Mycena mushrooms are evolving right before our eyes

In a new study from the Okinawa Institute of Science and Technology (OIST), scientists have discovered that Mycena mushrooms have surprisingly large genomes. This revelation contradicts long-held assumptions about the species. 

Mycena mushrooms were previously believed to be sabrobes, which depend solely on the degradation of dead organic material for nutrients. But the recent findings suggest that these mushrooms harbor richer gene varieties, enabling them to adapt to varying lifestyles based on existing circumstances.

Mycena mushrooms in the harsh Arctic 

The specific strains of Mycena mushrooms spotted in the harsh ecosystem of the Arctic possess some of the largest mushroom genomes ever recorded. 

Their DNA shows evidence of rampant growth across their genetic makeup, inclusive not only of invasion and plant interaction genes but also elements with unknown functions and genes acquired from unrelated fungi through horizontal gene transfer.

Delving into the heart of the discovery, the research team collected Mycena samples across Northern Europe, including the Arctic region. 

“Three of these were successfully sequenced, and we found that these Arctic species contained significantly larger genomes compared to ordinary Mycena species,” explained Dr. Shingo Miyauchi, co-lead author of the study.  

Their initial astonishment led them to double-check the genome assembly’s correctness and conclude that these significantly enlarged genomes were exclusive to certain Arctic Mycena mushroom species.

An evolutionary advantage

“Evolution tells us that non-advantageous traits tend to disappear over time, so an obvious implication is that adaptability and generalism in those large genome structures must be an advantage for these fungi,” said study co-author Francis Martin.

“This is despite the costs of having a large genome with lots of possibly unnecessary features that must be replicated in each cell division. This may be particularly true in an extreme environment like the Arctic, as also seen in plants.”  

Significance of Mycena mushrooms 

The research initiative was primarily driven by Mycena’s crucial role as a significant mushroom decomposer of litter and leaves in forest ecosystems. Despite having minuscule bodies, their contributions to the global carbon cycle are substantial. 

The researchers were also intrigued by the species’ bioluminescent features (they glow in the dark). Given these fascinating characteristics, they sought to expand their understanding of the gene structure in these fungi to learn more about their lifestyle habits.

In the course of the study, the team produced new genome sequences for 24 additional Mycena species, including three Arctic species. 

Focus of the research 

The goal of the research was to comprehend how the genomes evolved over time, what triggered their expansion, and how different species might vary in plant cell wall-degrading enzymes based on their lifestyle habits.

Amidst their findings, the researchers discovered that the genome expansion was a common feature across all Mycena species, affecting all gene families regardless of their expected habits. Two Arctic-collected species exhibited the largest genomes, up to eight times bigger than those found in temperate zones.

The researchers came across another surprising discovery: the Arctic species’ genomes expanded far beyond the general Mycena expansion. The research team also found that Mycena fungi had acquired genes from Ascomycetes through horizontal gene transfer.

“The evolutionary transition from decomposer to symbiotic fungi is generally believed to have happened in parallel in several fungal groups throughout the course of evolution millions of years ago,” said Håvard Kauserud of the University of Oslo. “However, with Mycena, we appear to be seeing this gradual process in action happening right in front of our eyes.”

Future implications of the study

The findings suggest that multiple possible lifestyles are reflected in their genome structures, a conclusion that has significant implications for understanding an organism’s habits from their genome sequences alone.

As the research progresses, the team continues to delve deeper into forest fungi’s genomic intricacies. 

“Our goal is genome mining to uncover unusual genes, enzymes, and metabolites,” said Dr. Miyauchi. “Ultimately, we aim to isolate unique genomic materials for biotechnological applications. It’s my hope that funding bodies recognize the huge future potential of petite mushrooms.”

The study is published in the journal Cell Genomics.

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