A coupled process of same- and opposite-sex mating generates polyploidy and genetic diversity in Candida tropicalis

Abstract

Sexual reproduction is a universal mechanism for generating genetic diversity in eukaryotes. Fungi exhibit diverse strategies for sexual reproduction both in nature and in the laboratory. In this study, we report the discovery of same-sex (homothallic) mating in the human fungal pathogen Candida tropicalis. We show that same-sex mating occurs between two cells carrying the same mating type (MTLa/a or α/α) and requires the presence of pheromone from the opposite mating type as well as the receptor for this pheromone. In ménage à trois mating mixes (i.e., “a x a + α helper” or “α x α + a helper” mixes), pheromone secreted by helper strains promotes diploid C. tropicalis cells to undergo same-sex mating and form tetraploid products. Surprisingly, however, the tetraploid mating products can then efficiently mate with cells of the opposite mating type to generate hexaploid products. The unstable hexaploid progeny generated from this coupled process of same- and opposite-sex mating undergo rapid chromosome loss and generate extensive genetic variation. Phenotypic analysis demonstrated that the mating progeny-derived strains exhibit diverse morphologies and phenotypes, including differences in secreted aspartic proteinase (Sap) activity and susceptibility to the antifungal drugs. Thus, the coupling of same- and opposite-sex mating represents a novel mode to generate polyploidy and genetic diversity, which may facilitate the evolution of new traits in C. tropicalis and adaptation to changing environments.

Advances in understanding the evolution of fungal genome architecture

“…Another study found that the genome reduction in this parasexual cycle involves recombination, similar to meiosis observed in other organisms, and thus has been termed para-meiosis 126 . A closely related species, Candida tropicalis, was found to exhibit a combination of same- and opposite-sex mating to generate polyploidy, which in turn increases genetic diversity 127 .…”

Is Candida auris sexual?

“…It is speculated that unisexual reproduction in Cryptococcus neoformans benefits the species as it prevents deleterious mutations from accumulating and can also yield progeny with enhanced fitness [8,23]. Unisexual mating can also occur in C. albicans and Candida tropicalis, but only in the presence of the opposite mating pheromone [24,25].…”

“…This would render clade I MTLa strains sterile due to an inability to export a-factor. We cannot exclude the possibility that C. auris, similar to C. albicans and C. tropicalis [24,25], could undergo unisexual reproduction with isolates from within the same clade.…”

“…Unisexual mating can also occur in C . albicans and Candida tropicalis , but only in the presence of the opposite mating pheromone [ 24 , 25 ].…”

“…albicans and C . tropicalis [ 24 , 25 ], could undergo unisexual reproduction with isolates from within the same clade.…”