Lessons from the Nakaseomyces: mating-type switching, DSB repair and evolution of Ho

This short paper aims to review what our recent studies in the Nakaseomyces yeasts, principally Candida glabrata, reveal about the evolution of the mating-type switching system and its components, as well as about the repair of chromosomal double-strand breaks in this clade. In the model yeast Saccharomyces cerevisiae, the study of mating-type switching has, over the years, led to major discoveries in how cells process chromosomal breaks. Indeed, in this species, switching, which allows every haploid cell to produce cells of opposite mating types that can mate together, is initiated by the Ho endonuclease, linking sexual reproduction to a programmed chromosomal cut. More recently, the availability of other yeasts' genomes from type strains and from populations, and the ability to manipulate and edit the genomes of most yeasts in the laboratory, has enabled scientists to explore mating-type switching in new species, thus enriching our evolutionary perspective on this phenomenon. In this review, we will show how the study of mating-type switching in C. glabrata and Nakaseomyces delphensis has allowed us to reveal possible additional roles for Ho, and also to discover major differences in DSB repair at central and subtelomeric sexual loci. In addition, we report how the study of repair of chromosomal breaks induced by CRISPR-Cas9 reveals that efficient and faithful NHEJ is a major repair pathway in C. glabrata.