Ancient sex compatibility genes underlie tissue differentiation in mushrooms
This study reveals that mushroom fruiting bodies possess bona fide tissues regulated by the co-option of ancient mating pheromone and receptor genes, demonstrating how selection can drive the convergent evolution of complex multicellularity across organisms with fundamentally different cellular architectures.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Complex life often relies on a blueprint. In animals and plants, a single fertilized cell divides and organizes itself into a miniature version of the adult, complete with distinct organs like hearts, leaves, or roots. This process, known as embryogenesis, creates specialized tissues that perform specific jobs. Fungi, however, build their complex structures in a completely different way. Instead of dividing cells to form organs, they grow long, thread-like tubes called hyphae that branch out and weave together. For centuries, scientists have debated whether these woven mats of threads, which form mushrooms, possess true tissues with specialized functions, or if they are merely loose aggregates of similar cells. The question has remained difficult to answer because the threads are microscopic and the structures are tiny, making it hard to see how one part of a mushroom might differ genetically from another.
A team of researchers has now mapped the genetic activity of a mushroom at a level of detail never before achieved, revealing that these fungal structures do indeed possess bona fide tissues. By studying the common ink cap mushroom, they discovered that different regions of the fruiting body turn on unique sets of genes, creating distinct functional zones much like the organs in a human body. Most surprisingly, the genetic system that controls how these mushrooms find mates was found to be the same system that directs the growth of their tissues. This suggests that evolution repurposed an ancient mating signal to solve the complex problem of building a multicellular structure from simple threads.
To uncover these hidden patterns, the researchers turned to a model mushroom called Coprinopsis cinerea. They began by growing the fungus in a controlled environment and waiting for it to form its tiny, developing fruiting bodies. Using a technique called laser-capture microdissection, they sliced the mushroom into extremely thin sections and used a laser to isolate specific, microscopic regions of tissue. They collected samples from nine different types of tissue, ranging from the protective outer skin to the inner core where spores are made, and from the earliest stages of growth to the nearly mature mushroom. Because the samples were so small, the team had to develop specialized methods to extract and sequence the RNA, which acts as a record of which genes are active in each specific spot.
The resulting genetic maps showed a clear division of labor. The researchers found that the outer layers of the mushroom, which protect the delicate interior, expressed genes related to defense and water resistance. These regions produced proteins that repel water and fend off insects or other fungi. In contrast, the inner core tissues, which form the cap, stem, and gills, were busy with genes involved in rapid growth, energy production, and cell division. The gills, which produce the spores, showed a unique genetic signature focused on DNA repair and replication. This clear separation of genetic activity confirmed that the different parts of the mushroom are not just physically distinct but are functionally specialized, operating as true tissues with dedicated roles.
The most unexpected discovery emerged when the researchers looked for the master switches that control this differentiation. They found that the genes most active in specific tissues were not the ones typically associated with development in animals or plants. Instead, the key regulators were genes involved in mating. In fungi, mating usually happens before the fruiting body forms, when two compatible threads fuse together. This process relies on chemical signals called pheromones and receptors that allow threads to recognize a partner. The study revealed that these same pheromone and receptor genes, along with enzymes that help process them, are turned on in specific tissues during the mushroom's growth.
To prove that these genes were actually driving the formation of tissues, the researchers created mutant versions of the mushroom where specific mating genes were disabled. When they removed these genes, the mushrooms failed to develop correctly. Some mutants grew caps that were malformed or stuck together, while others failed to form gills entirely. In some cases, the mushrooms stopped growing at a very early stage. These results demonstrated that the mating system was not just a leftover from the past but was actively required to build the mushroom. The researchers concluded that evolution had co-opted this ancient communication system, which originally helped threads find each other, to now help the threads organize themselves into a complex, multicellular structure.
The study also looked at how these genetic patterns have changed over millions of years. By comparing the mushroom's genes to those of other fungi, the team found that the genes responsible for tissue specialization are ancient, dating back hundreds of millions of years. However, the specific way these genes are used to build tissues appears to be a more recent innovation. The researchers observed that as the mushroom develops, the genetic activity becomes more conserved, meaning the later stages rely on older, more stable genetic programs. This pattern is different from what is seen in animals, where the earliest stages are often the most conserved. In mushrooms, the final tissue to emerge, the gills, expresses the oldest set of genes, reflecting their role as the primary site for spore production.
This work provides the first clear genetic explanation for how mushrooms build their complex shapes. It shows that despite growing from simple threads, these fungi achieve a level of organization comparable to animals and plants. The findings suggest that the ability to form complex tissues is not limited to organisms that grow by cell division but can also arise in organisms that grow by extending threads. By repurposing an ancient mating system to control development, mushrooms found a unique solution to the challenge of building a multicellular body. This discovery bridges a gap in our understanding of how complex life evolves, showing that nature can arrive at similar solutions—specialized tissues and organs—through very different genetic pathways.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.