Saprotrophy-to-symbiosis continuum in fungi

Fungi are one of the most diverse and ecologically important groups of organisms on Earth. They exhibit remarkable diversity in their ecological roles, ranging from decomposers to mutualistic symbionts to parasites. They have a wide array of lifestyles, which reflect their diverse ecological roles and evolutionary adaptations to marine, aquatic, and terrestrial ecosystems. Fungi are osmotrophs that grow as filaments of cells (hyphae) into their food, secrete digestive enzymes across their cells' chitinous walls, and absorb dissolved nutrients. The classification of fungal lifestyles is primarily based on how they obtain nutrients, with the major modes of nutrition being saprotrophy, parasitism, mutualism and commensalism. Here, we briefly explore these various lifestyles, illustrating their significance in ecosystems and their relationships with other organisms, and then discuss how comparative genomics provides novel insights into their evolutionary trajectories.