title: Three divergent rDNA clusters predate the species divergence in Quercus petraea (Matt.) Liebl. and Quercus robur L.
abstract: Quercus petraea and Quercus robur are two closely related oak species that frequently hybridize. We sequenced 70 clones containing the 5.8S and ITS2 regions of ribosomal DNA (rDNA) from these two species and did not detect a species-specific difference. Surprisingly, three divergent (up to 12.6%) rDNA families were identified in both species, indicating that they predate the speciation event. Despite a large between-rDNA-families divergence, rDNA sequences were very similar within families, suggesting ongoing concerted evolution. Expression analysis, relative-rate tests, and mutation spectrum analyses indicated that only a single rDNA family is functional. We propose that past hybridization events, combined with nucleolar dominance, were the evolutionary processes underlying the contemporary rDNA variability in Q. petraea and Q. robur.
authors.affiliation: Department of Applied Plant Science, The Queen's University of Belfast, Belfast, N. Ireland.
authors.forename: G
authors.initials: G
authors.lastname: Muir
authors.forename: C C
authors.initials: CC
authors.lastname: Fleming
authors.forename: C
authors.initials: C
authors.lastname: Schlötterer
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017931:DNA Primers / Q000737:chemistry; D018744:DNA, Plant; D004275:DNA, Ribosomal; D014644:Genetic Variation / Q000235:genetics*; D008745:Methylation; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D011110:Polymorphism, Genetic; D011995:Recombination, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D014197:Trees / Q000235:genetics*
chemical_list: D017931:DNA Primers; D018744:DNA, Plant; D004275:DNA, Ribosomal