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Published on: August 12, 2019
Multiple Origins of the Pathogenic Yeast Candida orthopsilosis by Separate Hybridizations between Two Parental
Markus S Schröder1, Kontxi Martinez de San Vicente1, Tâmara H R Prandini2
1School of Biomedical and Biomolecular Science and UCD Conway Institute of Biomolecular and Biomedical Research, Conway Institute, University College Dublin, Belfield, Dublin, Ireland.
Abstract:
Mating between different species produces hybrids that are usually asexual and stuck as diploids, but can also lead to the formation of new species. Here, we report the genome sequences of 27 isolates of the pathogenic yeast Candida orthopsilosis. We find that most isolates are diploid hybrids, products of mating between two unknown parental species (A and B) that are 5% divergent in sequence. Isolates vary greatly in the extent of homogenization between A and B, making their genomes a mosaic of highly heterozygous regions interspersed with homozygous regions. Separate phylogenetic analyses of SNPs in the A- and B-derived portions of the genome produces almost identical trees of the isolates with four major clades. However, the presence of two mutually exclusive genotype combinations at the mating type locus, and recombinant mitochondrial genomes diagnostic of inter-clade mating, shows that the species C. orthopsilosis does not have a single evolutionary origin but was created at least four times by separate interspecies hybridizations between parents A and B. Older hybrids have lost more heterozygosity. We also identify two isolates with homozygous genomes derived exclusively from parent A, which are pure non-hybrid strains. The parallel emergence of the same hybrid species from multiple independent hybridization events is common in plant evolution, but is much less documented in pathogenic fungi.
Insights
Pathogenic yeast Candida orthopsilosis genomes reveal most isolates are diploid hybrids formed by interspecies mating. This species arose independently at least four times, a rare event in pathogenic fungi.
Area of Science:
- Mycology
- Evolutionary Biology
- Genomics
Background:
- Hybridization between species can lead to new species formation.
- Pathogenic fungi present unique evolutionary dynamics.
- Candida orthopsilosis is a significant human pathogen.
Purpose of the Study:
- To investigate the genomic basis of Candida orthopsilosis evolution.
- To understand the origins and diversification of this pathogenic yeast.
- To identify hybridization events as a mechanism for species formation.
Main Methods:
- Whole-genome sequencing of 27 Candida orthopsilosis isolates.
- Phylogenetic analysis of single nucleotide polymorphisms (SNPs).
- Analysis of mating type and mitochondrial genomes.
Main Results:
- Most Candida orthopsilosis isolates are diploid hybrids from two divergent parental species (A and B).
- Genomes exhibit mosaicism with varying heterozygosity.
- Phylogenetic analyses indicate at least four independent hybridization events created the species.
- Two non-hybrid, homozygous isolates exclusively from parent A were identified.
Conclusions:
- Candida orthopsilosis is a hybrid species with multiple independent origins.
- Hybridization is a significant driver of pathogenic fungal evolution.
- Older hybrids show reduced heterozygosity, reflecting evolutionary time.
