Navigating the labyrinth – searching for mechanistic clues to explain the evolution of sequestrate Agaricales with labyrinthine internal chambers

Fungi exhibit a wide range of sporophore morphologies. Amongst the Agaricomycetes, sporophores include mushroom, coralloid, bracket and sequestrate forms. A striking observation is the repeated independent evolution of sequestrate forms, which have arisen more than 100 times from lineages where exposed spore-bearing tissues are the ancestral condition. Here we review the evolution of a particular sequestrate morphology in Agaricales, the labyrinthine sequestrate syndrome. We draw on knowledge of genetic mechanisms involved in sporophore development of agarics (mushrooms) and suggest potential genetic changes in relation to the alterations to pileus, lamellae and stipe during development. We discuss mechanisms that could give rise to the sequestrate syndrome.