Sexual attraction: On the role of fungal pheromone/receptor systems (A review)

Pheromones have been detected in all fungal phylogenetic lineages. This came as a surprise, as the general role of pheromones in mate attraction was not envisioned for some fungi. Pheromones and pheromone receptor genes have been identified, however, in members of all true fungal lineages, and even for mycelia forming organisms of plant and amoeba lineages, like oomycetes and myxomycetes. The mating systems and genes governing the mating type are different in fungi, ranging from bipolar with two opposite mating types to tetrapolar mating systems (with four possible mating outcomes, only one of which leads to fertile sexual development) in homobasidioymcetes with more than 23,000 mating types occurring in nature. Pheromones and receptors specifically recognizing these pheromones have evolved with slightly different functions in these different systems. This review is dedicated to follow the evolution of pheromone/receptor systems from simple, biallelic bipolar systems to multiallelic, tetrapolar versions and to explain the slightly different functions the pheromone recognition and subsequent signal transduction cascades within the fungal kingdom. The biotechnological implications of a detailed understanding of mating systems for biological control and plant protection, in medicine, and in mushroom breeding are discussed.