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de Tomás C, Vicient CM. The Genomic Shock Hypothesis: Genetic and Epigenetic Alterations of Transposable Elements after Interspecific Hybridization in Plants. EPIGENOMES 2023; 8:2. [PMID: 38247729 PMCID: PMC10801548 DOI: 10.3390/epigenomes8010002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 12/21/2023] [Accepted: 12/24/2023] [Indexed: 01/23/2024] Open
Abstract
Transposable elements (TEs) are major components of plant genomes with the ability to change their position in the genome or to create new copies of themselves in other positions in the genome. These can cause gene disruption and large-scale genomic alterations, including inversions, deletions, and duplications. Host organisms have evolved a set of mechanisms to suppress TE activity and counter the threat that they pose to genome integrity. These includes the epigenetic silencing of TEs mediated by a process of RNA-directed DNA methylation (RdDM). In most cases, the silencing machinery is very efficient for the vast majority of TEs. However, there are specific circumstances in which TEs can evade such silencing mechanisms, for example, a variety of biotic and abiotic stresses or in vitro culture. Hybridization is also proposed as an inductor of TE proliferation. In fact, the discoverer of the transposons, Barbara McClintock, first hypothesized that interspecific hybridization provides a "genomic shock" that inhibits the TE control mechanisms leading to the mobilization of TEs. However, the studies carried out on this topic have yielded diverse results, showing in some cases a total absence of mobilization or being limited to only some TE families. Here, we review the current knowledge about the impact of interspecific hybridization on TEs in plants and the possible implications of changes in the epigenetic mechanisms.
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Affiliation(s)
| | - Carlos M. Vicient
- Centre for Research in Agricultural Genomics, CRAG (CSIC-IRTA-UAB-UB), Campus UAB, Cerdanyola del Vallès, 08193 Barcelona, Spain
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Tusso S, Suo F, Liang Y, Du LL, Wolf JBW. Reactivation of transposable elements following hybridization in fission yeast. Genome Res 2021; 32:324-336. [PMID: 34907076 PMCID: PMC8805722 DOI: 10.1101/gr.276056.121] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 12/09/2021] [Indexed: 11/29/2022]
Abstract
Hybridization is thought to reactivate transposable elements (TEs) that were efficiently suppressed in the genomes of the parental hosts. Here, we provide evidence for this “genomic shock hypothesis” in the fission yeast Schizosaccharomyces pombe. In this species, two divergent lineages (Sp and Sk) have experienced recent, likely human-induced, hybridization. We used long-read sequencing data to assemble genomes of 37 samples derived from 31 S. pombe strains spanning a wide range of ancestral admixture proportions. A comprehensive TE inventory revealed exclusive presence of long terminal repeat (LTR) retrotransposons. Sequence analysis of active full-length elements, as well as solo LTRs, revealed a complex history of homologous recombination. Population genetic analyses of syntenic sequences placed insertion of many solo LTRs before the split of the Sp and Sk lineages. Most full-length elements were inserted more recently, after hybridization. With the exception of a single full-length element with signs of positive selection, both solo LTRs and, in particular, full-length elements carry signatures of purifying selection indicating effective removal by the host. Consistent with reactivation upon hybridization, the number of full-length LTR retrotransposons, varying extensively from zero to 87 among strains, significantly increases with the degree of genomic admixture. This study gives a detailed account of global TE diversity in S. pombe, documents complex recombination histories within TE elements, and provides evidence for the “genomic shock hypothesis.”
