Ribosomal DNA variation, recombination and inheritance in the basidiomycete Trichaptum abietinum: implications for reticulate evolution.
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.
Kauserud
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Division of Botany and Plant Physiology, Department of Biology, University of Oslo, PO Box 1045, Blindern, N-0316 Oslo, Norway. haavarka@bio.uio.no
Schumacher
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T
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
D004271:DNA, Fungal; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer