Hybrids unleashed: exploring the emergence and genomic insights of pathogenic yeast hybrids

Abstract

Hybridisation is the crossing of two divergent lineages that give rise to offspring carrying an admixture of both parental genomes. Genome sequencing has revealed that this process is common in the Saccharomycotina, where a growing number of hybrid strains or species, including many pathogenic ones, have been recently described. Hybrids can display unique traits that may drive adaptation to new niches, and some pathogenic hybrids have been shown to have higher prevalence over their parents in human and environmental niches, suggesting a higher fitness and potential to colonise humans. Here, we discuss how hybridisation and its genomic and phenotypic outcomes can shape the evolution of fungal species and may play a role in the emergence of new pathogens.

Figure 1

Genomic signature features of hybrid yeasts. (a) Schematic representation of a hybridisation event between two diploid homozygous parental lineages A and B. The genome of the resulting diploid hybrid harbours regions that have undergone LOH favouring parental A (blue) or parental B (red). The LOH blocks are surrounded by heterozygous regions where one allele has been inherited from parent A and the other one from parent B. (b) Plots showing the frequency of k-mers in short-read sequencing data of two non-hybrid strains (left and middle panel) and a hybrid (right panel). The first peak in the hybrid corresponds to heterozygous regions, whereas the second, with twice as much coverage, represents genomic regions that have undergone LOH.

Figure 2

Hybridisations are common in the C. parapsilosis species complex. Cladogram depicting the phylogenetic relationships between species in the C. parapsilosis species complex. Hybrids are highlighted in purple. Parental lineages, only known for C. orthopsilosis, are shown in blue and red. Unknown parental lineages are indicated with a question mark. Origins of isolation are depicted with a schematic silhouette of a human (for clinical origin), a wave (for marine origin) or a beverage.