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Affiliation(s)
| | - Fang Suo
- National Institute of Biological Sciences
| | - Yue Liang
- National Institute of Biological Sciences
| | - Li-Lin Du
- National Institute of Biological Sciences
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Smukowski Heil C, Patterson K, Hickey ASM, Alcantara E, Dunham MJ. Transposable Element Mobilization in Interspecific Yeast Hybrids. Genome Biol Evol 2021; 13:6141023. [PMID: 33595639 PMCID: PMC7952228 DOI: 10.1093/gbe/evab033] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/11/2021] [Indexed: 12/13/2022] Open
Abstract
Barbara McClintock first hypothesized that interspecific hybridization could provide a “genomic shock” that leads to the mobilization of transposable elements (TEs). This hypothesis is based on the idea that regulation of TE movement is potentially disrupted in hybrids. However, the handful of studies testing this hypothesis have yielded mixed results. Here, we set out to identify if hybridization can increase transposition rate and facilitate colonization of TEs in Saccharomyces cerevisiae × Saccharomyces uvarum interspecific yeast hybrids. Saccharomyces cerevisiae have a small number of active long terminal repeat retrotransposons (Ty elements), whereas their distant relative S. uvarum have lost the Ty elements active in S. cerevisiae. Although the regulation system of Ty elements is known in S. cerevisiae, it is unclear how Ty elements are regulated in other Saccharomyces species, and what mechanisms contributed to the loss of most classes of Ty elements in S. uvarum. Therefore, we first assessed whether TEs could insert in the S. uvarum sub-genome of a S. cerevisiae × S. uvarum hybrid. We induced transposition to occur in these hybrids and developed a sequencing technique to show that Ty elements insert readily and nonrandomly in the S. uvarum genome. We then used an in vivo reporter construct to directly measure transposition rate in hybrids, demonstrating that hybridization itself does not alter rate of mobilization. However, we surprisingly show that species-specific mitochondrial inheritance can change transposition rate by an order of magnitude. Overall, our results provide evidence that hybridization can potentially facilitate the introduction of TEs across species boundaries and alter transposition via mitochondrial transmission, but that this does not lead to unrestrained proliferation of TEs suggested by the genomic shock theory.
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Affiliation(s)
- Caiti Smukowski Heil
- Department of Genome Sciences, University of Washington, Seattle, Washington, USA
| | - Kira Patterson
- Department of Genome Sciences, University of Washington, Seattle, Washington, USA
| | | | - Erica Alcantara
- Department of Genome Sciences, University of Washington, Seattle, Washington, USA
| | - Maitreya J Dunham
- Department of Genome Sciences, University of Washington, Seattle, Washington, USA
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Heyduk K, McAssey EV, Grimwood J, Shu S, Schmutz J, McKain MR, Leebens-Mack J. Hybridization History and Repetitive Element Content in the Genome of a Homoploid Hybrid, Yucca gloriosa (Asparagaceae). FRONTIERS IN PLANT SCIENCE 2021; 11:573767. [PMID: 33519836 PMCID: PMC7843428 DOI: 10.3389/fpls.2020.573767] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Accepted: 12/17/2020] [Indexed: 05/23/2023]
Abstract
Hybridization in plants results in phenotypic and genotypic perturbations that can have dramatic effects on hybrid physiology, ecology, and overall fitness. Hybridization can also perturb epigenetic control of transposable elements, resulting in their proliferation. Understanding the mechanisms that maintain genomic integrity after hybridization is often confounded by changes in ploidy that occur in hybrid plant species. Homoploid hybrid species, which have no change in chromosome number relative to their parents, offer an opportunity to study the genomic consequences of hybridization in the absence of change in ploidy. Yucca gloriosa (Asparagaceae) is a young homoploid hybrid species, resulting from a cross between Yucca aloifolia and Yucca filamentosa. Previous analyses of ∼11 kb of the chloroplast genome and nuclear-encoded microsatellites implicated a single Y. aloifolia genotype as the maternal parent of Y. gloriosa. Using whole genome resequencing, we assembled chloroplast genomes from 41 accessions of all three species to re-assess the hybrid origins of Y. gloriosa. We further used re-sequencing data to annotate transposon abundance in the three species and mRNA-seq to analyze transcription of transposons. The chloroplast phylogeny and haplotype analysis suggest multiple hybridization events contributing to the origin of Y. gloriosa, with both parental species acting as the maternal donor. Transposon abundance at the superfamily level was significantly different between the three species; the hybrid was frequently intermediate to the parental species in TE superfamily abundance or appeared more similar to one or the other parent. In only one case-Copia LTR transposons-did Y. gloriosa have a significantly higher abundance relative to either parent. Expression patterns across the three species showed little increased transcriptional activity of transposons, suggesting that either no transposon release occurred in Y. gloriosa upon hybridization, or that any transposons that were activated via hybridization were rapidly silenced. The identification and quantification of transposon families paired with expression evidence paves the way for additional work seeking to link epigenetics with the important trait variation seen in this homoploid hybrid system.
