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      Evolutionary Origins and Dynamics of Octoploid Strawberry Subgenomes Revealed by Dense Targeted Capture Linkage Maps

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          Abstract

          Whole-genome duplications are radical evolutionary events that have driven speciation and adaptation in many taxa. Higher-order polyploids have complex histories often including interspecific hybridization and dynamic genomic changes. This chromosomal reshuffling is poorly understood for most polyploid species, despite their evolutionary and agricultural importance, due to the challenge of distinguishing homologous sequences from each other. Here, we use dense linkage maps generated with targeted sequence capture to improve the diploid strawberry ( Fragaria vesca) reference genome and to disentangle the subgenomes of the wild octoploid progenitors of cultivated strawberry, Fragaria virginiana and Fragaria chiloensis. Our novel approach, POLiMAPS (Phylogenetics Of Linkage-Map-Anchored Polyploid Subgenomes), leverages sequence reads to associate informative interhomeolog phylogenetic markers with linkage groups and reference genome positions. In contrast to a widely accepted model, we find that one of the four subgenomes originates with the diploid cytoplasm donor F. vesca, one with the diploid Fragaria iinumae, and two with an unknown ancestor close to F. iinumae. Extensive unidirectional introgression has converted F. iinumae-like subgenomes to be more F. vesca-like, but never the reverse, due either to homoploid hybridization in the F. iinumae-like diploid ancestors or else strong selection spreading F. vesca-like sequence among subgenomes through homeologous exchange. In addition, divergence between homeologous chromosomes has been substantially augmented by interchromosomal rearrangements. Our phylogenetic approach reveals novel aspects of the complicated web of genetic exchanges that occur during polyploid evolution and suggests a path forward for unraveling other agriculturally and ecologically important polyploid genomes.

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          How important are transposons for plant evolution?

          For decades, transposable elements have been known to produce a wide variety of changes in plant gene expression and function. This has led to the idea that transposable element activity has played a key part in adaptive plant evolution. This Review describes the kinds of changes that transposable elements can cause, discusses evidence that those changes have contributed to plant evolution and suggests future strategies for determining the extent to which these changes have in fact contributed to plant adaptation and evolution. Recent advances in genomics and phenomics for a range of plant species, particularly crops, have begun to allow the systematic assessment of these questions.
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            OneMap: software for genetic mapping in outcrossing species.

            OneMap is an environment for constructing linkage maps of outcrossing plant species, using full-sib families derived from two outbred parents. The analyses are performed using a novel methodology based on the maximum likelihood approach for simultaneous estimation of linkage and linkage phases (Wu et al. 2002), which has been successfully applied to sugarcane (Garcia et al. 2006). It is implemented as a set of functions for the freely distributed software R, and handles pairwise marker analysis, marker ordering and map refinement. The software is freely available at http://www.ciagri.usp.br/ approximately aafgarci/OneMap/.
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              Bidirectional interlocus concerted evolution following allopolyploid speciation in cotton (Gossypium).

              Polyploidy is a prominent process in plant evolution; yet few data address the question of whether homeologous sequences evolve independently subsequent to polyploidization. We report on ribosomal DNA (rDNA) evolution in five allopolyploid (AD genome) species of cotton (Gossypium) and species representing their diploid progenitors (A genome, D genome). Sequence data from the internal transcribed spacer regions (ITS1 and ITS2) and the 5.8S gene indicate that rDNA arrays are homogeneous, or nearly so, in all diploids and allopolyploids examined. Because these arrays occur at four chromosomal loci in allopolyploid cotton, two in each subgenome, repeats from different arrays must have become homogenized by interlocus concerted evolution. Southern hybridization analysis combined with copy-number estimation demonstrate that this process has gone to completion in the diploids and to completion or near-completion in all allopolyploid species and that it most likely involves the entire rDNA repeat. Phylogenetic analysis demonstrates that interlocus concerted evolution has been bidirectional in allopolyploid species--i.e., rDNA from four polyploid lineages has been homogenized to a D genome repeat type, whereas sequences from Gossypium mustelinum have concerted to an A genome repeat type. Although little is known regarding the functional significance of interlocus concerted evolution of homeologous sequences, this study demonstrates that the process occurs for tandemly repeated sequences in diploid and polyploid plants. That interlocus concerted evolution can occur bidirectionally subsequent to hybidization and polyploidization has significant implications for phylogeny reconstruction, especially when based on rDNA sequences.
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                Author and article information

                Journal
                Genome Biol Evol
                Genome Biol Evol
                gbe
                gbe
                Genome Biology and Evolution
                Oxford University Press
                1759-6653
                December 2014
                04 December 2014
                04 December 2014
                : 6
                : 12
                : 3295-3313
                Affiliations
                1Department of Integrative Biology, Oregon State University
                2Department of Biological Sciences, University of Pittsburgh
                3Department of Botany and Plant Pathology, Oregon State University
                Author notes
                *Corresponding author: E-mail: listona@ 123456science.oregonstate.edu .

                Associate editor: Yves Van De Peer

                Data deposition: Raw sequencing data have been deposited in the NCBI SRA ( http://www.ncbi.nlm.nih.gov/bioproject/263688). Phylogenetic trees are available in Treebase ( http://purl.org/phylo/treebase/phylows/study/TB2:S15849). Perl scripts are available in Github ( https://github.com/listonlab/POLiMAPS). New Fragaria genome assembly is available in Figshare ( http://dx.doi.org/10.6084/m9.figshare.1259206).

                Article
                evu261
                10.1093/gbe/evu261
                4986458
                25477420
                6dea6af0-6326-45b9-a05d-9c5d8ee5ad03
                © The Author(s) 2014. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 25 November 2014
                Page count
                Pages: 19
                Categories
                Research Article

                Genetics
                fragaria,polyploidy,phylogenetics,introgression,transposition,genome assembly
                Genetics
                fragaria, polyploidy, phylogenetics, introgression, transposition, genome assembly

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