Sequence and analysis of the genome of the pathogenic yeast Candida orthopsilosis

Candida orthopsilosis is closely related to the fungal pathogen Candida parapsilosis. However, whereas C. parapsilosis is a major cause of disease in immunosuppressed individuals and in premature neonates, C. orthopsilosis is more rarely associated with infection. We sequenced the C. orthopsilosis genome to facilitate the identification of genes associated with virulence. Here, we report the de novo assembly and annotation of the genome of a Type 2 isolate of C. orthopsilosis. The sequence was obtained by combining data from next generation sequencing (454 Life Sciences and Illumina) with paired-end Sanger reads from a fosmid library. The final assembly contains 12.6 Mb on 8 chromosomes. The genome was annotated using an automated pipeline based on comparative analysis of genomes of Candida species, together with manual identification of introns. We identified 5700 protein-coding genes in C. orthopsilosis, of which 5570 have an ortholog in C. parapsilosis. The time of divergence between C. orthopsilosis and C. parapsilosis is estimated to be twice as great as that between Candida albicans and Candida dubliniensis. There has been an expansion of the Hyr/Iff family of cell wall genes and the JEN family of monocarboxylic transporters in C. parapsilosis relative to C. orthopsilosis. We identified one gene from a Maltose/Galactoside O-acetyltransferase family that originated by horizontal gene transfer from a bacterium to the common ancestor of C. orthopsilosis and C. parapsilosis. We report that TFB3, a component of the general transcription factor TFIIH, undergoes alternative splicing by intron retention in multiple Candida species. We also show that an intein in the vacuolar ATPase gene VMA1 is present in C. orthopsilosis but not C. parapsilosis, and has a patchy distribution in Candida species. Our results suggest that the difference in virulence between C. parapsilosis and C. orthopsilosis may be associated with expansion of gene families

The genomic architecture of the passerine MHC region : High repeat content and contrasting evolutionary histories of single copy and tandemly duplicated MHC genes

The major histocompatibility complex (MHC) is of central importance to the immune system, and an optimal MHC diversity is believed to maximize pathogen elimination. Birds show substantial variation in MHC diversity, ranging from few genes in most bird orders to very many genes in passerines. Our understanding of the evolutionary trajectories of the MHC in passerines is hampered by lack of data on genomic organization. Therefore, we assembled and annotated the MHC genomic region of the great reed warbler (Acrocephalus arundinaceus), using long-read sequencing and optical mapping. The MHC region is large (>5.5 Mb), characterized by structural changes compared to hitherto investigated bird orders and shows higher repeat content than the genome average. These features were supported by analyses in three additional passerines. MHC genes in passerines are found in two different chromosomal arrangements, either as single copy MHC genes located among non-MHC genes, or as tandemly duplicated tightly linked MHC genes. Some single copy MHC genes are old and putative orthologues among species. In contrast tandemly duplicated MHC genes are monophyletic within species and have evolved by simultaneous gene duplication of several MHC genes. Structural differences in the MHC genomic region among bird orders seem substantial compared to mammals and have possibly been fuelled by clade-specific immune system adaptations. Our study provides methodological guidance in characterizing complex genomic regions, constitutes a resource for MHC research in birds, and calls for a revision of the general belief that avian MHC has a conserved gene order and small size compared to mammals

Contrasting evolutionary genome dynamics between domesticated and wild yeasts

International audienceStructural rearrangements have long been recognized as an important source of genetic variation, with implications in phenotypic diversity and disease, yet their detailed evolutionary dynamics remain elusive. Here we use long-read sequencing to generate end-to-end genome assemblies for 12 strains representing major subpopulations of the partially domesticated yeast Saccharomyces cerevisiae and its wild relative Saccharomyces paradoxus. These population-level high-quality genomes with comprehensive annotation enable precise definition of chromosomal boundaries between cores and subtelomeres and a high-resolution view of evolutionary genome dynamics. In chromosomal cores, S. paradoxus shows faster accumulation of balanced rearrangements (inversions, reciprocal translocations and transpositions), whereas S. cerevisiae accumulates unbalanced rearrangements (novel insertions, deletions and duplications) more rapidly. In subtelomeres, both species show extensive interchromosomal reshuffling, with a higher tempo in S. cerevisiae. Such striking contrasts between wild and domesticated yeasts are likely to reflect the influence of human activities on structural genome evolution