A tale of sex and sex-change in yeasts
SémIDEEV à GQE-Le Moulon
En visioconférence en se connectant à : https://eu.bbcollab.com/guest/1514f353e3bf49cbb0b8f193662046b0
Vendredi 5 juin 2020 à 14h00
Cécile FAIRHEAD
Professeure à l’Université Paris-Saclay, responsable de l’équipe SECF, GQE-Le Moulon
invitée par la Direction de GQE-Le Moulon
A tale of sex and sex-change in yeasts
Abstract
Mating-type switching, ie the capacity of haploid cells to convert from one mating-type to the other, is quite frequently observed in yeasts, the most studied example being that of the model yeast, Saccharomyces cerevisiae. These yeasts are “homothallic”, since a single spore germinating after meiosis can give rise to diploid cells, through mating-type switching of haploids, and subsequent mating of haploid cells of opposite mating types. The mechanism for mating-type switching involves a gene conversion event that physically replaces the MAT locus with the DNA sequence from the opposite mating-type, present ectopically in the genome. Thus, three mating-type-like (MTL) loci are present, dubbed “cassettes”. The switch is initiated by Ho, a protein encoded by a gene related to the family of Inteins and Homing-Endonuclease Genes (HEGs). These are “selfish” genes that propagate as self-splicing introns in genes and bring no apparent phenotype to cells, apart from the fact that they carry this invasive selfish gene. Many species phylogenetically close to S. cerevisiae switch, using the same, homologous mechanism, relying on cassettes and Ho. We are studying the evolution of sexual reproduction and switching in the clade of Nakaseomyces yeasts, which includes environmental and pathogenic species. Pathogenic species are described as asexual, as is usual for fungal pathogens of humans, although they have kept the cassettes and the HO gene. We are also interested in population structure of infectious species, its relation to sexual reproduction, and the evolutionary history of these “emerging” opportunistic pathogens of humans. I will report on our recent experimental results and also on the structure of the population of Candida glabrata, the most common pathogen from the Nakaseomyces clade of yeasts.