Mycena Fungi Evolved To Infect Living Hosts, Show Potential As Plant Root Invaders

Bonnet mushrooms, known by their genus Mycena, have long been thought to be saprotrophic organisms. This means they exclusively feed on nonliving organic matter, such as dead trees. However, a recent study has revealed that this fungal species is in the middle of an evolutionary leap.

From Decomposer to Invader

In this research, Christoffer Bugge Harder and other researchers from the University of Copenhagen's Department of Biology investigated the DNA of Mycena fungi. They discovered that this fungal species is consistently present in the roots of living plant hosts. It indicates that Mycena is in the process of evolutionary development, from being decomposers of dead plants to bevaders of living hosts under favorable conditions.

This phenomenon is not alarming for the researchers. This is because bonnet mushrooms show early signs of participation in mutualism, like when they live in symbiosis with trees. It means they try to establish a cooperative relationship as they find their way into healthy young trees and plants.

From a plant's perspective, Mycena is primarily out to do good. The bonnet mushroom appears to exchange nitrogen with carbon from plants. This means their invasion can be interpreted as an evolutionary courtship where the invader lives in harmony with their living hosts.

This beneficial relationship, however, is not always observed between a bonnet mushroom and its hosts. Once it penetrates the living plant, the fungi can perform any of the three possible actions. They can be harmful parasites that suck the life out of the healthy plant; they can lurk like vultures that harmlessly wait for the plant to die, or they can begin working together. Some species of Mycena are slowly developing the ability to collaborate, though it has yet to be finely tuned.

Challenging the Traditional Roles

This study challenges the traditional beliefs about the ecology of fungi as an unusual group of organisms that is not easy to classify. It also presents the need to reassess the conditions of many organisms, although Mycena is among those that seem to benefit the most.

For instance, other fungi, such as the Amanita genus, are known for collaborating with living plants. Their ability to work together with other organisms developed millions of years ago. However, Amanita have long since lost their ability to survive without the presence of their hosts. Because of this, the Fungi Kingdom was traditionally divided into strictly separate ecological groups: saprophytic, parasitic, or mutualistic.

The genus Mycena seems to lie somewhere between the ecological niches. The strict classification has been increasingly called into question, and according to Harder, their research supports the ambiguity of the lines. Some Mycena found their solution spanning several different ecological roles.

To clarify things, his team looked at the carbon isotopes of Mycena. From the result of their analysis, they concluded that these fungi are not only saprotrophic decomposers but also mutualistic. In some cases, they can also fall under the parasitic category.