Sexual reproduction between partners of the same mating type in Cryptococcus neoformans.

Cryptococcus neoformans is a globally distributed human fungal pathogen that causes life-threatening meningoencephalitis in immunocompromised patients. It has a defined sexual cycle involving haploid cells of alpha and a mating types, yet the vast majority of environmental and clinical isolates are alpha (ref. 3). Sexual recombination is normally expected to occur between isolates of opposite mating type in organisms with two mating types (or sexes). How sexual reproductive potential can be maintained in an organism with a largely unisexual, nearly clonal population genetic structure is unknown. One clue, however, is that alpha strains undergo fruiting, a process that resembles sexual mating but is thought to be strictly mitotic and asexual. We report here that hallmarks of mating occur during fruiting, including diploidization and meiosis. Pheromone response pathway elements and the key meiotic regulator Dmc1 are required for efficient fruiting. Furthermore, fusion and meiosis can occur between non-isogenic alpha strains, enabling genetic exchange. These studies reveal how sexual reproduction can occur between partners of the same mating type. These findings have implications for the evolution of microbial pathogens, as well as for parthenogenesis, cell fusion events and transitions between self-fertilizing and outcrossing modes of reproduction observed in both fungi and other kingdoms.