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Matyášek R, Kalfusová R, Kuderová A, Řehůřková K, Sochorová J, Kovařík A. Transcriptional Silencing of 35S rDNA in Tragopogon porrifolius Correlates with Cytosine Methylation in Sequence-Specific Manner. Int J Mol Sci 2024; 25:7540. [PMID: 39062783 PMCID: PMC11276851 DOI: 10.3390/ijms25147540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2024] [Revised: 06/21/2024] [Accepted: 07/04/2024] [Indexed: 07/28/2024] Open
Abstract
Despite the widely accepted involvement of DNA methylation in the regulation of rDNA transcription, the relative participation of different cytosine methylation pathways is currently described only for a few model plants. Using PacBio, Bisulfite, and RNA sequencing; PCR; Southern hybridizations; and FISH, the epigenetic consequences of rDNA copy number variation were estimated in two T. porrifolius lineages, por1 and por2, the latter with more than twice the rDNA copy numbers distributed approximately equally between NORs on chromosomes A and D. The lower rDNA content in por1 correlated with significantly reduced (>90%) sizes of both D-NORs. Moreover, two (L and S) prominent rDNA variants, differing in the repetitive organization of intergenic spacers, were detected in por2, while only the S-rDNA variant was detected in por1. Transcriptional activity of S-rDNA in por1 was associated with secondary constriction of both A-NORs. In contrast, silencing of S-rDNA in por2 was accompanied by condensation of A-NORs, secondary constriction on D-NORs, and L-rDNA transcriptional activity, suggesting (i) bidirectional nucleolar dominance and (ii) association of S-rDNAs with A-NORs and L-rDNAs with D-NORs in T. porrifolius. Each S- and L-rDNA array was formed of several sub-variants differentiating both genetically (specific SNPs) and epigenetically (transcriptional efficiency and cytosine methylation). The most significant correlations between rDNA silencing and methylation were detected for symmetric CWG motifs followed by CG motifs. No correlations were detected for external cytosine in CCGs or asymmetric CHHs, where methylation was rather position-dependent, particularly for AT-rich variants. We conclude that variations in rDNA copy numbers in plant diploids can be accompanied by prompt epigenetic responses to maintain an appropriate number of active rDNAs. The methylation dynamics of CWGs are likely to be the most responsible for regulating silent and active rDNA states.
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Affiliation(s)
- Roman Matyášek
- Institute of Biophysics of the Czech Academy of Sciences, 612 65 Brno, Czech Republic; (R.K.); (A.K.); (K.Ř.); (J.S.); (A.K.)
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Mahelka V, Kopecký D, Majka J, Krak K. Uniparental expression of ribosomal RNA in × Festulolium grasses: a link between the genome and nucleolar dominance. FRONTIERS IN PLANT SCIENCE 2023; 14:1276252. [PMID: 37790792 PMCID: PMC10544908 DOI: 10.3389/fpls.2023.1276252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 08/30/2023] [Indexed: 10/05/2023]
Abstract
Genome or genomic dominance (GD) is a phenomenon observed in hybrids when one parental genome becomes dominant over the other. It is manifested by the replacement of chromatin of the submissive genome by that of the dominant genome and by biased gene expression. Nucleolar dominance (ND) - the functional expression of only one parental set of ribosomal genes in hybrids - is another example of an intragenomic competitive process which, however, concerns ribosomal DNA only. Although GD and ND are relatively well understood, the nature and extent of their potential interdependence is mostly unknown. Here, we ask whether hybrids showing GD also exhibit ND and, if so, whether the dominant genome is the same. To test this, we used hybrids between Festuca and Lolium grasses (Festulolium), and between two Festuca species in which GD has been observed (with Lolium as the dominant genome in Festulolium and F. pratensis in interspecific Festuca hybrids). Using amplicon sequencing of ITS1 and ITS2 of the 45S ribosomal DNA (rDNA) cluster and molecular cytogenetics, we studied the organization and expression of rDNA in leaf tissue in five hybrid combinations, four generations and 31 genotypes [F. pratensis × L. multiflorum (F1, F2, F3, BC1), L. multiflorum × F. pratensis (F1), L. multiflorum × F. glaucescens (F2), L. perenne × F. pratensis (F1), F. glaucescens × F. pratensis (F1)]. We have found that instant ND occurs in Festulolium, where expression of Lolium-type rDNA reached nearly 100% in all F1 hybrids and was maintained through subsequent generations. Therefore, ND and GD in Festulolium are manifested by the same dominant genome (Lolium). We also confirmed the concordance between GD and ND in an interspecific cross between two Festuca species.
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Affiliation(s)
- Václav Mahelka
- Czech Academy of Sciences, Institute of Botany, Průhonice, Czechia
| | - David Kopecký
- Institute of Experimental Botany of the Czech Academy of Sciences, Centre of Plant Structural and Functional Genomics, Olomouc, Czechia
| | - Joanna Majka
- Institute of Experimental Botany of the Czech Academy of Sciences, Centre of Plant Structural and Functional Genomics, Olomouc, Czechia
| | - Karol Krak
- Czech Academy of Sciences, Institute of Botany, Průhonice, Czechia
- Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Prague, Czechia
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Borowska-Zuchowska N, Mykhailyk S, Robaszkiewicz E, Matysiak N, Mielanczyk L, Wojnicz R, Kovarik A, Hasterok R. Switch them off or not: selective rRNA gene repression in grasses. TRENDS IN PLANT SCIENCE 2023; 28:661-672. [PMID: 36764871 DOI: 10.1016/j.tplants.2023.01.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 12/31/2022] [Accepted: 01/11/2023] [Indexed: 05/13/2023]
Abstract
Nucleolar dominance (ND) is selective epigenetic silencing of 35-48S rDNA loci. In allopolyploids, it is frequently manifested at the cytogenetic level by the inactivation of nucleolar organiser region(s) (NORs) inherited from one or several evolutionary ancestors. Grasses are ecologically and economically one of the most important land plant groups, which have frequently evolved through hybridisation and polyploidisation events. Here we review common and unique features of ND phenomena in this monocot family from cytogenetic, molecular, and genomic perspectives. We highlight recent advances achieved by using an allotetraploid model grass, Brachypodium hybridum, where ND commonly occurs at a population level, and we cover modern genomic approaches that decipher structural features of core arrays of NORs.
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Affiliation(s)
- Natalia Borowska-Zuchowska
- Plant Cytogenetics and Molecular Biology Group, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, Katowice 40-032, Poland.
| | - Serhii Mykhailyk
- Plant Cytogenetics and Molecular Biology Group, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, Katowice 40-032, Poland
| | - Ewa Robaszkiewicz
- Plant Cytogenetics and Molecular Biology Group, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, Katowice 40-032, Poland
| | - Natalia Matysiak
- Department of Histology and Cell Pathology, the Medical University of Silesia in Katowice, School of Medicine with the Division of Dentistry, Zabrze, Poland
| | - Lukasz Mielanczyk
- Department of Histology and Cell Pathology, the Medical University of Silesia in Katowice, School of Medicine with the Division of Dentistry, Zabrze, Poland; Silesian Nanomicroscopy Centre in Zabrze, Silesia LabMed - Research and Implementation Centre, Medical University of Silesia, Katowice, Poland
| | - Romuald Wojnicz
- Department of Histology and Cell Pathology, the Medical University of Silesia in Katowice, School of Medicine with the Division of Dentistry, Zabrze, Poland; Silesian Nanomicroscopy Centre in Zabrze, Silesia LabMed - Research and Implementation Centre, Medical University of Silesia, Katowice, Poland
| | - Ales Kovarik
- Department of Molecular Epigenetics, Institute of Biophysics, Czech Academy of Sciences, CZ-61200 Brno, Czech Republic
| | - Robert Hasterok
- Plant Cytogenetics and Molecular Biology Group, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, Katowice 40-032, Poland.
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Joshi P, Ansari H, Dickson R, Ellison NW, Skema C, Tate JA. Polyploidy on islands - concerted evolution and gene loss amid chromosomal stasis. ANNALS OF BOTANY 2023; 131:33-44. [PMID: 35390127 PMCID: PMC9904340 DOI: 10.1093/aob/mcac051] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Accepted: 04/04/2022] [Indexed: 05/25/2023]
Abstract
BACKGROUND AND AIMS Polyploidy is an important process that often generates genomic diversity within lineages, but it can also cause changes that result in loss of genomic material. Island lineages, while often polyploid, typically show chromosomal stasis but have not been investigated in detail regarding smaller-scale gene loss. Our aim was to investigate post-polyploidization genome dynamics in a chromosomally stable lineage of Malvaceae endemic to New Zealand. METHODS We determined chromosome numbers and used fluorescence in situ hybridization to localize 18S and 5S rDNA. Gene sequencing of 18S rDNA, the internal transcribed spacers (ITS) with intervening 5.8S rDNA, and a low-copy nuclear gene, GBSSI-1, was undertaken to determine if gene loss occurred in the New Zealand lineage following polyploidy. KEY RESULTS The chromosome number for all species investigated was 2n = 42, with the first published report for the monotypic Australian genus Asterotrichion. The five species investigated all had two 5S rDNA signals localized interstitially on the long arm of one of the largest chromosome pairs. All species, except Plagianthus regius, had two 18S rDNA signals localized proximally on the short arm of one of the smallest chromosome pairs. Plagianthus regius had two additional 18S rDNA signals on a separate chromosome, giving a total of four. Sequencing of nuclear ribosomal 18S rDNA and the ITS cistron indicated loss of historical ribosomal repeats. Phylogenetic analysis of a low-copy nuclear gene, GBSSI-1, indicated that some lineages maintained three copies of the locus, while others have lost one or two copies. CONCLUSIONS Although island endemic lineages show chromosomal stasis, with no additional changes in chromosome number, they may undergo smaller-scale processes of gene loss and concerted evolution ultimately leading to further genome restructuring and downsizing.
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Affiliation(s)
- Prashant Joshi
- School of Natural Sciences, Massey University, Palmerston North, New Zealand
| | - Helal Ansari
- AgResearch Grasslands Research Centre, Palmerston North, New Zealand
| | - Rowan Dickson
- School of Natural Sciences, Massey University, Palmerston North, New Zealand
| | | | - Cynthia Skema
- School of Natural Sciences, Massey University, Palmerston North, New Zealand
- Morris Arboretum of the University of Pennsylvania, Philadelphia, PA, USA
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Tynkevich YO, Novikov AV, Chorney II, Volkov RA. Organization of the 5S rDNA Intergenic Spacer and Its Use in the Molecular Taxonomy of the Genus Aconitum L. CYTOL GENET+ 2022. [DOI: 10.3103/s0095452722060111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Eriksson MC, Mandáková T, McCann J, Temsch EM, Chase MW, Hedrén M, Weiss-Schneeweiss H, Paun O. Repeat dynamics across timescales: a perspective from sibling allotetraploid marsh orchids (Dactylorhiza majalis s.l.). Mol Biol Evol 2022; 39:6651906. [PMID: 35904928 PMCID: PMC9366187 DOI: 10.1093/molbev/msac167] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
To provide insights into the fate of transposable elements (TEs) across timescales in a post-polyploidization context, we comparatively investigate five sibling Dactylorhiza allotetraploids (Orchidaceae) formed independently and sequentially between 500 and 100K generations ago by unidirectional hybridization between diploids D. fuchsii and D. incarnata. Our results first reveal that the paternal D. incarnata genome shows a marked increased content of LTR retrotransposons compared to the maternal species, reflected in its larger genome size and consistent with a previously hypothesized bottleneck. With regard to the allopolyploids, in the youngest D. purpurella both genome size and TE composition appear to be largely additive with respect to parents, whereas for polyploids of intermediate ages we uncover rampant genome expansion on a magnitude of multiple entire genomes of some plants such as Arabidopsis. The oldest allopolyploids in the series are not larger than the intermediate ones. A putative tandem repeat, potentially derived from a non-autonomous miniature inverted-repeat TE (MITE) drives much of the genome dynamics in the allopolyploids. The highly dynamic MITE-like element is found in higher proportions in the maternal diploid, D. fuchsii, but is observed to increase in copy number in both subgenomes of the allopolyploids. Altogether, the fate of repeats appears strongly regulated and therefore predictable across multiple independent allopolyploidization events in this system. Apart from the MITE-like element, we consistently document a mild genomic shock following the allopolyploidizations investigated here, which may be linked to their relatively large genome sizes, possibly associated with strong selection against further genome expansions.