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Affiliation(s)
- Karolina Heyduk
- School of Life Sciences, University of Hawai’i at Mānoa, Honolulu, HI, United States
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, United States
| | - Edward V. McAssey
- School of Life Sciences, University of Hawai’i at Mānoa, Honolulu, HI, United States
- Department of Biological Sciences, Quinnipiac University, Hamden, CT, United States
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT, United States
| | - Jane Grimwood
- HudsonAlpha Institute for Biotechnology, Huntsville, AL, United States
| | - Shengqiang Shu
- Lawrence Berkeley National Laboratory, US Department of Energy Joint Genome Institute, Berkeley, CA, United States
| | - Jeremy Schmutz
- HudsonAlpha Institute for Biotechnology, Huntsville, AL, United States
- Lawrence Berkeley National Laboratory, US Department of Energy Joint Genome Institute, Berkeley, CA, United States
| | - Michael R. McKain
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, United States
| | - Jim Leebens-Mack
- Department of Plant Biology, University of Georgia, Athens, GA, United States
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Fingerprinting the genetic variation and intergeneric hybrid dynamics in the family Asteraceae (genera Helianthus, Echinaceae, Tagetes and Verbesina) using iPBS markers. Biologia (Bratisl) 2019. [DOI: 10.2478/s11756-019-00363-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Ma B, Xin Y, Kuang L, He N. Distribution and Characteristics of Transposable Elements in the Mulberry Genome. THE PLANT GENOME 2019; 12:180094. [PMID: 31290922 DOI: 10.3835/plantgenome2018.12.0094] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Mulberry ( C. K. Schneid) leaves have been used as the food for the domesticated silkworm, , for more than 5000 yr, and the mulberry-silkworm relationship is one of the best-known and oldest models of plant defense-insect adaptation. The availability of a genome assembly of mulberry provides us with an opportunity to mine the characteristics and distribution of transposable elements (TEs) in this species and to examine their relationship to genes and gene expression. In this study, a significantly correlated inverse relationship between the percentage coverage of genes and TEs was observed. The TE-rich regions appeared to have a lower percentage of putatively expressed genes. Distribution patterns between different TE superfamilies were detected in the mulberry genome. The elements (the TE making up the greatest proportion of the mulberry genome) were significantly overrepresented within genes in the mulberry genome, and they may have a dominant influence on evolution of the mulberry genome. Approximately 96.93% (330/344) of the TE-containing genes assigned to pathways were assigned to metabolism-related pathways. The TE-related alternative splicing events accounted for 7.58% (402/5,302) of all alternative splicing types in the mulberry genome, suggesting that TEs are one of the driving forces in the formation of the alternatively spliced genes. The results will be valuable in improving our understanding of the important roles of TEs in mulberry genome evolution.
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Ma B, Kuang L, Xin Y, He N. New Insights into Long Terminal Repeat Retrotransposons in Mulberry Species. Genes (Basel) 2019; 10:genes10040285. [PMID: 30970574 PMCID: PMC6523491 DOI: 10.3390/genes10040285] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 03/27/2019] [Accepted: 04/04/2019] [Indexed: 11/16/2022] Open
Abstract
The evolutionary dynamics of long terminal repeat (LTR) retrotransposons in tree genomes has remained largely unknown. The availability of the complete genome sequences of the mulberry tree (Morus notabilis) has offered an unprecedented opportunity for us to characterize these retrotransposon elements. We investigated 202 and 114 families of Copia and Gypsy superfamilies, respectively, comprising 2916 intact elements in the mulberry genome. The tRNAMet was the most frequently used type of tRNA in both superfamilies. Phylogenetic analysis suggested that Copia and Gypsy from mulberry can be grouped into eight and six lineages, respectively. All previously characterized families of such elements could also be found in the mulberry genome. About 95% of the identified Copia and Gypsy full elements were estimated to have been inserted into the mulberry genome within the past 2–3 million years. Meanwhile, the estimated insertion times of members of the three most abundant families of the Copia superfamily (908 members from the three most abundant families) and Gypsy superfamily (783 members from the three most abundant families) revealed divergent life histories. Compared with the situation in Gypsy elements, three families of Copia elements are under positive selection pressure, which suggested that Copia elements may have a dominant influence in the evolution of mulberry genes. Analysis of insertion and deletion dynamics suggested that Copia and Gypsy elements exhibited a very long half-life in the mulberry genome. The present work provides new insights into the insertion and deletion dynamics of LTR retrotransposons, and it will greatly improve our understanding of the important roles transposable elements play in the architecture of the mulberry genome.
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Affiliation(s)
- Bi Ma
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China.
| | - Lulu Kuang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China.
| | - Youchao Xin
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China.
| | - Ningjia He
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China.
