss.

For Björn Hamberger, James K. Billman Jr., MD, endowed professor in the Department of Biochemistry and Molecular Biology at the Michigan State University College of Natural Science, this year-round endurance is in itself a cause for admiration.

“That gives you an idea of ​​how resilient these organisms are, and that’s probably one of the reasons why mosses stuck around and weren’t lost through evolution,” Hamberger said.

But it is also a starting point for research spanning centuries, from ancient Earth to humanity’s future in space. Appearing in The Plant Journal, The latest paper from the Hamberger lab seeks to better understand how mosses and other plants conquered our planet and how, to do so, they were able to get much-needed help from their long-time collaborators, fungi.

From early Earth to future Mars

Mosses made their transition to dry land 450 million years ago, during the Ordovician period, a process that Hamberger says could not have succeeded without teamwork.

When the mosses made landfall, they had to account for a host of new and complex variables, including water regulation, gravity, fluctuating temperatures and exposure to UV light.

Fortunately, the mosses encountered a landscape already colonized by early fungi whose root networks, or mycelium, could absorb essential nutrients from the Earth. In exchange for these nutrients, early land plants provided fungi with a source of carbon, initiating a new relationship that continues to this day.

“At least 80 percent of modern plants still collaborate in some way with fungi, getting help to become stronger and more resilient,” Hamberger explained. “As we envision a future in which plants need to support a growing population, this will be a critical factor.”

Working with mosses for more than a decade, Hamberger and his research group participated in a special exhibit at the Detroit Science Gallery called “Fog of Dawn” in 2019, which featured mosses growing in terrariums aimed at mimicking the ambience of the primordial Earth and the subsequent takeover. plants and mushrooms.

The group also engineered moss to express foreign, modern biochemical pathways between land plants and produce products such as patchouli oil.

Hamberger sees exciting potential here in the field of space exploration. Mosses and other plants could act as natural manufacturers of building materials or medicines while converting carbon dioxide into oxygen during spaceflight.

“If you can take plants with you on such a journey and give them the blueprints for creating useful products, it will reduce the immense weight of raw materials in orbit,” Hamberger said. “Plus, when it comes to terraforming a place like Mars, why not start with moss, a plant that has already successfully altered our own planet?”

With their latest research in The plant journalThe Hamberger lab hopes to shed more light on plant-microbe interactions and uncover the ways moss and fungi communicate at the microscopic level.

Friend or enemy?

To achieve these goals, Hamberger and Davis Mathieu, a doctoral student and first author of the paper, designed an experiment that would provide a front-row seat to real-time moss-fungus interactions.

For three months, the laboratory observed the moss, Physcomitrium patens, colonizing different terrariums. Some habitats were entirely devoid of fungi, while others were co-cultivated with two species of the terrestrial fungal lineage, Mortirellaceae, which likely existed at the same time as plants began to take over the land.

The mushrooms were provided by fungi and genetics expert Greg Bonito, an associate professor in MSU’s Department of Plant, Soil and Microbial Sciences and a longtime collaborator of Hamberger.

Using microscopy, genetic analysis and Raspberry Pi microcomputers, the researchers tracked the subtle but distinct ways in which the moss interacted with its fungal neighbors. The team discovered that these interactions depended on a unique addition to the distribution: endobacteria within the fungi.

These endobacteria posed a difficult question themselves. Endobacteria are entirely dependent on their fungal host for survival, but it was unclear whether they provided any value to this relationship.

“In general, endobacteria are not considered beneficial to fungi, with cells undergoing significant compromises to accommodate them,” Mathieu said. “This of course begs the question: why are they still here?”

Mathieu and others have found that when endobacteria are present, fungi can more easily interact with their mossy neighbors. As they experimented with fungi stripped of endobacteria, a complex web of relationships began to emerge.

For example, one species of fungus appeared to “eat” moss from the inside when its endobacteria were present. But in the samples where endobacteria were absent?

“He lives side by side with the moss, totally indifferent,” explains Mathieu.

Meanwhile, another species of fungus that provided moss benefits changed its behavior when its endobacteria were removed. The fungi began producing spore-like structures, indicative of stress, and no longer colonized the moss as they once did.

The Hamberger lab is eager to better understand these friend-foe relationships between moss, fungi, and endobacteria, and what these findings mean for understanding life on Earth.

“We thought we would start with something simple and straightforward: the beginning of land plant life,” Hamberger quipped. “But it turns out that there is a very exciting and very complex story that can tell us something about what happened in the evolution of land plants, what brought us to this planet and what which could take us to another planet.”

He also hopes that this research could spark interest in the crucial life forms that we encounter every day, often without realizing it.

“Maybe it could inspire a little appreciation for these cool organisms that can live in harsh conditions and are the first in the spring to say, ‘Yeah, let’s go,’ when the snow melts and the light the sun is coming back.”