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Affiliation(s)
- Mimmi C Eriksson
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, A-1030 Vienna, Austria.,Vienna Graduate School of Population Genetics, Veterinärplatz 1, A-1210 Vienna, Austria
| | - Terezie Mandáková
- Plant Cytogenomics Research Group, CEITEC-Central - European Institute of Technology, Masaryk University, Brno 62500, Czech Republic
| | - Jamie McCann
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
| | - Eva M Temsch
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
| | - Mark W Chase
- Royal Botanic Gardens Kew, London TW9 3AE, United Kingdom.,Department of Environment and Agriculture, Curtin University, Perth, Western Australia, Australia
| | - Mikael Hedrén
- Department of Biology, University of Lund, Sölvegatan 37, SE-223 62 Lund, Sweden
| | - Hanna Weiss-Schneeweiss
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
| | - Ovidiu Paun
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
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Krak K, Caklová P, Kopecký D, Blattner FR, Mahelka V. Horizontally Acquired nrDNAs Persist in Low Amounts in Host Hordeum Genomes and Evolve Independently of Native nrDNA. FRONTIERS IN PLANT SCIENCE 2021; 12:672879. [PMID: 34079572 PMCID: PMC8165317 DOI: 10.3389/fpls.2021.672879] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Accepted: 04/22/2021] [Indexed: 06/12/2023]
Abstract
Nuclear ribosomal DNA (nrDNA) has displayed extraordinary dynamics during the evolution of plant species. However, the patterns and evolutionary significance of nrDNA array expansion or contraction are still relatively unknown. Moreover, only little is known of the fate of minority nrDNA copies acquired between species via horizontal transfer. The barley genus Hordeum (Poaceae) represents a good model for such a study, as species of section Stenostachys acquired nrDNA via horizontal transfer from at least five different panicoid genera, causing long-term co-existence of native (Hordeum-like) and non-native (panicoid) nrDNAs. Using quantitative PCR, we investigated copy number variation (CNV) of nrDNA in the diploid representatives of the genus Hordeum. We estimated the copy number of the foreign, as well as of the native ITS types (ribotypes), and followed the pattern of their CNV in relation to the genus' phylogeny, species' genomes size and the number of nrDNA loci. For the native ribotype, we encountered an almost 19-fold variation in the mean copy number among the taxa analysed, ranging from 1689 copies (per 2C content) in H. patagonicum subsp. mustersii to 31342 copies in H. murinum subsp. glaucum. The copy numbers did not correlate with any of the genus' phylogeny, the species' genome size or the number of nrDNA loci. The CNV was high within the recognised groups (up to 13.2 × in the American I-genome species) as well as between accessions of the same species (up to 4×). Foreign ribotypes represent only a small fraction of the total number of nrDNA copies. Their copy numbers ranged from single units to tens and rarely hundreds of copies. They amounted, on average, to between 0.1% (Setaria ribotype) and 1.9% (Euclasta ribotype) of total nrDNA. None of the foreign ribotypes showed significant differences with respect to phylogenetic groups recognised within the sect. Stenostachys. Overall, no correlation was found between copy numbers of native and foreign nrDNAs suggesting the sequestration and independent evolution of native and non-native nrDNA arrays. Therefore, foreign nrDNA in Hordeum likely poses a dead-end by-product of horizontal gene transfer events.
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Affiliation(s)
- Karol Krak
- Czech Academy of Sciences, Institute of Botany, Prùhonice, Czechia
- Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Prague 6, Czechia
| | - Petra Caklová
- Czech Academy of Sciences, Institute of Botany, Prùhonice, Czechia
| | - David Kopecký
- Czech Academy of Sciences, Institute of Experimental Botany, Centre of the Region Haná for Biotechnological and Agricultural Research, Olomouc, Czechia
| | - Frank R. Blattner
- Experimental Taxonomy, Leibniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany
- German Centre of Integrative Biodiversity Research (iDiv) Halle–Jena–Leipzig, Leipzig, Germany
| | - Václav Mahelka
- Czech Academy of Sciences, Institute of Botany, Prùhonice, Czechia
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Dou Q, Liu R, Yu F. Chromosomal organization of repetitive DNAs in Hordeum bogdanii and H. brevisubulatum (Poaceae). COMPARATIVE CYTOGENETICS 2016; 10:465-481. [PMID: 28123672 PMCID: PMC5240503 DOI: 10.3897/compcytogen.v10i4.9666] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 08/12/2016] [Indexed: 05/29/2023]
Abstract
Molecular karyotypes of Hordeum bogdanii Wilensky, 1918 (2n = 14), and Hordeum brevisubulatum Link, 1844 ssp. brevisubulatum (2n = 28), were characterized by physical mapping of several repetitive sequences. A total of 18 repeats, including all possible di- or trinucleotide SSR (simple sequence repeat) motifs and satellite DNAs, such as pAs1, 5S rDNA, 45S rDNA, and pSc119.2, were used as probes for fluorescence in situ hybridization on root-tip metaphase chromosomes. Except for the SSR motifs AG, AT and GC, all the repeats we examined produced detectable hybridization signals on chromosomes of both species. A detailed molecular karyotype of the I genome of Hordeum bogdanii is described for the first time, and each repetitive sequence is physically mapped. A high degree of chromosome variation, including aneuploidy and structural changes, was observed in Hordeum brevisubulatum. Although the distribution of repeats in the chromosomes of Hordeum brevisubulatum is different from that of Hordeum bogdanii, similar patterns between the two species imply that the autopolyploid origin of Hordeum brevisubulatum is from a Hordeum species with an I genome. A comparison of the I genome and the other Hordeum genomes, H, Xa and Xu, shows that colocalization of motifs AAC, ACT and CAT and colocalization of motifs AAG and AGG are characteristic of the I genome. In addition, we discuss the evolutionary significance of repeats in the genome during genome differentiation.
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Affiliation(s)
- Quanwen Dou
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810001, China
| | - Ruijuan Liu
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810001, China
| | - Feng Yu
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810001, China
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Matyášek R, Dobešová E, Húska D, Ježková I, Soltis PS, Soltis DE, Kovařík A. Interpopulation hybridization generates meiotically stable rDNA epigenetic variants in allotetraploid Tragopogon mirus. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2016; 85:362-377. [PMID: 26711705 DOI: 10.1111/tpj.13110] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Revised: 12/08/2015] [Accepted: 12/10/2015] [Indexed: 06/05/2023]
Abstract
Uniparental silencing of 35S rRNA genes (rDNA), known as nucleolar dominance (ND), is common in interspecific hybrids. Allotetraploid Tragopogon mirus composed of Tragopogon dubius (d) and Tragopogon porrifolius (p) genomes shows highly variable ND. To examine the molecular basis of such variation, we studied the genetic and epigenetic features of rDNA homeologs in several lines derived from recently and independently formed natural populations. Inbred lines derived from T. mirus with a dominant d-rDNA homeolog transmitted this expression pattern over generations, which may explain why it is prevalent among natural populations. In contrast, lines derived from the p-rDNA dominant progenitor were meiotically unstable, frequently switching to co-dominance. Interpopulation crosses between progenitors displaying reciprocal ND resulted in d-rDNA dominance, indicating immediate suppression of p-homeologs in F1 hybrids. Original p-rDNA dominance was not restored in later generations, even in those segregants that inherited the corresponding parental rDNA genotype, thus indicating the generation of additional p-rDNA and d-rDNA epigenetic variants. Despite preserved intergenic spacer (IGS) structure, they showed altered cytosine methylation and chromatin condensation patterns, and a correlation between expression, hypomethylation of RNA Pol I promoters and chromatin decondensation was apparent. Reversion of such epigenetic variants occurred rarely, resulting in co-dominance maintained in individuals with distinct genotypes. Generally, interpopulation crosses may generate epialleles that are not present in natural populations, underlying epigenetic dynamics in young allopolyploids. We hypothesize that highly expressed variants with distinct IGS features may induce heritable epigenetic reprogramming of the partner rDNA arrays, harmonizing the expression of thousands of genes in allopolyploids.
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Affiliation(s)
- Roman Matyášek
- Laboratory of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Brno, Czech Republic
| | - Eva Dobešová
- Laboratory of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Brno, Czech Republic
| | - Dalibor Húska
- Laboratory of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Brno, Czech Republic
| | - Ivana Ježková
- Laboratory of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Brno, Czech Republic
| | - Pamela S Soltis
- Florida Museum of National History, University of Florida, Gainesville, FL, 32611, USA
| | - Douglas E Soltis
- Florida Museum of National History, University of Florida, Gainesville, FL, 32611, USA
- Department of Biology, University of Florida, Gainesville, FL, 32611, USA
| | - Aleš Kovařík
- Laboratory of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Brno, Czech Republic
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Xu J, Xu Y, Yonezawa T, Li L, Hasegawa M, Lu F, Chen J, Zhang W. Polymorphism and evolution of ribosomal DNA in tea (Camellia sinensis, Theaceae). Mol Phylogenet Evol 2015; 89:63-72. [DOI: 10.1016/j.ympev.2015.03.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Revised: 03/22/2015] [Accepted: 03/25/2015] [Indexed: 01/18/2023]
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Silenced rRNA genes are activated and substitute for partially eliminated active homeologs in the recently formed allotetraploid, Tragopogon mirus (Asteraceae). Heredity (Edinb) 2014; 114:356-65. [PMID: 25537492 DOI: 10.1038/hdy.2014.111] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 11/04/2014] [Accepted: 11/05/2014] [Indexed: 11/08/2022] Open
Abstract
To study the relationship between uniparental rDNA (encoding 18S, 5.8S and 26S ribosomal RNA) silencing (nucleolar dominance) and rRNA gene dosage, we studied a recently emerged (within the last 80 years) allotetraploid Tragopogon mirus (2n=24), formed from the diploid progenitors T. dubius (2n=12, D-genome donor) and T. porrifolius (2n=12, P-genome donor). Here, we used molecular, cytogenetic and genomic approaches to analyse rRNA gene activity in two sibling T. mirus plants (33A and 33B) with widely different rRNA gene dosages. Plant 33B had ~400 rRNA genes at the D-genome locus, which is typical for T. mirus, accounting for ~25% of total rDNA. We observed characteristic expression dominance of T. dubius-origin genes in all organs. Its sister plant 33A harboured a homozygous macrodeletion that reduced the number of T. dubius-origin genes to about 70 copies (~4% of total rDNA). It showed biparental rDNA expression in root, flower and callus, but not in leaf where D-genome rDNA dominance was maintained. There was upregulation of minor rDNA variants in some tissues. The RNA polymerase I promoters of reactivated T. porrifolius-origin rRNA genes showed reduced DNA methylation, mainly at symmetrical CG and CHG nucleotide motifs. We hypothesise that active, decondensed rDNA units are most likely to be deleted via recombination. The silenced homeologs could be used as a 'first reserve' to ameliorate mutational damage and contribute to evolutionary success of polyploids. Deletion and reactivation cycles may lead to bidirectional homogenisation of rRNA arrays in the long term.
