Genetic insights unlock world of mushrooms
Mushrooms are the fruiting bodies of mushroom-forming fungi. The majority of a mushroom-forming fungus consists of mycelium, which is a large network of threads that colonises dead trees or soil. “At some point, this mycelium decides to form a mushroom in order to spread its spores,” explains Mushroomics project coordinator Robin Ohm from Utrecht University in the Netherlands. “So, when you see a mushroom in the forest, what you are seeing really is only the tip of the iceberg. The vast majority of the organism actually lives underground.” Very little is known about how mushroom-forming fungi grow these beautiful mushrooms. How do they decide where this takes place? And which genes are involved in developing these complicated structures?
New fungal research techniques developed
Addressing these questions was a central goal of the Mushroomics project, funded by the European Research Council. “We were especially interested in a class of genes called transcription factors,” notes Ohm. “These genes can act as genetic switches, and as such they can regulate important developmental processes.” Several of these transcription factors were known at the beginning of the project, but nothing was known about how they actually influence development. One reason for this is that it has historically been very difficult to genetically study mushroom-forming fungi. The project team therefore began by developing new genetic techniques for mushrooms. These included a CRISPR/Cas9 protocol, which allows for genes to be deleted from the mushroom genome. The team also sequenced the genomes of several strains of the mushroom Schizophyllum commune, and developed techniques to determine how transcription factors activate other genes.
Key factors in mushroom development identified
Having developed these techniques, Ohm and his colleagues proceeded to study various aspects of mushroom development. “We studied dozens of transcription factors, many of which turned out to play a role in mushroom development,” he says. “For example, if we deleted certain transcription factors from the genome, then no mushroom was formed, or development was stuck at an early stage.” Critically the project discovered a transcription factor that plays an important role in regulating wood degradation. When this was deleted from the genome, the fungus no longer degraded or ate cellulose (a major component of wood). “It turns out that this transcription factor activates numerous genes during growth on wood,” explains Ohm. “Several of those are known cellulose-degrading enzymes, but also numerous unknown genes are activated that we are now studying further.”
More efficient and sustainable cultivation
One reason why this is such an important discovery is that degrading dead wood enables nutrients to be recycled. Another reason is that many species of mushroom are grown commercially for consumption. By feeding on low-quality agricultural waste streams such as wood, straw and manure, they are able to turn biomass into high-quality food. “Despite the importance of mushrooms, we have known very little about how they actually grow,” adds Ohm. “Our results have been able to provide some fundamental insights here.” Using the techniques developed in the course of this project, Ohm and his team are continuing to study the regulatory network of additional transcription factors. “One hope is that new insights into mushroom development will eventually lead to more efficient cultivation,” he says. “This could allow us to reduce society’s meat consumption, and replace it with a more sustainable alternative: mushrooms.”
Keywords
Mushroomics, genetic, fungi, mycelium, spores, CRISPR, genome
