Evolutionary Genomics of Sex

Invited talk at PAG XXVIII conference in San Diego, CA, USA

I was delighted to give a talk in a fantastic section “#SexChromosomes and #SexDetermination” at the Plant and Animal Genome Conference XXVIII, #PAGXXVIII, organised by Prof. Ray Ming from University of Illinois at Urbana-Champaign. Many thanks for the invitation! Happy to talk about fungal sex chromosome evolution and #DifferentialExpression


Degenerative mutations in non-recombining regions, such as on sex chromosomes, may lead to differential expression between alleles if mutations occur stochastically in one or the other allele. Reduced allelic expression due to degeneration has indeed been suggested to occur in various sex-chromosome systems. However, whether an association occurs between specific signatures of degeneration and differential expression between alleles has not been extensively tested, and sexual antagonism can also cause differential expression on sex chromosomes. The anther-smut fungus Microbotryum lychnidis-dioicae is ideal for testing associations between specific degenerative signatures and differential expression because: 1) there are multiple evolutionary strata on the mating-type chromosomes, reflecting successive recombination suppression linked to mating-type loci, 2) separate haploid cultures of opposite mating types help identify differential expression between alleles, and 3) there is no sexual antagonism as a confounding factor accounting for differential expression. We found that differentially-expressed genes were enriched in the four oldest evolutionary strata compared to other genomic compartments, and that, within compartments, several signatures of sequence degeneration were greater for differentially-expressed than non-differentially expressed genes. Two particular degenerative signatures were significantly associated with lower expression levels within differentially-expressed allele pairs: upstream insertion of transposable elements and mutations truncating the protein length. Other degenerative mutations associated with differential expression included non-synonymous substitutions and altered intron or GC content. The association between differential expression and allele degeneration is relevant for a broad range of taxa where mating compatibility or sex is determined by genes located in large regions where recombination is suppressed.