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Zozomová-Lihová J, Mandáková T, Kovaříková A, Mühlhausen A, Mummenhoff K, Lysak MA, Kovařík A. When fathers are instant losers: homogenization of rDNA loci in recently formed Cardamine × schulzii trigenomic allopolyploid. THE NEW PHYTOLOGIST 2014; 203:1096-1108. [PMID: 24916080 DOI: 10.1111/nph.12873] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Accepted: 04/29/2014] [Indexed: 05/20/2023]
Abstract
Recently formed allopolyploids represent an excellent system to study the impacts of hybridization and genomic duplication on genome structure and evolution. Here we explored the 35SrRNA genes (rDNA) in the Cardamine × schulzii allohexaploid that was formed by two subsequent hybridization events within the past c. 150 yr. The rDNA loci were analyzed by cloning, next generation sequencing (NGS), RT-PCR and FISH methods. The primary C. × insueta triploid hybrid derived from C. rivularis (♀) and C. amara (♂) had gene ratios highly skewed towards maternal sequences. Similarly, C. × schulzii, originating from the secondary hybridization event involving C. × insueta (♀) and C. pratensis (♂), showed a reduction in paternal rDNA homeologs despite an excess of chromosomes inherited from C. pratensis. We also identified novel rDNA loci in C. × schulzii, suggesting that lost loci might be slowly reinstalled by translocation (but not recombination) of genes from partner genomes. Prevalent clonal propagation of allopolyploids, C. × insueta and C. × schulzii, indicates that concerted evolution of rDNA may occur in the absence of extensive meiotic cycles. Adoption of NGS in rDNA variant analysis is highly informative for deciphering the evolutionary histories of allopolyploid species with ongoing homogenization processes.
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Affiliation(s)
| | - Terezie Mandáková
- RG Plant Cytogenomics, CEITEC, Masaryk University, Brno, Czech Republic
| | - Alena Kovaříková
- Department of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno, Czech Republic
| | | | - Klaus Mummenhoff
- Department of Biology, University Osnabrueck, Osnabrueck, Germany
| | - Martin A Lysak
- RG Plant Cytogenomics, CEITEC, Masaryk University, Brno, Czech Republic
| | - Aleš Kovařík
- Department of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno, Czech Republic
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13
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Sehrish T, Symonds VV, Soltis DE, Soltis PS, Tate JA. Gene silencing via DNA methylation in naturally occurring Tragopogon miscellus (Asteraceae) allopolyploids. BMC Genomics 2014; 15:701. [PMID: 25145399 PMCID: PMC4148530 DOI: 10.1186/1471-2164-15-701] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Accepted: 08/18/2014] [Indexed: 01/03/2023] Open
Abstract
Background Hybridization coupled with whole-genome duplication (allopolyploidy) leads to a variety of genetic and epigenetic modifications in the resultant merged genomes. In particular, gene loss and gene silencing are commonly observed post-polyploidization. Here, we investigated DNA methylation as a potential mechanism for gene silencing in Tragopogon miscellus (Asteraceae), a recent and recurrently formed allopolyploid. This species, which also exhibits extensive gene loss, was formed from the diploids T. dubius and T. pratensis. Results Comparative bisulfite sequencing revealed CG methylation of parental homeologs for three loci (S2, S18 and TDF-44) that were previously identified as silenced in T. miscellus individuals relative to the diploid progenitors. One other locus (S3) examined did not show methylation, indicating that other transcriptional and post-transcriptional mechanisms are likely responsible for silencing that homeologous locus. Conclusions These results indicate that Tragopogon miscellus allopolyploids employ diverse mechanisms, including DNA methylation, to respond to the potential shock of genome merger and doubling. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-701) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | | | - Jennifer A Tate
- Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
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14
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Bočkor VV, Barišić D, Horvat T, Maglica Ž, Vojta A, Zoldoš V. Inhibition of DNA methylation alters chromatin organization, nuclear positioning and activity of 45S rDNA loci in cycling cells of Q. robur. PLoS One 2014; 9:e103954. [PMID: 25093501 PMCID: PMC4122370 DOI: 10.1371/journal.pone.0103954] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Accepted: 07/03/2014] [Indexed: 12/04/2022] Open
Abstract
Around 2200 copies of genes encoding ribosomal RNA (rRNA) in pedunculate oak, Quercus robur, are organized into two rDNA loci, the major (NOR-1) and the minor (NOR-2) locus. We present the first cytogenetic evidence indicating that the NOR-1 represents the active nucleolar organizer responsible for rRNA synthesis, while the NOR-2 probably stays transcriptionally silent and does not participate in the formation of the nucleolus in Q. robur, which is a situation resembling the well-known phenomenon of nucleolar dominance. rDNA chromatin topology analyses in cycling root tip cells by light and electron microscopy revealed the minor locus to be highly condensed and located away from the nucleolus, while the major locus was consistently associated with the nucleolus and often exhibited different levels of condensation. In addition, silver precipitation was confined exclusively to the NOR-1 locus. Also, NOR-2 was highly methylated at cytosines and rDNA chromatin was marked with histone modifications characteristic for repressive state. After treatment of the root cells with the methylation inhibitor 5-aza-2′-deoxycytidine, we observed an increase in the total level of rRNA transcripts and a decrease in DNA methylation level at the NOR-2 locus. Also, NOR-2 sites relocalized with respect to the nuclear periphery/nucleolus, however, the relocation did not affect the contribution of this locus to nucleolar formation, nor did it affect rDNA chromatin decondensation, strongly suggesting that NOR-2 has lost the function of rRNA synthesis and nucleolar organization.
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Affiliation(s)
- Vedrana Vičić Bočkor
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
| | - Darko Barišić
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Tomislav Horvat
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
| | - Željka Maglica
- Ecole Polytechnique Fédéral de Lausanne, Lausanne, Switzerland
| | - Aleksandar Vojta
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
| | - Vlatka Zoldoš
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
- * E-mail:
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15
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Fan X, Liu J, Sha LN, Sun GL, Hu ZQ, Zeng J, Kang HY, Zhang HQ, Wang Y, Wang XL, Zhang L, Ding CB, Yang RW, Zheng YL, Zhou YH. Evolutionary pattern of rDNA following polyploidy in Leymus (Triticeae: Poaceae). Mol Phylogenet Evol 2014; 77:296-306. [PMID: 24780748 DOI: 10.1016/j.ympev.2014.04.016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 03/20/2014] [Accepted: 04/16/2014] [Indexed: 11/26/2022]
Abstract
Ribosomal ITS polymorphism and its ancestral genome origin of polyploid Leymus were examined to infer the evolutionary outcome of rDNA gene following allopolyploid speciation and to elucidate the geographic pattern of ITS variation. The results demonstrated that different polyploids have experienced varying fates, including maintenance or homogenization of divergent arrays, occurrence of chimeric repeats and potential pseudogenes. Our data suggested that (1) the Ns, P/F, and St genomic types in Leymus were originated from Psathyrostachys, Agropyron/Eremopyrum, and Pseudoroegneria, respectively; (2) the occurrence of a higher proportion of Leymus species with predominant uniparental rDNA type might associate with the segmental allopolyploid origin, nucleolar dominance of alloploids, and rapid radiation of Leymus; (3) maintenance of multiple parental ITS types in allopolyploid might result from long generation times associated to vegetative multiplication, number and chromosomal location of ribosomal loci and/or recurrent hybridization; (4) the rDNA genealogical structure of Leymus species might associate with the geographic origins; and (5) ITS sequence clade shared by Leymus species from Central Asia, North America, and Nordic might be an outcome of ancestral ITS homogenization. Our results shed new light on understanding evolutionary outcomes of rDNA following allopolyploid speciation and geographic isolation.
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Affiliation(s)
- Xing Fan
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China; Key Laboratory of Crop Genetic Resources and Improvement, Ministry of Education, Sichuan Agricultural University, Yaan 625014, Sichuan, China
| | - Jing Liu
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China
| | - Li-Na Sha
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China
| | - Gen-Lou Sun
- Biology Department, Saint Mary's University, Halifax NS B3H 3C3, Canada
| | - Zhi-Qin Hu
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China
| | - Jian Zeng
- College of Resources and Environment, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China
| | - Hou-Yang Kang
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China
| | - Hai-Qin Zhang
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China
| | - Yi Wang
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China
| | - Xiao-Li Wang
- College of Life Sciences, Sichuan Agricultural University, Yaan 625014, Sichuan, China
| | - Li Zhang
- College of Life Sciences, Sichuan Agricultural University, Yaan 625014, Sichuan, China
| | - Chun-Bang Ding
- College of Life Sciences, Sichuan Agricultural University, Yaan 625014, Sichuan, China
| | - Rui-Wu Yang
- College of Life Sciences, Sichuan Agricultural University, Yaan 625014, Sichuan, China
| | - You-Liang Zheng
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China; Key Laboratory of Crop Genetic Resources and Improvement, Ministry of Education, Sichuan Agricultural University, Yaan 625014, Sichuan, China
| | - Yong-Hong Zhou
- Triticeae Research Institute, Sichuan Agricultural University, Wenjiang 611130, Sichuan, China; Key Laboratory of Crop Genetic Resources and Improvement, Ministry of Education, Sichuan Agricultural University, Yaan 625014, Sichuan, China.
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16
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Crhak Khaitova L, Werlemark G, Kovarikova A, Nybom H, Kovarik A. High penetrance of a pan-canina type rDNA family in intersection Rosa hybrids suggests strong selection of bivalent chromosomes in the section Caninae. Cytogenet Genome Res 2014; 143:104-13. [PMID: 24685720 DOI: 10.1159/000360437] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
All dogroses (Rosa sect. Caninae) are characterized by the peculiar canina meiosis in which genetic material is unevenly distributed between female and male gametes. The pan-canina rDNA family (termed beta) appears to be conserved in all dogroses analyzed so far. Here, we have studied rDNAs in experimental hybrids obtained from open pollination of F1 plants derived from 2 independent intersectional crosses between the pentaploid dogrose species (2n = 5x = 35) Rosa rubiginosa as female parent (producing 4x egg cells due to the unique asymmetrical canina meiosis) and the tetraploid (2n = 4x = 28) garden rose R. hybrida 'André Brichet' as male parent (producing 2x pollen after normal meiosis). We analyzed the structure of rDNA units by molecular methods [CAPS and extensive sequencing of internal transcribed spacers (ITS)] and determined the number of loci on chromosomes by FISH. FISH showed that R. rubiginosa and 'André Brichet' harbored 5 and 4 highly heteromorphic rDNA loci, respectively. In the second generation of hybrid lines, we observed a reduced number of loci (4 and 5 instead of the expected 6). In R. rubiginosa and 'André Brichet', 2-3 major ITS types were found which is consistent with a weak homogenization pressure maintaining high diversity of ITS types in this genus. In contrast to expectation (the null hypothesis of Mendelian inheritance of ITS families), we observed reduced ITS diversity in some individuals of the second generation which might derive from self-fertilization or from a backcross to R. rubiginosa. In these individuals, the pan-canina beta family appeared to be markedly enriched, while the paternal families were lost or diminished in copies. Although the mechanism of biased meiotic transmission of certain rDNA types is currently unknown, we speculate that the bivalent-forming chromosomes carrying the beta rDNA family exhibit extraordinary pairing efficiency and/or are subjected to strong selection in Caninae polyploids.
