Sex-Induced Silencing Operates During Opposite-Sex and Unisexual Reproduction in Cryptococcus neoformans

Abstract

Cryptococcus neoformans is a human fungal pathogen that undergoes a dimorphic transition from yeast to hyphae during a-α opposite-sex mating and α-α unisexual reproduction (same-sex mating). Infectious spores are generated during both processes. We previously identified a sex-induced silencing (SIS) pathway in the C. neoformans serotype A var. grubii lineage, in which tandem transgene arrays trigger RNAi-dependent gene silencing at a high frequency during a-α opposite-sex mating, but at an ∼250-fold lower frequency during asexual mitotic vegetative growth. Here we report that SIS also operates during α-α unisexual reproduction. A self-fertile strain containing either SXI2a-URA5 or NEO-URA5 transgene arrays exhibited an elevated silencing frequency during solo and unisexual mating compared with mitotic vegetative growth. We also found that SIS operates at a similar efficiency on transgene arrays of the same copy number during either α-α unisexual reproduction or a-α opposite-sex mating. URA5-derived small RNAs were detected in the silenced progeny of α-α unisexual reproduction and RNAi core components were required, providing evidence that SIS induced by same-sex mating is also mediated by RNAi via sequence-specific small RNAs. In addition, our data show that the SIS RNAi pathway also operates to defend the genome via squelching transposon activity during same-sex mating as it does during opposite-sex mating. Taken together, our results confirm that SIS is conserved between the divergent C. neoformans serotype A and serotype D cryptic sibling species.