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Linkage to the mating-type locus across the genus Microbotryum: Insights into non-recombining chromosomes

Department of Biology, Amherst College, Amherst, Massachusetts 01002 Ecologie, Systématique et Evolution, Université Paris-Sud, F-91405 Orsay, France Comparative Genomics Group CRG-Centre for Genomic Regulation, Doctor Aiguader, 88, 08003 Barcelona, Spain Centro de Recursos Microbiológicos, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal INRA, Unité de Recherche Génomique-Info, 78000 Versailles, France Genoscope, Centre National de Séquençage, UMR CNRS 8030, 2 rue Gaston Crémieux, CP 5706, 91507 Evry, France Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142 Department of Biology, Program on Disease Evolution, University of Louisville, Louisville, Kentucky 40292 E-mail: .
Evolution (Impact Factor: 4.66). 06/2012; DOI: 10.1111/j.1558-5646.2012.01703.x

ABSTRACT Parallels have been drawn between the evolution of nonrecombining regions in fungal mating-type chromosomes and animal and plant sex chromosomes, particularly regarding the stages of recombination cessation forming evolutionary strata of allelic divergence. Currently, evidence and explanations for recombination cessation in fungi are sparse, and the presence of evolutionary strata has been examined in a minimal number of fungal taxa. Here, the basidiomycete genus Microbotryum was used to determine the history of recombination cessation for loci on the mating-type chromosomes. Ancestry of linkage with mating type for 13 loci was assessed across 20 species by a phylogenetic method. No locus was found to exhibit trans-specific polymorphism for alternate alleles as old as the mating pheromone receptor, indicating that ages of linkage to mating type varied among the loci. The ordering of loci in the ancestry of linkage to mating type does not agree with their previously proposed assignments to evolutionary strata. This study suggests that processes capable of influencing divergence between alternate alleles may act at loci in the nonrecombining regions (e.g., gene conversion) and encourages further work to dissect the evolutionary processes acting upon genomic regions that determine mating compatibility

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