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Affiliation(s)
- Lucie Crhak Khaitova
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno, Czech Republic
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17
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Multiple ITS copies reveal extensive hybridization within Rheum (Polygonaceae), a genus that has undergone rapid radiation. PLoS One 2014; 9:e89769. [PMID: 24587023 PMCID: PMC3937351 DOI: 10.1371/journal.pone.0089769] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Accepted: 01/25/2014] [Indexed: 11/24/2022] Open
Abstract
Background During adaptive radiation events, characters can arise multiple times due to parallel evolution, but transfer of traits through hybridization provides an alternative explanation for the same character appearing in apparently non-sister lineages. The signature of hybridization can be detected in incongruence between phylogenies derived from different markers, or from the presence of two divergent versions of a nuclear marker such as ITS within one individual. Methodology/Principal Findings In this study, we cloned and sequenced ITS regions for 30 species of the genus Rheum, and compared them with a cpDNA phylogeny. Seven species contained two divergent copies of ITS that resolved in different clades from one another in each case, indicating hybridization events too recent for concerted evolution to have homogenised the ITS sequences. Hybridization was also indicated in at least two further species via incongruence in their position between ITS and cpDNA phylogenies. None of the ITS sequences present in these nine species matched those detected in any other species, which provides tentative evidence against recent introgression as an explanation. Rheum globulosum, previously indicated by cpDNA to represent an independent origin of decumbent habit, is indicated by ITS to be part of clade of decumbent species, which acquired cpDNA of another clade via hybridization. However decumbent and glasshouse morphology are confirmed to have arisen three and two times, respectively. Conclusions These findings suggested that hybridization among QTP species of Rheum has been extensive, and that a role of hybridization in diversification of Rheum requires investigation.
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18
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Ge XH, Ding L, Li ZY. Nucleolar dominance and different genome behaviors in hybrids and allopolyploids. PLANT CELL REPORTS 2013; 32:1661-73. [PMID: 23864197 DOI: 10.1007/s00299-013-1475-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 07/01/2013] [Indexed: 05/05/2023]
Abstract
Many plants are allopolyploids with different nuclear genomes from two or more progenitors, but cytoplasmic genomes typically inherited from the female parent. The importance of this speciation mechanism has stimulated the extensive investigations of genetic consequences of genome mergers in several experimental systems during last 20 years. The dynamic nature of polyploid genomes is recognized, and widespread changes to gene expression are revealed by transcriptomic analysis. These progresses show different stabilities of parental genomes and their unequal contributions to the transcriptome, proteome, and phenotype. We review the results in systems where extensive genetic analyses have been conducted and propose possible mechanisms for biased behavior of parental genomes in allopolyploids, including the role of nucleolar dominance. It is hypothesized that the novel ribosomes with rRNAs from uniparental genome and the ribosomal proteins of biparental origins have some impacts on the biased cellular and genetic behaviors of parental genomes in hybrids and allopolyploids.
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Affiliation(s)
- Xian-Hong Ge
- National Key Lab of Crop Genetic Improvement, College of Plant Science and Technology, National Center of Crop Molecular Breeding, National Center of Oil Crop Improvement (Wuhan), Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
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19
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Waminal NE, Ryu KH, Choi SH, Kim HH. Randomly detected genetically modified (GM) maize (Zea mays L.) near a transport route revealed a fragile 45S rDNA phenotype. PLoS One 2013; 8:e74060. [PMID: 24040165 PMCID: PMC3767626 DOI: 10.1371/journal.pone.0074060] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 07/29/2013] [Indexed: 11/18/2022] Open
Abstract
Monitoring of genetically modified (GM) crops has been emphasized to prevent their potential effects on the environment and human health. Monitoring of the inadvertent dispersal of transgenic maize in several fields and transport routes in Korea was carried out by qualitative multiplex PCR, and molecular analyses were conducted to identify the events of the collected GM maize. Cytogenetic investigations through fluorescence in situ hybridization (FISH) of the GM maize were performed to check for possible changes in the 45S rDNA cluster because this cluster was reported to be sensitive to replication and transcription stress. Three GM maize kernels were collected from a transport route near Incheon port, Korea, and each was found to contain NK603, stacked MON863 x NK603, and stacked NK603 x MON810 inserts, respectively. Cytogenetic analysis of the GM maize containing the stacked NK603 x MON810 insert revealed two normal compact 5S rDNA signals, but the 45S rDNA showed a fragile phenotype, demonstrating a “beads-on-a-string” fragmentation pattern, which seems to be a consequence of genetic modification. Implications of the 45S rDNA cluster fragility in GM maize are also discussed.
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Affiliation(s)
- Nomar Espinosa Waminal
- Plant Biotechnology Institute, Department of Life Science, Sahmyook University, Seoul, Korea
- Department of Plant Science, Plant Genomics and Breeding Institute and Research Institute for Agriculture and Life Sciences, College of Agriculture and Life Sciences, Seoul National University, Seoul, Korea
| | - Ki Hyun Ryu
- Department of Horticulture, Biotechnology and Landscape Architecture, Seoul Women’s University, Seoul, Korea
| | - Sun-Hee Choi
- Department of Horticulture, Biotechnology and Landscape Architecture, Seoul Women’s University, Seoul, Korea
| | - Hyun Hee Kim
- Plant Biotechnology Institute, Department of Life Science, Sahmyook University, Seoul, Korea
- * E-mail:
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20
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Weiss-Schneeweiss H, Emadzade K, Jang TS, Schneeweiss G. Evolutionary consequences, constraints and potential of polyploidy in plants. Cytogenet Genome Res 2013; 140:137-50. [PMID: 23796571 PMCID: PMC3859924 DOI: 10.1159/000351727] [Citation(s) in RCA: 133] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Polyploidy, the possession of more than 2 complete genomes, is a major force in plant evolution known to affect the genetic and genomic constitution and the phenotype of an organism, which will have consequences for its ecology and geography as well as for lineage diversification and speciation. In this review, we discuss phylogenetic patterns in the incidence of polyploidy including possible underlying causes, the role of polyploidy for diversification, the effects of polyploidy on geographical and ecological patterns, and putative underlying mechanisms as well as chromosome evolution and evolution of repetitive DNA following polyploidization. Spurred by technological advances, a lot has been learned about these aspects both in model and increasingly also in nonmodel species. Despite this enormous progress, long-standing questions about polyploidy still cannot be unambiguously answered, due to frequently idiosyncratic outcomes and insufficient integration of different organizational levels (from genes to ecology), but likely this will change in the near future. See also the sister article focusing on animals by Choleva and Janko in this themed issue.
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Affiliation(s)
- H. Weiss-Schneeweiss
- Department of Systematic and Evolutionary Botany University of Vienna, Rennweg 14 AT–1030 Vienna (Austria)
| | - K. Emadzade
- Department of Systematic and Evolutionary Botany University of Vienna, Rennweg 14 AT–1030 Vienna (Austria)
| | - T.-S. Jang
- Department of Systematic and Evolutionary Botany University of Vienna, Rennweg 14 AT–1030 Vienna (Austria)
| | - G.M. Schneeweiss
- Department of Systematic and Evolutionary Botany University of Vienna, Rennweg 14 AT–1030 Vienna (Austria)
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21
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Renny-Byfield S, Kovařík A, Chester M, Nichols RA, Macas J, Novák P, Leitch AR. Independent, rapid and targeted loss of highly repetitive DNA in natural and synthetic allopolyploids of Nicotiana tabacum. PLoS One 2012; 7:e36963. [PMID: 22606317 PMCID: PMC3351487 DOI: 10.1371/journal.pone.0036963] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2012] [Accepted: 04/16/2012] [Indexed: 01/20/2023] Open
Abstract
Allopolyploidy (interspecific hybridisation and polyploidy) has played a significant role in the evolutionary history of angiosperms and can result in genomic, epigenetic and transcriptomic perturbations. We examine the immediate effects of allopolyploidy on repetitive DNA by comparing the genomes of synthetic and natural Nicotiana tabacum with diploid progenitors N. tomentosiformis (paternal progenitor) and N. sylvestris (maternal progenitor). Using next generation sequencing, a recently developed graph-based repeat identification pipeline, Southern blot and fluorescence in situ hybridisation (FISH) we characterise two highly repetitive DNA sequences (NicCL3 and NicCL7/30). Analysis of two independent high-throughput DNA sequencing datasets indicates NicCL3 forms 1.6-1.9% of the genome in N. tomentosiformis, sequences that occur in multiple, discontinuous tandem arrays scattered over several chromosomes. Abundance estimates, based on sequencing depth, indicate NicCL3 is almost absent in N. sylvestris and has been dramatically reduced in copy number in the allopolyploid N. tabacum. Surprisingly elimination of NicCL3 is repeated in some synthetic lines of N. tabacum in their forth generation. The retroelement NicCL7/30, which occurs interspersed with NicCL3, is also under-represented but to a much lesser degree, revealing targeted elimination of the latter. Analysis of paired-end sequencing data indicates the tandem component of NicCL3 has been preferentially removed in natural N. tabacum, increasing the proportion of the dispersed component. This occurs across multiple blocks of discontinuous repeats and based on the distribution of nucleotide similarity among NicCL3 units, was concurrent with rounds of sequence homogenisation.
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Affiliation(s)
- Simon Renny-Byfield
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Ales Kovařík
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno, Czech Republic
| | - Michael Chester
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
- Laboratory of Molecular Systematics and Evolutionary Genetics, Florida Museum of Natural History, University of Florida, Gainesville, Florida, United States of America
| | - Richard A. Nichols
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Jiri Macas
- Biology Centre ASCR, Institute of Plant Molecular Biology, České Budějovice, Czech Republic
| | - Petr Novák
- Biology Centre ASCR, Institute of Plant Molecular Biology, České Budějovice, Czech Republic
| | - Andrew R. Leitch
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
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22
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Huang M, Li H, Zhang L, Gao F, Wang P, Hu Y, Yan S, Zhao L, Zhang Q, Tan J, Liu X, He S, Li L. Plant 45S rDNA clusters are fragile sites and their instability is associated with epigenetic alterations. PLoS One 2012; 7:e35139. [PMID: 22509394 PMCID: PMC3324429 DOI: 10.1371/journal.pone.0035139] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2011] [Accepted: 03/08/2012] [Indexed: 12/14/2022] Open
Abstract
Our previous study demonstrated that 45S ribosomal DNA (45S rDNA) clusters were chromosome fragile sites expressed spontaneously in Lolium. In this study, fragile phenotypes of 45S rDNA were observed under aphidicolin (APH) incubation in several plant species. Further actinomycin D (ActD) treatment showed that transcriptional stress might interfere with chromatin packaging, resulting in 45S rDNA fragile expression. These data identified 45S rDNA sites as replication-dependent as well as transcription-dependent fragile sites in plants. In the presence of ActD, a dramatic switch to an open chromatin conformation and accumulated incomplete 5′ end of the external transcribed spacer (5′ETS) transcripts were observed, accompanied by decreased DNA methylation, decreased levels of histone H3, and increased histone acetylation and levels of H3K4me2, suggesting that these epigenetic alterations are associated with failure of 45S rDNA condensation. Furthermore, the finding that γ-H2AX was accumulated at 45S rDNA sites following ActD treatment suggested that the DNA damage signaling pathway was associated with the appearance of 45S rDNA fragile phenotypes. Our data provide a link between 45S rDNA transcription and chromatin-packaging defects and open the door for further identifying the molecular mechanism involved.
