Comparative genomics of the Nakaseomyces clade: Candida glabrata and enew merging pathogens

All authors wish to acknowledge the work of colleagues and collaborators who are authors of the final paper in preparation; International audience; C. glabrata has become the second fungal pathogenic agent of human illness after C. albicans, and two new species, C. nivariensis and C. bracarensis, have been described as emerging pathogens from the clade of the Nakaseomyces. We have sequenced these genomes and that of the other three environmental yeasts from the clade. These species share with Saccharomyces the common ancestor which underwent a whole genome duplication. Nonetheless, chromosome number is highly variable in the clade with some low chromosome numbers. Centromeres show less conservation than expected, as do telomeric repeats. All species share genomic and physiological features that define their monophylogeny. These include genome size and gene number, the presence of insertions in non coding RNA genes, loss of genes from metabolic pathways such as GAL and BNA, and absence of active transposable elements. All contain homologs of genes involved in mating, although most species are described as asexual, and all contain a putative HO gene, enabling mating-type switching in Saccharomyces. Indeed, sexual species in the clade are homothallic and may share with S. cerevisiae the HO gene and three duplicated cassettes. Nonetheless, variations are observed in the chromosomal structure of the cassettes. Other features are common only to C. glabrata and closest species. These include duplicated genes encoding ribosomal proteins, for example. We will report on gene family expansions and contractions in species, on specific features of pathogens, and on specificities of C. glabrata, such as tandem amplification of genes involved in virulence.