title: Rate accelerations in nuclear 18S rDNA of mycoheterotrophic and parasitic angiosperms.
abstract: Rate variation in genes from all three genomes has been observed frequently in plant lineages with a parasitic and mycoheterotrophic mode of life. While the loss of photosynthetic ability leads to a relaxation of evolutionary constraints in genes involved in the photosynthetic apparatus, it remains to be determined how prevalent increased substitution rates are in nuclear DNA of non-photosynthetic angiosperms. In this study we infer rates of molecular evolution of 18S rDNA of all parasitic and mycoheterotorphic plant families (except Lauraceae and Polygalaceae) using relative rate tests. In several holoparasitic and mycoheterotrophic plant lineages extremely high substitution rates are observed compared to other photosynthetic angiosperms. The position and frequency of these substitutions have been identified to understand the mutation dynamics of 18S rRNA in achlorophyllous plants. Despite the presence of significantly elevated substitution rates, very few mutations occur in major functional and structural regions of the small ribosomal molecule, providing evidence that the efficiency of the translational apparatus in non-photosynthetic plants has not been affected.
authors.affiliation: Laboratory of Plant Systematics, Institute of Botany and Microbiology, K.U. Leuven, Kasteelpark Arenberg, Belgium. benny.lemaire@bio.kuleuven.be
authors.forename: Benny
authors.initials: B
authors.lastname: Lemaire
authors.forename: Suzy
authors.initials: S
authors.lastname: Huysmans
authors.forename: Erik
authors.initials: E
authors.lastname: Smets
authors.forename: Vincent
authors.initials: V
authors.lastname: Merckx
mesh_terms: D052818:Autotrophic Processes; D001482:Base Composition / Q000235:genetics; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry* / Q000235:genetics; D019143:Evolution, Molecular; D005658:Fungi / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D014644:Genetic Variation / Q000235:genetics; D016681:Genome, Fungal; D018745:Genome, Plant; D052836:Heterotrophic Processes; D019684:Magnoliopsida / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation; D038821:Mycorrhizae / Q000235:genetics / Q000502:physiology*; D010788:Photosynthesis / Q000235:genetics; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S