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Affiliation(s)
- Min Huang
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Hui Li
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Lu Zhang
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Fei Gao
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Pu Wang
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Yong Hu
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Shihan Yan
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Lin Zhao
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Qi Zhang
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Junjun Tan
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Xincheng Liu
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Shibin He
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
| | - Lijia Li
- State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China
- * E-mail:
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23
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Okuyama Y, Tanabe AS, Kato M. Entangling ancient allotetraploidization in Asian Mitella: an integrated approach for multilocus combinations. Mol Biol Evol 2011; 29:429-39. [PMID: 21940642 DOI: 10.1093/molbev/msr236] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The reconstruction of an ancient polyploidization history is often challenging, although it is a crucial step in clarifying the mechanisms underlying the contemporary success and diversity of polyploids. Phylogenetic relationships of duplicated gene pairs of polyploids, with respect to their orthologs in related diploids, have been used to address this problem, but they often result in conflicting topologies among different genes. Asimitellaria is an East Asian endemic tetraploid lineage of perennials (genus Mitella; Saxifragaceae) that has diversified in riparian habitats. Phylogenetic analyses of four nuclear-encoded, single-copy (per haploid) genes GBSSI-A, GBSSI-B, GS-II, and PepCK all supported a single allopolyploid origin of Asimitellaria, but they did not lead to a consensus about which diploid lineage gave rise to each of the Asimitellaria subgenomes. To address this issue, we used an integrated approach, whereby the four gene data sets and an additional nuclear ribosomal external transcribed spacer and internal transcribed spacer (including a 5.8S ribosomal DNA) data set were concatenated in all possible combinations, and the most probable data combination was determined together with the phylogenetic inference. This resulted in relatively robust support for the two closely related North American diploid species as the ancestral lineages of the Asimitellaria subgenomes, suggesting ancient intercontinental migration of the diploid or tetraploid lineages and subsequent tetraploid diversification in the Japanese Archipelago. The present approach enabled sorting out the duplicated genes into their original combinations in their preduplication ancestors under a maximum-likelihood framework, and its extension toward genome sequencing data may help in the reconstruction of ancestral, preduplicated, whole-genome structures.
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Affiliation(s)
- Yudai Okuyama
- Tsukuba Botanical Garden, National Museum of Nature and Science, Tsukuba, Ibaraki, Japan.
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24
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Marcussen T, Jakobsen KS, Danihelka J, Ballard HE, Blaxland K, Brysting AK, Oxelman B. Inferring species networks from gene trees in high-polyploid North American and Hawaiian violets (Viola, Violaceae). Syst Biol 2011; 61:107-26. [PMID: 21918178 PMCID: PMC3243738 DOI: 10.1093/sysbio/syr096] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The phylogenies of allopolyploids take the shape of networks and cannot be adequately represented as bifurcating trees. Especially for high polyploids (i.e., organisms with more than six sets of nuclear chromosomes), the signatures of gene homoeolog loss, deep coalescence, and polyploidy may become confounded, with the result that gene trees may be congruent with more than one species network. Herein, we obtained the most parsimonious species network by objective comparison of competing scenarios involving polyploidization and homoeolog loss in a high-polyploid lineage of violets (Viola, Violaceae) mostly or entirely restricted to North America, Central America, or Hawaii. We amplified homoeologs of the low-copy nuclear gene, glucose-6-phosphate isomerase (GPI), by single-molecule polymerase chain reaction (PCR) and the chloroplast trnL-F region by conventional PCR for 51 species and subspecies. Topological incongruence among GPI homoeolog subclades, owing to deep coalescence and two instances of putative loss (or lack of detection) of homoeologs, were reconciled by applying the maximum tree topology for each subclade. The most parsimonious species network and the fossil-based calibration of the homoeolog tree favored monophyly of the high polyploids, which has resulted from allodecaploidization 9-14 Ma, involving sympatric ancestors from the extant Viola sections Chamaemelanium (diploid), Plagiostigma (paleotetraploid), and Viola (paleotetraploid). Although two of the high-polyploid lineages (Boreali-Americanae, Pedatae) remained decaploid, recurrent polyploidization with tetraploids of section Plagiostigma within the last 5 Ma has resulted in two 14-ploid lineages (Mexicanae, Nosphinium) and one 18-ploid lineage (Langsdorffianae). This implies a more complex phylogenetic and biogeographic origin of the Hawaiian violets (Nosphinium) than that previously inferred from rDNA data and illustrates the necessity of considering polyploidy in phylogenetic and biogeographic reconstruction.
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Affiliation(s)
- Thomas Marcussen
- 1Department of Biology, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066 Blindern, NO-0316 Oslo, Norway
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Weiss-Schneeweiss H, Blöch C, Turner B, Villaseñor JL, Stuessy TF, Schneeweiss GM. The promiscuous and the chaste: frequent allopolyploid speciation and its genomic consequences in American daisies (Melampodium sect. Melampodium; Asteraceae). Evolution 2011; 66:211-28. [PMID: 22220876 DOI: 10.1111/j.1558-5646.2011.01424.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Polyploidy, an important factor in eukaryotic evolution, is especially abundant in angiosperms, where it often acts in concert with hybridization to produce allopolyploids. The application of molecular phylogenetic techniques has identified the origins of numerous allopolyploids, but little is known on genomic and chromosomal consequences of allopolyploidization, despite their important role in conferring divergence of allopolyploids from their parental species. Here, using several plastid and nuclear sequence markers, we clarify the origin of tetra- and hexaploids in a group of American daisies, allowing characterization of genome dynamics in polyploids compared to their diploid ancestors. All polyploid species are allopolyploids. Among the four diploid gene pools, the propensity for allopolyploidization is unevenly distributed phylogenetically with a few species apparently more prone to participate, but the underlying causes remain unclear. Polyploid genomes are characterized by differential loss of ribosomal DNA loci (5S and 35S rDNA), known hotspots of chromosomal evolution, but show genome size additivity, suggesting limited changes beyond those affecting rDNA loci or the presence of processes counterbalancing genome reduction. Patterns of rDNA sequence conversion and provenance of the lost loci are highly idiosyncratic and differ even between allopolyploids of identical parentage, indicating that allopolyploids deriving from the same lower-ploid parental species can follow different evolutionary trajectories.
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Affiliation(s)
- Hanna Weiss-Schneeweiss
- Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria.
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Immediate unidirectional epigenetic reprogramming of NORs occurs independently of rDNA rearrangements in synthetic and natural forms of a polyploid species Brassica napus. Chromosoma 2011; 120:557-71. [DOI: 10.1007/s00412-011-0331-z] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2011] [Revised: 06/23/2011] [Accepted: 07/01/2011] [Indexed: 01/13/2023]
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Paun O, Bateman RM, Fay MF, Luna JA, Moat J, Hedrén M, Chase MW. Altered gene expression and ecological divergence in sibling allopolyploids of Dactylorhiza (Orchidaceae). BMC Evol Biol 2011; 11:113. [PMID: 21521507 PMCID: PMC3112086 DOI: 10.1186/1471-2148-11-113] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2010] [Accepted: 04/26/2011] [Indexed: 01/01/2023] Open
Abstract
Background Hybridization and polyploidy are potent forces that have regularly stimulated plant evolution and adaptation. Dactylorhiza majalis s.s., D. traunsteineri s.l. and D. ebudensis are three allopolyploid species of a polyploid complex formed through unidirectional (and, in the first two cases, recurrent) hybridization between the widespread diploids D. fuchsii and D. incarnata. Differing considerably in geographical extent and ecological tolerance, the three allopolyploids together provide a useful system to explore genomic responses to allopolyploidization and reveal their role in adaptation to contrasting environments. Results Analyses of cDNA-AFLPs show a significant increase in the range of gene expression of these allopolyploid lineages, demonstrating higher potential for phenotypic plasticity than is shown by either parent. Moreover, allopolyploid individuals express significantly more gene variants (including novel alleles) than their parents, providing clear evidence of increased biological complexity following allopolyploidization. More genetic mutations seem to have accumulated in the older D. majalis compared with the younger D. traunsteineri since their respective formation. Conclusions Multiple origins of the polyploids contribute to differential patterns of gene expression with a distinct geographic structure. However, several transcripts conserved within each allopolyploid taxon differ between taxa, indicating that habitat preferences shape similar expression patterns in these independently formed tetraploids. Statistical signals separate several transcripts - some of them novel in allopolyploids - that appear correlated with adaptive traits and seem to play a role favouring the persistence of individuals in their native environments. In addition to stabilizing the allopolyploid genome, genetic and epigenetic alterations are key determinants of adaptive success of the new polyploid species after recurrent allopolyploidization events, potentially triggering reproductive isolation between the resulting lineages.
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Affiliation(s)
- Ovidiu Paun
- Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg, Austria.
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Ritz CM, Köhnen I, Groth M, Theißen G, Wissemann V. To be or not to be the odd one out--allele-specific transcription in pentaploid dogroses (Rosa L. sect. Caninae (DC.) Ser). BMC PLANT BIOLOGY 2011; 11:37. [PMID: 21345190 PMCID: PMC3053229 DOI: 10.1186/1471-2229-11-37] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2010] [Accepted: 02/23/2011] [Indexed: 05/18/2023]
Abstract
BACKGROUND Multiple hybridization events gave rise to pentaploid dogroses which can reproduce sexually despite their uneven ploidy level by the unique canina meiosis. Two homologous chromosome sets are involved in bivalent formation and are transmitted by the haploid pollen grains and the tetraploid egg cells. In addition the egg cells contain three sets of univalent chromosomes which are excluded from recombination. In this study we investigated whether differential behavior of chromosomes as bivalents or univalents is reflected by sequence divergence or transcription intensity between homeologous alleles of two single copy genes (LEAFY, cGAPDH) and one ribosomal DNA locus (nrITS). RESULTS We detected a maximum number of four different alleles of all investigated loci in pentaploid dogroses and identified the respective allele with two copies, which is presumably located on bivalent forming chromosomes. For the alleles of the ribosomal DNA locus and cGAPDH only slight, if any, differential transcription was determined, whereas the LEAFY alleles with one copy were found to be significantly stronger expressed than the LEAFY allele with two copies. Moreover, we found for the three marker genes that all alleles have been under similar regimes of purifying selection. CONCLUSIONS Analyses of both molecular sequence evolution and expression patterns did not support the hypothesis that unique alleles probably located on non-recombining chromosomes are less functional than duplicate alleles presumably located on recombining chromosomes.
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Affiliation(s)
- Christiane M Ritz
- Department of Botany, Senckenberg Museum of Natural History Görlitz, Am Museum 1, D-02826 Görlitz, Germany
| | - Ines Köhnen
- Ziegenhainer Straße 19, D-07749 Jena, Germany
| | - Marco Groth
- Genome Analysis, Leibniz Institute for Age Research - Fritz Lipmann Institute, Beutenbergstraße 11, D-07745 Jena, Germany
| | - Günter Theißen
- Department of Genetics, Friedrich Schiller University Jena, Philosophenweg 12, D-07743 Jena, Germany
| | - Volker Wissemann
- Department of Systematic Botany, Institute of Botany, Justus Liebig University Gießen, Heinrich-Buff-Ring 38, D-35392 Gießen, Germany
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Marques A, Fuchs J, Ma L, Heckmann S, Guerra M, Houben A. Characterization of Eu- and heterochromatin of citrus with a focus on the condensation behavior of 45S rDNA chromatin. Cytogenet Genome Res 2011; 134:72-82. [PMID: 21304248 DOI: 10.1159/000323971] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/17/2010] [Indexed: 11/19/2022] Open
Abstract
To characterize the properties of eu- and heterochromatic regions in Citrus species, the chromosomal distribution of different histone H3 marks, DNA methylation sites (5mC) and 45S ribosomal DNA sites were determined for C. clementina, C. paradisi, C. sinensis, and for the hybrid Ortanique C. reticulata × C. sinensis. Our data show that in the relatively small genomes of investigated Citrus species (genome size ranges from 378-400 Mbp) the euchromatin is characterized by histone H3 lysine 4 mono-, di- and trimethylation (H3K4me1/ 2/3) and histone H3 lysine 9 trimethylation (H3K9me3). In contrast, histone H3 lysine 9 mono- and dimethylation (H3K9me1/2), histone H3 lysine 27 mono-, di- and trimethylation (H3K27me1/2/3) as well as 5-methylcytosine (5mC) were enriched at certain heterochromatin fractions. Whereas H3K9me1/2 and H3K27me1 were preferentially enriched at the chromomycin A(3)-bright (CMA(+)) heterochromatin, H3K27me2/3 showed a higher accumulation at the DAPI brightly-stained heterochromatin. 5mC signals were associated with most of the CMA(+) areas as well as with the DAPI strongly-stained heterochromatin fraction. Therefore, extensive methylation of DNA as well as of H3K9me1/2 and H3K27me1/2/3, and depletion of H3K4me1/2/3 and H3K9me3 appear to be specific features of heterochromatin in Citrus. Transcriptionally active decondensed 45S rDNA sites were found DNA hypomethylated, while the silenced condensed sites were strongly 5mC methylated. Although the number of chromosomal 45S rDNA sites differed between the species, the number of transcriptionally active rDNA sites remains constant.
