Abstract
In fungi, unisexual reproduction, where sexual development is initiated without the presence of two compatible mating type alleles, has been observed in several species that can also undergo traditional bisexual reproduction, including the important human fungal pathogens Cryptococcus neoformans and Candida albicans. While unisexual reproduction has been well characterized qualitatively, detailed quantifications are still lacking for aspects of this process, such as the frequency of recombination during unisexual reproduction, and how this compares with bisexual reproduction. Here, we analyzed meiotic recombination during α-α unisexual and a-α bisexual reproduction of C. neoformans. We found that meiotic recombination operates in a similar fashion during both modes of sexual reproduction. Specifically, we observed that in α-α unisexual reproduction, the numbers of crossovers along the chromosomes during meiosis, recombination frequencies at specific chromosomal regions, as well as meiotic recombination hot and cold spots, are all similar to those observed during a-α bisexual reproduction. The similarity in meiosis is also reflected by the fact that phenotypic segregation among progeny collected from the two modes of sexual reproduction is also similar, with transgressive segregation being observed in both. Additionally, we found diploid meiotic progeny were also produced at similar frequencies in the two modes of sexual reproduction, and transient chromosomal loss and duplication likely occurs frequently and results in aneuploidy and loss of heterozygosity that can span entire chromosomes. Furthermore, in both α-α unisexual and a-α bisexual reproduction, we observed biased allele inheritance in regions on chromosome 4, suggesting the presence of fragile chromosomal regions that might be vulnerable to mitotic recombination. Interestingly, we also observed a crossover event that occurred within the MAT locus during α-α unisexual reproduction. Our results provide definitive evidence that α-α unisexual reproduction is a meiotic process similar to a-α bisexual reproduction.
Highlights
Cryptococcus neoformans is a globally distributed basidiomycetous human fungal pathogen that causes life threatening meningoencephalitis [1]
One of the main objectives of our study was to investigate the frequency of recombination during a-a unisexual reproduction in C. neoformans, and how this compares to a-a bisexual reproduction
It has been shown that the strain XL280a can undergo selfing and produce spores, albeit at lower frequency compared to typical a-a bisexual reproduction
Summary
Cryptococcus neoformans is a globally distributed basidiomycetous human fungal pathogen that causes life threatening meningoencephalitis [1]. In response to a variety of environmental cues, a and a cells undergo a well characterized bisexual reproduction cycle in which cells of opposite mating type first undergo cell-cell fusion that is evoked by pheromone secretion and sensing. The resulting dikaryon transitions into hyphal growth and eventually the hyphal tips form basidia fruiting bodies in which nuclear fusion and one round of meiosis occur [9]. Multiple rounds of mitosis and budding produce on the surface of each basidium four long chains of infectious spores, which can be readily aerosolized and cause infections in mice and possibly humans [10]
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