title: Ginkgo and Welwitschia Mitogenomes Reveal Extreme Contrasts in Gymnosperm Mitochondrial Evolution.
abstract: Mitochondrial genomes (mitogenomes) of flowering plants are well known for their extreme diversity in size, structure, gene content, and rates of sequence evolution and recombination. In contrast, little is known about mitogenomic diversity and evolution within gymnosperms. Only a single complete genome sequence is available, from the cycad Cycas taitungensis, while limited information is available for the one draft sequence, from Norway spruce (Picea abies). To examine mitogenomic evolution in gymnosperms, we generated complete genome sequences for the ginkgo tree (Ginkgo biloba) and a gnetophyte (Welwitschia mirabilis). There is great disparity in size, sequence conservation, levels of shared DNA, and functional content among gymnosperm mitogenomes. The Cycas and Ginkgo mitogenomes are relatively small, have low substitution rates, and possess numerous genes, introns, and edit sites; we infer that these properties were present in the ancestral seed plant. By contrast, the Welwitschia mitogenome has an expanded size coupled with accelerated substitution rates and extensive loss of these functional features. The Picea genome has expanded further, to more than 4 Mb. With regard to structural evolution, the Cycas and Ginkgo mitogenomes share a remarkable amount of intergenic DNA, which may be related to the limited recombinational activity detected at repeats in Ginkgo Conversely, the Welwitschia mitogenome shares almost no intergenic DNA with any other seed plant. By conducting the first measurements of rates of DNA turnover in seed plant mitogenomes, we discovered that turnover rates vary by orders of magnitude among species.
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln School of Biological Sciences, University of Nebraska, Lincoln ACGT, INC., Wheeling, IL.
authors.forename: Wenhu
authors.initials: W
authors.lastname: Guo
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln Department of Agronomy and Horticulture, University of Nebraska, Lincoln The Field Museum of Natural History, Chicago, IL IZMB-Institut Für Zelluläre Und Molekulare Botanik, Abteilung Molekulare Evolution, Universität Bonn, Kirschallee 1, Bonn 53115, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Grewe
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln Department of Agronomy and Horticulture, University of Nebraska, Lincoln.
authors.forename: Weishu
authors.initials: W
authors.lastname: Fan
authors.affiliation: Department of Biology, Indiana University, Bloomington DuPont Pioneer, Wilmington, DE.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Young
authors.affiliation: IZMB-Institut Für Zelluläre Und Molekulare Botanik, Abteilung Molekulare Evolution, Universität Bonn, Kirschallee 1, Bonn 53115, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Knoop
authors.affiliation: Department of Biology, Indiana University, Bloomington.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Palmer
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln Department of Agronomy and Horticulture, University of Nebraska, Lincoln jpmower@unl.edu.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Mower
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D017343:Genes, Plant; D054629:Genome, Mitochondrial; D018745:Genome, Plant; D020441:Ginkgo biloba / Q000235:genetics*; D035682:Gnetophyta / Q000235:genetics*; D008928:Mitochondria / Q000235:genetics*; D010802:Phylogeny; D017393:RNA Editing
keywords: DNA turnover; Ginkgo biloba; RNA editing; Welwitschia mirabilis; mitochondrial genomes; substitution rates