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Affiliation(s)
- A Marques
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Germany
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Malinska H, Tate JA, Matyasek R, Leitch AR, Soltis DE, Soltis PS, Kovarik A. Similar patterns of rDNA evolution in synthetic and recently formed natural populations of Tragopogon (Asteraceae) allotetraploids. BMC Evol Biol 2010; 10:291. [PMID: 20858289 PMCID: PMC2955031 DOI: 10.1186/1471-2148-10-291] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2010] [Accepted: 09/22/2010] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND Tragopogon mirus and T. miscellus are allotetraploids (2n = 24) that formed repeatedly during the past 80 years in eastern Washington and adjacent Idaho (USA) following the introduction of the diploids T. dubius, T. porrifolius, and T. pratensis (2n = 12) from Europe. In most natural populations of T. mirus and T. miscellus, there are far fewer 35S rRNA genes (rDNA) of T. dubius than there are of the other diploid parent (T. porrifolius or T. pratensis). We studied the inheritance of parental rDNA loci in allotetraploids resynthesized from diploid accessions. We investigate the dynamics and directionality of these rDNA losses, as well as the contribution of gene copy number variation in the parental diploids to rDNA variation in the derived tetraploids. RESULTS Using Southern blot hybridization and fluorescent in situ hybridization (FISH), we analyzed copy numbers and distribution of these highly reiterated genes in seven lines of synthetic T. mirus (110 individuals) and four lines of synthetic T. miscellus (71 individuals). Variation among diploid parents accounted for most of the observed gene imbalances detected in F1 hybrids but cannot explain frequent deviations from repeat additivity seen in the allotetraploid lines. Polyploid lineages involving the same diploid parents differed in rDNA genotype, indicating that conditions immediately following genome doubling are crucial for rDNA changes. About 19% of the resynthesized allotetraploid individuals had equal rDNA contributions from the diploid parents, 74% were skewed towards either T. porrifolius or T. pratensis-type units, and only 7% had more rDNA copies of T. dubius-origin compared to the other two parents. Similar genotype frequencies were observed among natural populations. Despite directional reduction of units, the additivity of 35S rDNA locus number is maintained in 82% of the synthetic lines and in all natural allotetraploids. CONCLUSIONS Uniparental reductions of homeologous rRNA gene copies occurred in both synthetic and natural populations of Tragopogon allopolyploids. The extent of these rDNA changes was generally higher in natural populations than in the synthetic lines. We hypothesize that locus-specific and chromosomal changes in early generations of allopolyploids may influence patterns of rDNA evolution in later generations.
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Affiliation(s)
- Hana Malinska
- Institute of Biophysics, Academy of Sciences of the Czech Republic, vvi Laboratory of Molecular Epigenetics, Kralovopolska 135, CZ-61265 Brno, Czech Republic
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Buggs RJA, Chamala S, Wu W, Gao L, May GD, Schnable PS, Soltis DE, Soltis PS, Barbazuk WB. Characterization of duplicate gene evolution in the recent natural allopolyploid Tragopogon miscellus by next-generation sequencing and Sequenom iPLEX MassARRAY genotyping. Mol Ecol 2010; 19 Suppl 1:132-46. [PMID: 20331776 DOI: 10.1111/j.1365-294x.2009.04469.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Tragopogon miscellus (Asteraceae) is an evolutionary model for the study of natural allopolyploidy, but until now has been under-resourced as a genetic model. Using 454 and Illumina expressed sequence tag sequencing of the parental diploid species of T. miscellus, we identified 7782 single nucleotide polymorphisms that differ between the two progenitor genomes present in this allotetraploid. Validation of a sample of 98 of these SNPs in genomic DNA using Sequenom MassARRAY iPlex genotyping confirmed 92 SNP markers at the genomic level that were diagnostic for the two parental genomes. In a transcriptome profile of 2989 SNPs in a single T. miscellus leaf, using Illumina sequencing, 69% of SNPs showed approximately equal expression of both homeologs (duplicate homologous genes derived from different parents), 22% showed apparent differential expression and 8.5% showed apparent silencing of one homeolog in T. miscellus. The majority of cases of homeolog silencing involved the T. dubius SNP homeolog (164/254; 65%) rather than the T. pratensis homeolog (90/254). Sequenom analysis of genomic DNA showed that in a sample of 27 of the homeologs showing apparent silencing, 23 (85%) were because of genomic homeolog loss. These methods could be applied to any organism, allowing efficient and cost-effective generation of genetic markers.
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Affiliation(s)
- Richard J A Buggs
- Department of Biology, University of Florida, Gainesville, 32611, USA
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Buggs RJA, Elliott NM, Zhang L, Koh J, Viccini LF, Soltis DE, Soltis PS. Tissue-specific silencing of homoeologs in natural populations of the recent allopolyploid Tragopogon mirus. THE NEW PHYTOLOGIST 2010; 186:175-83. [PMID: 20409177 DOI: 10.1111/j.1469-8137.2010.03205.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Recent years have seen rapid advances in our knowledge of the transcriptomic consequences of allopolyploidy, primarily through the study of polyploid crops and model systems. However, few studies have distinguished between homoeologs and between tissues, and still fewer have examined young natural allopolyploid populations of independent origin, whose parental species are still present in the same location. Here, we examined the expression of 13 homoeolog pairs in seven tissues of 10 plants of allotetraploid Tragopogon mirus from two natural populations formed by independent polyploidizations between Tragopogon dubius and Tragopogon porrifolius c. 40 generations ago. We compare these with patterns of expression in the diploid parental species from the same locality. Of the 910 assays in T. mirus, 576 (63%) showed expression of both homoeologs, 63 (7%) showed no expression of either homoeolog, 186 (20%) showed nonexpression of one homoeolog across all tissues of a plant, and 72 (8%) showed non-expression of a homoeolog in a particular tissue within a plant. We found two cases of reciprocal tissue-specific expression between homoeologs, potentially indicative of subfunctionalization. Our study shows that tissue-specific silencing, and even apparent subfunctionalization, can arise rapidly in the early generations of natural allopolyploidy.
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Affiliation(s)
- Richard J A Buggs
- Department of Biology, University of Florida, Gainesville, FL 32611, USA.
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Khaitová L, Werlemark G, Nybom H, Kovarík A. Frequent silencing of rDNA loci on the univalent-forming genomes contrasts with their stable expression on the bivalent-forming genomes in polyploid dogroses (Rosa sect. Caninae). Heredity (Edinb) 2010; 104:113-20. [PMID: 19639009 DOI: 10.1038/hdy.2009.94] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The polyploid species in Rosa section Caninae (2n=21, 28 or 35) are characterized by an unusual reproductive system known as odd (or asymmetric) meiosis. Only two chromosome sets form bivalents in meiosis, whereas the remaining chromosomes are transmitted as univalents through the female germline. Evolution of ribosomal rRNA genes (rDNA) does not seem to be significantly affected by interlocus homogenization in dogroses. As a consequence, most species contain several rDNA families falling into two main clades (beta and gamma) thought to be differentially distributed between bivalent and univalent chromosomes, respectively. Here, we have investigated expression of rRNA gene families in five pentaploid species (R. canina, R. rubiginosa, R. dumalis, R. sherardii and R. caesia, 2n=35) and in one tetraploid (R. mollis, 2n=28). Using extensive sequencing of ITS clones and cleaved amplified polymorphism sequence (CAPS) analysis, we found that the beta-family was constitutively expressed in all species. However, there was large variation in the expression patterns of families constituting the gamma-clade. In addition, a single family can be active in one species, whereas silenced in another. The data show that the families on bivalent-forming chromosomes dominate rDNA expression in all dogrose species. We hypothesize that genes on bivalent genomes are stably expressed, whereas those on univalent genomes undergo variable levels of epigenetic silencing. Nonetheless, mosaic expression of univalent genomes could contribute to phenotypic variation between the species.
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Affiliation(s)
- L Khaitová
- Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i. Laboratory of Molecular Epigenetics, Brno, Czech Republic
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Marques I, Feliner GN, Draper Munt D, Martins-Loução MA, Aguilar JF. Unraveling cryptic reticulate relationships and the origin of orphan hybrid disjunct populations in Narcissus. Evolution 2010; 64:2353-68. [PMID: 20199565 DOI: 10.1111/j.1558-5646.2010.00983.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Evolutionary consequences of natural hybridization between species may vary so drastically depending on spatial, genetic, and ecological factors that multiple approaches are required to uncover them. To unravel the evolutionary history of a controversial hybrid (Narcissus x perezlarae), here we use four approaches: DNA sequences from five regions (four organellar, one nuclear), cytological studies (chromosome counts and genome size), crossing experiments, and niche modeling. We conclude that (1) it actually consists of two different hybrid taxa, N.xperezlarae s.s. (N. cavanillesii x N. miniatus) and N.xalentejanus (N. cavanillesii x N. serotinus); (2) both have been formed several times independently, that is, polytopically; (3) N. cavanillesii was the mother progenitor in most hybridization events. We also address the origin of orphan hybrid populations of N.xperezlarae in eastern Spain, hundreds of kilometers away from N. cavanillesii. Although long-distance dispersal of already formed hybrids cannot be completely rejected, extirpation of N. cavanillesii via demographic competition is a more likely explanation. Low-reproductive barriers to fertilization by foreign pollen in N. cavanillesii, molecular footprints of the former presence of this species in the area, active asexual propagation by bulbs in N.xperezlarae, and overlapping ecological niches are consistent with the extirpation scenario.
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Affiliation(s)
- Isabel Marques
- Universidade de Lisboa. Museu Nacional de História Natural, Jardim Botânico, Rua da Escola Politécnica 58. 1280-102 Lisboa, Portugal.
