title: Ribosomal DNA variation, recombination and inheritance in the basidiomycete Trichaptum abietinum: implications for reticulate evolution.
abstract: Two divergent nuclear ribosomal DNA (nrDNA) types, designated alpha and beta, were found distributed in 11 North European populations of the basidiomycete Trichaptum abietinum. These types differed by a 220 bp indel in the internal transcribed spacer 1 (ITS1) sequence and a number of linked substitutions and small indel motives in the internal transcribed and intergenic spacers (ITS1, ITS2, IGS1 and IGS2). The alpha and beta haplotypes co-occurred in heterozygous somatic individuals (dikaryons) and segregated in a Mendelian fashion in monokaryotic single spore progenies. This result suggests that the haplotypes are encoded in different nuclei of field-collected dikaryons and inherited as a single locus. No meiotic recombinants were observed among the sequenced monokaryons. Population genetic analyses by PCR-RFLP revealed that a low frequency of evolutionary intermediate nrDNA types also existed in natural populations, presumably as a result of meiotic recombination of alpha and beta nrDNA. The existence of divergent nrDNA types in T. abietinum could be a result of a former independent evolution followed by a hybridization event. Phylogenetic analyses of ITS sequences suggest that the sister taxon T. fusco-violaceum has been involved in the evolutionary history of T. abietinum. Sequence polymorphisms observed in the translation elongation factor 1alpha (efa) and glyceraldehyde-3-phosphate dehydrogenase (gpd) genes, did not reveal two well-defined types of these genes. The results are discussed in the light of other evolutionary mechanisms as well.
authors.affiliation: Division of Botany and Plant Physiology, Department of Biology, University of Oslo, PO Box 1045, Blindern, N-0316 Oslo, Norway. haavarka@bio.uio.no
authors.forename: H
authors.initials: H
authors.lastname: Kauserud
authors.forename: T
authors.initials: T
authors.lastname: Schumacher
mesh_terms: D004271:DNA, Fungal / Q000235:genetics*; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D005060:Europe; D019143:Evolution, Molecular; D014644:Genetic Variation; D005843:Geography; D006239:Haplotypes; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011124:Polyporaceae / Q000145:classification / Q000235:genetics*; D011995:Recombination, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer