title: Expansion of the pseudo-autosomal region and ongoing recombination suppression in the Silene latifolia sex chromosomes.
abstract: There are two very interesting aspects to the evolution of sex chromosomes: what happens after recombination between these chromosome pairs stops and why suppressed recombination evolves. The former question has been intensively studied in a diversity of organisms, but the latter has been studied largely theoretically. To obtain empirical data, we used codominant genic markers in genetic mapping of the dioecious plant Silene latifolia, together with comparative mapping of S. latifolia sex-linked genes in S. vulgaris (a related hermaphrodite species without sex chromosomes). We mapped 29 S. latifolia fully sex-linked genes (including 21 newly discovered from transcriptome sequencing), plus 6 genes in a recombining pseudo-autosomal region (PAR) whose genetic map length is ∼25 cM in both male and female meiosis, suggesting that the PAR may contain many genes. Our comparative mapping shows that most fully sex-linked genes in S. latifolia are located on a single S. vulgaris linkage group and were probably inherited from a single autosome of an ancestor. However, unexpectedly, our maps suggest that the S. latifolia PAR region expanded through translocation events. Some genes in these regions still recombine in S. latifolia, but some genes from both addition events are now fully sex-linked. Recombination suppression is therefore still ongoing in S. latifolia, and multiple recombination suppression events have occurred in a timescale of few million years, much shorter than the timescale of formation of the most recent evolutionary strata of mammal and bird sex chromosomes.
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Lab, Edinburgh EH9 3JT, United Kingdom.
authors.forename: Roberta
authors.initials: R
authors.lastname: Bergero
authors.forename: Suo
authors.initials: S
authors.lastname: Qiu
authors.forename: Alan
authors.initials: A
authors.lastname: Forrest
authors.forename: Helen
authors.initials: H
authors.lastname: Borthwick
authors.forename: Deborah
authors.initials: D
authors.lastname: Charlesworth
mesh_terms: D005075:Biological Evolution; D002874:Chromosome Mapping; D032461:Chromosomes, Plant / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D008040:Genetic Linkage; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D012730:Sex Chromosomes / Q000235:genetics*; D019849:Sex Determination Processes; D029751:Silene / Q000235:genetics / Q000502:physiology*
keywords: Silene latifolia; genetic map; pseudo-autosomal region; recombination suppression; sex chromosomes