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Koh J, Soltis PS, Soltis DE. Homeolog loss and expression changes in natural populations of the recently and repeatedly formed allotetraploid Tragopogon mirus (Asteraceae). BMC Genomics 2010; 11:97. [PMID: 20141639 PMCID: PMC2829515 DOI: 10.1186/1471-2164-11-97] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2009] [Accepted: 02/08/2010] [Indexed: 12/22/2022] Open
Abstract
Background Although polyploidy has long been recognized as a major force in the evolution of plants, most of what we know about the genetic consequences of polyploidy comes from the study of crops and model systems. Furthermore, although many polyploid species have formed repeatedly, patterns of genome evolution and gene expression are largely unknown for natural polyploid populations of independent origin. We therefore examined patterns of loss and expression in duplicate gene pairs (homeologs) in multiple individuals from seven natural populations of independent origin of Tragopogon mirus (Asteraceae), an allopolyploid that formed repeatedly within the last 80 years from the diploids T. dubius and T. porrifolius. Results Using cDNA-AFLPs, we found differential band patterns that could be attributable to gene silencing, novel expression, and/or maternal/paternal effects between T. mirus and its diploid parents. Subsequent cleaved amplified polymorphic sequence (CAPS) analyses of genomic DNA and cDNA revealed that 20 of the 30 genes identified through cDNA-AFLP analysis showed additivity, whereas nine of the 30 exhibited the loss of one parental homeolog in at least one individual. Homeolog loss (versus loss of a restriction site) was confirmed via sequencing. The remaining gene (ADENINE-DNA GLYCOSYLASE) showed ambiguous patterns in T. mirus because of polymorphism in the diploid parent T. dubius. Most (63.6%) of the homeolog loss events were of the T. dubius parental copy. Two genes, NUCLEAR RIBOSOMAL DNA and GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE, showed differential expression of the parental homeologs, with the T. dubius copy silenced in some individuals of T. mirus. Conclusions Genomic and cDNA CAPS analyses indicated that plants representing multiple populations of this young natural allopolyploid have experienced frequent and preferential elimination of homeologous loci. Comparable analyses of synthetic F1 hybrids showed only additivity. These results suggest that loss of homeologs and changes in gene expression are not the immediate result of hybridization, but are processes that occur following polyploidization, occurring during the early (<40) generations of the young polyploid. Both T. mirus and a second recently formed allopolyploid, T. miscellus, exhibit more homeolog losses than gene silencing events. Furthermore, both allotetraploids undergo biased loss of homeologs contributed by their shared diploid parent, T. dubius. Further studies are required to assess whether the results for the 30 genes so far examined are representative of the entire genome.
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Affiliation(s)
- Jin Koh
- Department of Biology, University of Florida, Gainesville, Florida 32611, USA.
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Bao Y, Wendel JF, Ge S. Multiple patterns of rDNA evolution following polyploidy in Oryza. Mol Phylogenet Evol 2009; 55:136-142. [PMID: 19857580 DOI: 10.1016/j.ympev.2009.10.023] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Revised: 10/06/2009] [Accepted: 10/18/2009] [Indexed: 10/20/2022]
Abstract
Ribosomal ITS sequences are commonly used for phylogenetic reconstruction because they are included in rDNA repeats, and hence are ubiquitous and present in high copy number. Ribosomal rDNA repeats often undergo rapid concerted evolution within and between arrays. Interspecific hybridization merges divergent repeat types in a single nucleus, setting in motion evolutionary processes leading to coexistence, maintenance of paralogs, origin of novel sequence variants, loss of arrays, or inter-array sequence homogenization via concerted evolution. Here we examined ITS polymorphism within and among six Oryza tetraploids of varying genomic composition to infer the extent and direction of concerted evolution following allopolyploid speciation. We demonstrate that different polyploids have experienced varying fates, including maintenance or homogenization of divergent arrays, even among allopolyploids having the same genomic origins but in different geographic locations. Bidirectional concerted evolution, in which arrays become homogenized to alternative progenitor diploid types in different allopolyploid derivatives, is evident among species in one clade. Our results exemplify the panoply of outcomes for ribosomal DNA evolution following allopolyploid speciation.
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Affiliation(s)
- Ying Bao
- College of Life Science, Qufu Normal University, Qufu, Shandong 273165, PR China; State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, PR China.
| | - Jonathan F Wendel
- Department of Ecology, Evolution, & Organismal Biology, Iowa State University, Ames, IA 50011, United States
| | - Song Ge
- State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, PR China
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Allopolyploid origin of Mediterranean species inHelictotrichon(Poaceae) and its consequences for karyotype repatterning and homogenisation of rDNA repeat units. SYST BIODIVERS 2009. [DOI: 10.1017/s1477200009003041] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Tate JA, Joshi P, Soltis KA, Soltis PS, Soltis DE. On the road to diploidization? Homoeolog loss in independently formed populations of the allopolyploid Tragopogon miscellus (Asteraceae). BMC PLANT BIOLOGY 2009; 9:80. [PMID: 19558696 PMCID: PMC2708164 DOI: 10.1186/1471-2229-9-80] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2009] [Accepted: 06/27/2009] [Indexed: 05/18/2023]
Abstract
BACKGROUND Polyploidy (whole-genome duplication) is an important speciation mechanism, particularly in plants. Gene loss, silencing, and the formation of novel gene complexes are some of the consequences that the new polyploid genome may experience. Despite the recurrent nature of polyploidy, little is known about the genomic outcome of independent polyploidization events. Here, we analyze the fate of genes duplicated by polyploidy (homoeologs) in multiple individuals from ten natural populations of Tragopogon miscellus (Asteraceae), all of which formed independently from T. dubius and T. pratensis less than 80 years ago. RESULTS Of the 13 loci analyzed in 84 T. miscellus individuals, 11 showed loss of at least one parental homoeolog in the young allopolyploids. Two loci were retained in duplicate for all polyploid individuals included in this study. Nearly half (48%) of the individuals examined lost a homoeolog of at least one locus, with several individuals showing loss at more than one locus. Patterns of loss were stochastic among individuals from the independently formed populations, except that the T. dubius copy was lost twice as often as T. pratensis. CONCLUSION This study represents the most extensive survey of the fate of genes duplicated by allopolyploidy in individuals from natural populations. Our results indicate that the road to genome downsizing and ultimate genetic diploidization may occur quickly through homoeolog loss, but with some genes consistently maintained as duplicates. Other genes consistently show evidence of homoeolog loss, suggesting repetitive aspects to polyploid genome evolution.
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Affiliation(s)
- Jennifer A Tate
- Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
| | - Prashant Joshi
- Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
| | - Kerry A Soltis
- Department of Biology, University of Florida, Gainesville, Florida, USA
| | - Pamela S Soltis
- Florida Museum of Natural History, University of Florida, Gainesville, Florida, USA
- Genetics Institute, University of Florida, Gainesville, Florida, USA
| | - Douglas E Soltis
- Department of Biology, University of Florida, Gainesville, Florida, USA
- Genetics Institute, University of Florida, Gainesville, Florida, USA
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Tate JA, Symonds VV, Doust AN, Buggs RJA, Mavrodiev E, Majure LC, Soltis PS, Soltis DE. Synthetic polyploids of Tragopogon miscellus and T. mirus (Asteraceae): 60 Years after Ownbey's discovery. AMERICAN JOURNAL OF BOTANY 2009; 96:979-988. [PMID: 21628250 DOI: 10.3732/ajb.0800299] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In plants, polyploidy has been a significant evolutionary force on both recent and ancient time scales. In 1950, Ownbey reported two newly formed Tragopogon allopolyploids in the northwestern United States. We have made the first synthetic lines of T. mirus and T. miscellus using T. dubius, T. porrifolius, and T. pratensis as parents and colchicine treatment of F(1) hybrids. We also produced allotetraploids between T. porrifolius and T. pratensis, which are not known from nature. We report on the crossability between the diploids, as well as the inflorescence morphology, pollen size, meiotic behavior, and fertility of the synthetic polyploids. Morphologically, the synthetics resemble the natural polyploids with short- and long-liguled forms of T. miscellus resulting when T. pratensis and T. dubius are reciprocally crossed. Synthetic T. mirus was also formed reciprocally, but without any obvious morphological differences resulting from the direction of the cross. Of the 27 original crosses that yielded 171 hybrid individuals, 18 of these lineages have persisted to produce 386 S(1) progeny; each of these lineages has produced S(2) seed that are viable. The successful generation of these synthetic polyploids offers the opportunity for detailed comparative studies of natural and synthetic polyploids within a nonmodel system.
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Affiliation(s)
- Jennifer A Tate
- Massey University, Institute of Molecular BioSciences, Palmerston North, New Zealand
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Buggs RJA, Doust AN, Tate JA, Koh J, Soltis K, Feltus FA, Paterson AH, Soltis PS, Soltis DE. Gene loss and silencing in Tragopogon miscellus (Asteraceae): comparison of natural and synthetic allotetraploids. Heredity (Edinb) 2009; 103:73-81. [PMID: 19277058 DOI: 10.1038/hdy.2009.24] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Whole-genome duplication (polyploidisation) is a widespread mechanism of speciation in plants. Over time, polyploid genomes tend towards a more diploid-like state, through downsizing and loss of duplicated genes (homoeologues), but relatively little is known about the timing of gene loss during polyploid formation and stabilisation. Several studies have also shown gene transcription to be affected by polyploidisation. Here, we examine patterns of gene loss in 10 sets of homoeologues in five natural populations of the allotetraploid Tragopogon miscellus that arose within the past 80 years following independent whole-genome duplication events. We also examine 44 first-generation synthetic allopolyploids of the same species. No cases of homoeologue loss arose in the first allopolyploid generation, but after 80 years, 1.6% of homoeologues were lost in natural populations. For seven homoeologue sets we also examined transcription, finding that 3.4% of retained homoeologues had been silenced in the natural populations, but none in the synthetic plants. The homoeologue losses and silencing events found were not fixed within natural populations and did not form a predictable pattern among populations. We therefore show haphazard loss and silencing of homoeologues, occurring within decades of polyploid formation in T. miscellus, but not in the initial generation.
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Affiliation(s)
- R J A Buggs
- Department of Biology, University of Florida, Gainesville, FL 32611, USA.
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Doyle JJ, Flagel LE, Paterson AH, Rapp RA, Soltis DE, Soltis PS, Wendel JF. Evolutionary genetics of genome merger and doubling in plants. Annu Rev Genet 2009; 42:443-61. [PMID: 18983261 DOI: 10.1146/annurev.genet.42.110807.091524] [Citation(s) in RCA: 428] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Polyploidy is a common mode of evolution in flowering plants. The profound effects of polyploidy on gene expression appear to be caused more by hybridity than by genome doubling. Epigenetic mechanisms underlying genome-wide changes in expression are as yet poorly understood; only methylation has received much study, and its importance varies among polyploids. Genetic diploidization begins with the earliest responses to genome merger and doubling; less is known about chromosomal diploidization. Polyploidy duplicates every gene in the genome, providing the raw material for divergence or partitioning of function in homoeologous copies. Preferential retention or loss of genes occurs in a wide range of taxa, suggesting that there is an underlying set of principles governing the fates of duplicated genes. Further studies are required for general patterns to be elucidated, involving different plant families, kinds of polyploidy, and polyploids of different ages.
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Affiliation(s)
- Jeff J Doyle
- Department of Plant Biology, Cornell University, Ithaca, New York 14850, USA.
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Abstract
The importance of hybridization in plant speciation and evolution has been debated for decades, with opposing views of hybridization as either a creative evolutionary force or evolutionary noise. Hybrid speciation may occur at either the homoploid (i.e., between two species of the same ploidy) or the polyploid level, each with its attendant genetic and evolutionary consequences. Whereas allopolyploidy (i.e., resulting from hybridization and genome doubling) has long been recognized as an important mode of plant speciation, the implications of genome duplication have typically not been taken into account in most fields of plant biology. Recent developments in genomics are revolutionizing our views of angiosperm genomes, demonstrating that perhaps all angiosperms have likely undergone at least one round of polyploidization and that hybridization has been an important force in generating angiosperm species diversity. Hybridization and polyploid formation continue to generate species diversity, with several new allopolyploids having originated just within the past century or so. The origins of polyploid species-whether via hybridization between species or between genetically differentiated populations of a single species-and the immediate genetic consequences of polyploid formation are therefore receiving enthusiastic attention. The time is therefore right for a review of the role of hybridization in plant speciation.
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Affiliation(s)
- Pamela S Soltis
- The Genetics Institute, Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611, USA.
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Quantitative analysis of NOR expression in a B chromosome of the grasshopper Eyprepocnemis plorans. Chromosoma 2008; 118:291-301. [PMID: 19048264 DOI: 10.1007/s00412-008-0197-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2008] [Revised: 11/06/2008] [Accepted: 11/12/2008] [Indexed: 10/21/2022]
Abstract
The B24 chromosome in the Torrox population of the grasshopper Eyprepocnemis plorans is recurrently attached to a nucleolus in diplotene cells, indicating the activity of its distally located ribosomal DNA (rDNA). The frequency of males expressing the B chromosome nucleolus organizer region (B-NOR) almost doubled in 4 years. The likelihood of expressing the B-NOR increased with the B number and, in males expressing it, about 20% of their cells showed a nucleolus attached to the B. When active, the B-NOR contributed more than 25% of total cell nucleolar area (NA). Within males expressing the B-NOR, total cell NA did not differ between cells showing the active or inactive B-NOR, suggesting that total cell NA is tightly regulated in this species. However, this parameter tended to increase in this population from 1999 to 2004, in parallel to the neutralization process which is taking place in this population. Finally, an analysis of A chromosome NOR interdependence for activity revealed a positive correlation among autosomes but a negative correlation between autosomes and the X chromosome, the manifestation of which depends on B-NOR activity. These results are discussed in the context of the nucleolus as a sensor of the stress caused by parasitic B chromosomes.
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Hegarty MJ, Barker GL, Brennan AC, Edwards KJ, Abbott RJ, Hiscock SJ. Changes to gene expression associated with hybrid speciation in plants: further insights from transcriptomic studies in Senecio. Philos Trans R Soc Lond B Biol Sci 2008; 363:3055-69. [PMID: 18579474 DOI: 10.1098/rstb.2008.0080] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Interspecific hybridization is an important mechanism of speciation in higher plants. In flowering plants, hybrid speciation is usually associated with polyploidy (allopolyploidy), but hybrid speciation without genome duplication (homoploid hybrid speciation) is also possible, although it is more difficult to detect. The combination of divergent genomes within a hybrid can result in profound changes to both genome and transcriptome. Recent transcriptomic studies of wild and resynthesized homoploid and allopolyploid hybrids have revealed widespread changes to gene expression in hybrids relative to expression levels in their parents. Many of these changes to gene expression are 'non-additive', i.e. not simply the sum of the combined expression levels of parental genes. Some gene expression changes are far outside the range of gene expression in either parent, and can therefore be viewed as 'transgressive'. Such profound changes to gene expression may enable new hybrids to survive in novel habitats not accessible to their parent species. Here, we give a brief overview of hybrid speciation in plants, with an emphasis on genomic change, before focusing discussion on findings from recent transcriptomic studies. We then discuss our current work on gene expression change associated with hybrid speciation in the genus Senecio (ragworts and groundsels) focusing on the findings from a reanalysis of gene expression data obtained from recent microarray studies of wild and resynthesized allopolyploid Senecio cambrensis. These data, showing extensive non-additive and transgressive gene expression changes in Senecio hybrids, are discussed in the light of findings from other model systems, and in the context of the potential importance of gene expression change to hybrid speciation in plants.
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Affiliation(s)
- Matthew J Hegarty
- School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
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Rapid chromosome evolution in recently formed polyploids in Tragopogon (Asteraceae). PLoS One 2008; 3:e3353. [PMID: 18843372 PMCID: PMC2556386 DOI: 10.1371/journal.pone.0003353] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2008] [Accepted: 09/08/2008] [Indexed: 12/27/2022] Open
Abstract
Background Polyploidy, frequently termed “whole genome duplication”, is a major force in the evolution of many eukaryotes. Indeed, most angiosperm species have undergone at least one round of polyploidy in their evolutionary history. Despite enormous progress in our understanding of many aspects of polyploidy, we essentially have no information about the role of chromosome divergence in the establishment of young polyploid populations. Here we investigate synthetic lines and natural populations of two recently and recurrently formed allotetraploids Tragopogon mirus and T. miscellus (formed within the past 80 years) to assess the role of aberrant meiosis in generating chromosomal/genomic diversity. That diversity is likely important in the formation, establishment and survival of polyploid populations and species. Methodology/Principal Findings Applications of fluorescence in situ hybridisation (FISH) to natural populations of T. mirus and T. miscellus suggest that chromosomal rearrangements and other chromosomal changes are common in both allotetraploids. We detected extensive chromosomal polymorphism between individuals and populations, including (i) plants monosomic and trisomic for particular chromosomes (perhaps indicating compensatory trisomy), (ii) intergenomic translocations and (iii) variable sizes and expression patterns of individual ribosomal DNA (rDNA) loci. We even observed karyotypic variation among sibling plants. Significantly, translocations, chromosome loss, and meiotic irregularities, including quadrivalent formation, were observed in synthetic (S0 and S1 generations) polyploid lines. Our results not only provide a mechanism for chromosomal variation in natural populations, but also indicate that chromosomal changes occur rapidly following polyploidisation. Conclusions/Significance These data shed new light on previous analyses of genome and transcriptome structures in de novo and establishing polyploid species. Crucially our results highlight the necessity of studying karyotypes in young (<150 years old) polyploid species and synthetic polyploids that resemble natural species. The data also provide insight into the mechanisms that perturb inheritance patterns of genetic markers in synthetic polyploids and populations of young natural polyploid species.
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Kovarik A, Werlemark G, Leitch AR, Souckova-Skalicka K, Lim YK, Khaitová L, Koukalova B, Nybom H. The asymmetric meiosis in pentaploid dogroses (Rosa sect. Caninae) is associated with a skewed distribution of rRNA gene families in the gametes. Heredity (Edinb) 2008; 101:359-67. [PMID: 18648391 DOI: 10.1038/hdy.2008.63] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
In pentaploid dogroses, Rosa section Caninae (2n=5x=35), the pollen transmits one basic genome (x=7) derived from the seven segregating bivalents, whereas the egg transmits four basic genomes (4x=28) one set derived from the segregation of seven bivalents and three sets of univalent-forming chromosomes. Chromosomes from all five genomes carry 18-5.8-26S nuclear ribosomal DNA (rDNA) sites. This mode of sexual reproduction, known as permanent odd polyploidy, can potentially lead to the independent evolution of rDNA on bivalent- and univalent-forming chromosomes. To test this hypothesis, we analyzed rRNA gene families in pollen and somatic leaf tissue of R. canina, R. rubiginosa and R. dumalis. Six major rRNA gene families (alpha, beta, beta' gamma, delta and epsilon) were identified based on several highly polymorphic sites in the internal transcribed spacers (ITSs). At least two of the major rRNA gene families were found in each species indicating that rDNAs have not been homogenized across subgenomes. A comparison of ITS1 sequences from leaf and pollen showed differences: the shared beta rRNA gene family was more abundant among pollen clones compared to leaf clones and must constitute a major part of the rDNA loci on bivalent-forming chromosomes. The gamma and delta families were underrepresented in pollen genomes and are probably located predominantly (or solely) on the univalents. The results support the hypothesis that pentaploid dogroses inherited a bivalent-forming genome from a common proto-canina ancestor, a likely donor of the beta rDNA family. Allopolyploidy with distantly related species is likely to have driven evolution of Rosa section Caninae.
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Affiliation(s)
- A Kovarik
- Laboratory of Molecular Epigenetics, Academy of Sciences of the Czech Republic, v.v.i., Institute of Biophysics, Brno, Czech Republic.
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Second G, Rouhan G. Human-mediated emergence as a weed and invasive radiation in the wild of the CD genome allotetraploid rice species (Oryza, Poaceae) in the Neotropics. PLoS One 2008; 3:e2613. [PMID: 18596981 PMCID: PMC2434201 DOI: 10.1371/journal.pone.0002613] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Accepted: 06/09/2008] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The genus Oryza is being used as a model in plant genomic studies although there are several issues still to be resolved regarding the spatio-temporal evolution of this ancient genus. Particularly contentious is whether undated transoceanic natural dispersal or recent human interference has been the principal agent determining its present distribution and differentiation. In this context, we studied the origin and distribution history of the allotetraploid CD rice genome. It is endemic to the Neotropics but the genus is thought to have originated in the Paleotropics, and there is relatively little genetic divergence between some orthologous sequences of the C genome component and their Old World counterparts. METHODOLOGY/PRINCIPAL FINDINGS Because of its allotetraploidy, there are several potential pitfalls in trying to date the formation of the CD genome using molecular data and this could lead to erroneous estimates. Therefore, we rather chose to rely on historical evidence to determine whether or not the CD genome was present in the Neotropics before the arrival of Columbus. We searched early collections of herbarium specimens and studied the reports of explorers of the tropical Americas for references to rice. In spite of numerous collectors traveling inland and collecting Oryza, plants determined as CD genome species were not observed away from cultivated rice fields until 1869. Various arguments suggest that they only consisted of weedy forms until that time. CONCLUSIONS/SIGNIFICANCE The spatio-temporal distribution of herbarium collections fits a simple biogeographical scenario for the emergence in cultivated rice fields followed by radiation in the wild of the CD genome in the Neotropics during the last four centuries. This probably occurred from species introduced to the Americas by humans and we found no evidence that the CD genome pre-existed in the Old World. We therefore propose a new evolutionary hypothesis for such a recent origin of the CD genome. Moreover, we exemplify how an historical approach can provide potentially important information and help to disentangle the timing of evolutionary events in the history of the Oryza genomes.
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Lim KY, Matyasek R, Kovarik A, Leitch A. Parental origin and genome evolution in the allopolyploid Iris versicolor. ANNALS OF BOTANY 2007; 100:219-24. [PMID: 17591610 PMCID: PMC2735315 DOI: 10.1093/aob/mcm116] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2007] [Revised: 03/26/2007] [Accepted: 05/01/2007] [Indexed: 05/16/2023]
Abstract
BACKGROUND AIMS One of the classic examples of an allopolyploid is Iris versicolor, 'Blue Flag' (2n = 108), first studied by Edgar Anderson and later popularized by George Ledyard Stebbins in cytogenetics and evolutionary text-books. It is revisited here using modern molecular and cytogenetic tools to investigate its putative allopolyploid origin involving progenitors of I. virginica (2n = 70) and I. setosa (2n = 38). METHODS Genomic in situ hybridization (GISH), fluorescent in situ hybridization (FISH) and Southern hybridization with 5S and 18-26S ribosomal DNA (rDNA) probes were used to identify the parental origin of chromosomes, and to study the unit structure, relative abundance and chromosomal location of rDNA sequences. KEY RESULTS GISH shows that I. versicolor has inherited the sum of the chromosome complement from the two progenitor species. In I. versicolor all the 18-26S rDNA units and loci are inherited from the progenitor of I. virginica, those loci from the I. setosa progenitor are absent. In contrast 5S rDNA loci and units from both progenitors are found, although one of the two 5S loci expected from the I. setosa progenitor is absent. CONCLUSIONS These data confirm Anderson's hypothesis that I. versicolor is an allopolyploid involving progenitors of I. virginica and I. setosa. The number of 18-26S rDNA loci in I. versicolor is similar to that of progenitor I. virginica, suggestive of a first stage in genome diploidization. The locus loss is targeted at the I. setosa-origin subgenome, and this is discussed in relation to other polyploidy systems.
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Affiliation(s)
- K Yoong Lim
- School of Biological and Chemical Sciences, Queen Mary, University of London, London E1 4NS, UK.
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