Project description:Species within the human pathogenic Cryptococcus species complex are major threats to public health, causing about one million infections globally each year. Cryptococcus amylolentus is the most closely known related species of the pathogenic Cryptococcus species complex, and it is non-pathogenic. Additionally, while pathogenic Cryptococcus species have bipolar mating systems with a single large MAT locus that represents a derived state in Basidiomycetes, C. amylolentus has a tetrapolar mating system with two MAT loci (P/R and HD) located on different chromosomes. Thus, studying C. amylolentus will shed light on the origin and evolution of pathogenesis, as well as the transition from tetrapolar to bipolar mating systems in the pathogenic Cryptococcus species. In this study, we sequenced, assembled, and annotated the genomes of two C. amylolentus isolates, CBS6039 and CBS6273, which are sexual and interfertile. Genome comparison between the two C. amylolentus isolates identified the boundaries and the complete gene contents of the P/R and HD MAT loci. Also, bioinformatics and ChIP-seq analyses showed that C. amylolentus has regional centromeres that are enriched with species-specific transposable and repetitive elements, similar to the centromeric structures in the pathogenic Cryptococcus species. Additionally, we found that while neither of the P/R and HD loci in C. amylolentus is physically linked to its centromere, both MAT loci exhibit centromere linkage in meiosis, suggesting the presence of recombinational suppressors and/or epistatic gene interactions in the inter MAT-CEN regions. Furthermore, genomic comparison between C. amylolentus and pathogenic Cryptococcus species provides evidence that chromosomal rearrangements mediated by intercentromeric recombination have occurred after the two lineages split from their common ancestor. We propose a model in which the evolution of the bipolar mating system was initiated by an ectopic recombination event mediated by repetitive elements located within the centromeric regions and shared between chromosomes. This translocation brought the P/R and HD loci onto the same chromosome, and was followed by chromosomal rearrangements that resulted in the two MAT loci becoming physically linked and eventually fused to form the single contiguous MAT locus that is now extant in the pathogenic Cryptococcus species.

Project description:Sexual reproduction in fungi is governed by a specialized genomic region called the mating-type locus (MAT). The human fungal pathogenic and basidiomycetous yeast Cryptococcus neoformans has evolved a bipolar mating system (a, α) in which the MAT locus is unusually large (>100 kb) and encodes >20 genes including homeodomain (HD) and pheromone/receptor (P/R) genes. To understand how this unique bipolar mating system evolved, we investigated MAT in the closely related species Tsuchiyaea wingfieldii and Cryptococcus amylolentus and discovered two physically unlinked loci encoding the HD and P/R genes. Interestingly, the HD (B) locus sex-specific region is restricted (∼2 kb) and encodes two linked and divergently oriented homeodomain genes in contrast to the solo HD genes (SXI1α, SXI2a) of C. neoformans and Cryptococcus gattii. The P/R (A) locus contains the pheromone and pheromone receptor genes but has expanded considerably compared to other outgroup species (Cryptococcus heveanensis) and is linked to many of the genes also found in the MAT locus of the pathogenic Cryptococcus species. Our discovery of a heterothallic sexual cycle for C. amylolentus allowed us to establish the biological roles of the sex-determining regions. Matings between two strains of opposite mating-types (A1B1×A2B2) produced dikaryotic hyphae with fused clamp connections, basidia, and basidiospores. Genotyping progeny using markers linked and unlinked to MAT revealed that meiosis and uniparental mitochondrial inheritance occur during the sexual cycle of C. amylolentus. The sexual cycle is tetrapolar and produces fertile progeny of four mating-types (A1B1, A1B2, A2B1, and A2B2), but a high proportion of progeny are infertile, and fertility is biased towards one parental mating-type (A1B1). Our studies reveal insights into the plasticity and transitions in both mechanisms of sex determination (bipolar versus tetrapolar) and sexual reproduction (outcrossing versus inbreeding) with implications for similar evolutionary transitions and processes in fungi, plants, and animals.

			Action	DRS
	MEKH01.dat.gz	Other
	MEKH01.fasta.gz	Fasta.gz
	MEKH01.master.dat	Other
	SRR1010369_1.fastq.gz	Fastqsanger.gz
	SRR1010369_2.fastq.gz	Fastqsanger.gz

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Cryptococcus amylolentus CBS 6273

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