title: Mobile Introns Shape the Genetic Diversity of Their Host Genes.
abstract: Self-splicing introns populate several highly conserved protein-coding genes in fungal and plant mitochondria. In fungi, many of these introns have retained their ability to spread to intron-free target sites, often assisted by intron-encoded endonucleases that initiate the homing process. Here, leveraging population genomic data fromSaccharomyces cerevisiae,Schizosaccharomyces pombe, andLachancea kluyveri, we expose nonrandom patterns of genetic diversity in exons that border self-splicing introns. In particular, we show that, in all three species, the density of single nucleotide polymorphisms increases as one approaches a mobile intron. Through multiple lines of evidence, we rule out relaxed purifying selection as the cause of uneven nucleotide diversity. Instead, our findings implicate intron mobility as a direct driver of host gene diversity. We discuss two mechanistic scenarios that are consistent with the data: either endonuclease activity and subsequent error-prone repair have left a mutational footprint on the insertion environment of mobile introns or nonrandom patterns of genetic diversity are caused by exonic coconversion, which occurs when introns spread to empty target sites via homologous recombination. Importantly, however, we show that exonic coconversion can only explain diversity gradients near intron-exon boundaries if the conversion template comes from outside the population. In other words, there must be pervasive and ongoing horizontal gene transfer of self-splicing introns into extant fungal populations.
authors.affiliation: Molecular Systems Group, MRC London Institute of Medical Sciences (LMS) W12 0NN, United Kingdom.|Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, W12 0NN, United Kingdom.
authors.forename: Jelena
authors.initials: J
authors.lastname: Repar
authors.affiliation: Molecular Systems Group, MRC London Institute of Medical Sciences (LMS) W12 0NN, United Kingdom tobias.warnecke@imperial.ac.uk.|Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, W12 0NN, United Kingdom tobias.warnecke@imperial.ac.uk.
authors.forename: Tobias
authors.identifier: 0000-0002-4936-5428
authors.initials: T
authors.lastname: Warnecke
mesh_terms: D004720:Endonucleases / Q000235:genetics; D005785:Gene Conversion; D005800:Genes, Fungal; D007438:Introns; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D012641:Selection, Genetic; D015003:Yeasts / Q000235:genetics*
chemical_list: D004720:Endonucleases
keywords: gene conversion; genetic diversity; homing endonuclease; mutagenic; self-splicing introns