title: Repeat-induced point mutation and the population structure of transposable elements in Microbotryum violaceum.
abstract: Repeat-induced point mutation (RIP) is a genome defense in fungi that hypermutates repetitive DNA and is suggested to limit the accumulation of transposable elements. The genome of Microbotryum violaceum has a high density of transposable elements compared to other fungi, but there is also evidence of RIP activity. This is the first report of RIP in a basidiomycete and was obtained by sequencing multiple copies of the integrase gene of a copia-type transposable element and the helicase gene of a Helitron-type element. In M. violaceum, the targets for RIP mutations are the cytosine residues of TCG trinucleotide combinations. Although RIP is a linkage-dependent process that tends to increase the variation among repetitive sequences, a chromosome-specific substructuring was observed in the transposable element population. The observed chromosome-specific patterns are not consistent with RIP, but rather suggest an effect of gene conversion, which is also a linkage-dependent process but results in a homogenization of repeated sequences. Particular sequences were found more widely distributed within the genome than expected by chance and may reflect the recently active variants. Therefore, sequence variation of transposable elements in M. violaceum appears to be driven by selection for transposition ability in combination with the context-specific forces of the RIP and gene conversion.
authors.affiliation: Department of Biology, University of Virginia, Charlottesville, Virginia 22903, USA. michael.hood@virginia.edu
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hood
authors.forename: Melanie
authors.initials: M
authors.lastname: Katawczik
authors.forename: Tatiana
authors.initials: T
authors.lastname: Giraud
mesh_terms: D000704:Analysis of Variance; D001483:Base Sequence; D001487:Basidiomycota / Q000235:genetics*; D015825:Chromosomes, Fungal / Q000235:genetics; D016000:Cluster Analysis; D017931:DNA Primers; D004251:DNA Transposable Elements / Q000235:genetics*; D005785:Gene Conversion / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics; D005828:Genetics, Population; D008969:Molecular Sequence Data; D017354:Point Mutation / Q000235:genetics*; D017422:Sequence Analysis, DNA; D018911:Trinucleotide Repeats / Q000235:genetics*
chemical_list: D017931:DNA Primers; D004251:DNA Transposable Elements