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Dennenmoser S, Sedlazeck FJ, Schatz MC, Altmüller J, Zytnicki M, Nolte AW. Genome‐wide patterns of transposon proliferation in an evolutionary young hybrid fish. Mol Ecol 2019; 28:1491-1505. [DOI: 10.1111/mec.14969] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Revised: 10/15/2018] [Accepted: 10/23/2018] [Indexed: 01/19/2023]
Affiliation(s)
- Stefan Dennenmoser
- Institute for Biology and Environmental Sciences Carl von Ossietzky University Oldenburg Oldenburg Germany
| | | | - Michael C. Schatz
- Cold Spring Harbor Laboratory Cold Spring Harbor New York
- Departments of Computer Science and Biology Johns Hopkins University Baltimore Maryland
| | - Janine Altmüller
- Cologne Center for Genomics, and Institute of Human Genetics University of Cologne Cologne Germany
| | | | - Arne W. Nolte
- Institute for Biology and Environmental Sciences Carl von Ossietzky University Oldenburg Oldenburg Germany
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Ma B, Kuang L, Xin Y, Hou F, He N. Reverse transcriptase sequences from mulberry LTR retrotransposons: characterization analysis. Open Life Sci 2017. [DOI: 10.1515/biol-2017-0031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
AbstractCopia and Gypsy play important roles in structural, functional and evolutionary dynamics of plant genomes. In this study, a total of 106 and 101, Copia and Gypsy reverse transcriptase (rt) were amplified respectively in the Morus notabilis genome using degenerate primers. All sequences exhibited high levels of heterogeneity, were rich in AT and possessed higher sequence divergence of Copia rt in comparison to Gypsy rt. Two reasons are likely to account for this phenomenon: a) these elements often experience deletions or fragmentation by illegitimate or unequal homologous recombination in the transposition process; b) strong purifying selective pressure drives the evolution of these elements through “selective silencing” with random mutation and eventual deletion from the host genome. Interestingly, mulberry rt clustered with other rt from distantly related taxa according to the phylogenetic analysis. This phenomenon did not result from horizontal transposable element transfer. Results obtained from fluorescence in situ hybridization revealed that most of the hybridization signals were preferentially concentrated in pericentromeric and distal regions of chromosomes, and these elements may play important roles in the regions in which they are found. Results of this study support the continued pursuit of further functional studies of Copia and Gypsy in the mulberry genome.
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Affiliation(s)
- Bi Ma
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China
| | - Lulu Kuang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China
| | - Youchao Xin
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China
| | - Fei Hou
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China
| | - Ningjia He
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing 400715, China
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Dennenmoser S, Sedlazeck FJ, Iwaszkiewicz E, Li X, Altmüller J, Nolte AW. Copy number increases of transposable elements and protein-coding genes in an invasive fish of hybrid origin. Mol Ecol 2017; 26:4712-4724. [PMID: 28390096 PMCID: PMC5638112 DOI: 10.1111/mec.14134] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Revised: 03/23/2017] [Accepted: 03/27/2017] [Indexed: 12/25/2022]
Abstract
Evolutionary dynamics of structural genetic variation in lineages of hybrid origin is not well explored, although structural mutations may increase in controlled hybrid crosses. We therefore tested whether structural variants accumulate in a fish of recent hybrid origin, invasive Cottus, relative to both parental species Cottus rhenanus and Cottus perifretum. Copy-number variation in exons of 10,979 genes was assessed using comparative genome hybridization arrays. Twelve genes showed significantly higher copy numbers in invasive Cottus compared to both parents. This coincided with increased expression for three genes related to vision, detoxification and muscle development, suggesting possible gene dosage effects. Copy number increases of putative transposons were assessed by comparative mapping of genomic DNA reads against a de novo assembly of 1,005 repetitive elements. In contrast to exons, copy number increases of repetitive elements were common (20.7%) in invasive Cottus, whereas decrease was very rare (0.01%). Among the increased repetitive elements, 53.8% occurred at higher numbers in C. perifretum compared to C. rhenanus, while only 1.4% were more abundant in C. rhenanus. This implies a biased mutational process that amplifies genetic material from one ancestor. To assess the frequency of de novo mutations through hybridization, we screened 64 laboratory-bred F2 offspring between the parental species for copy-number changes at five candidate loci. We found no evidence for new structural variants, indicating that they are too rare to be detected given our sampling scheme. Instead, they must have accumulated over more generations than we observed in a controlled cross.
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Affiliation(s)
- Stefan Dennenmoser
- Department for Evolutionary GeneticsMax‐Planck Institute for Evolutionary BiologyPlönGermany
- Institute for BiologyCarl von Ossietzky University OldenburgOldenburgGermany
| | | | - Elzbieta Iwaszkiewicz
- Department for Evolutionary GeneticsMax‐Planck Institute for Evolutionary BiologyPlönGermany
| | - Xiang‐Yi Li
- Department of Evolutionary Biology and Environmental StudiesUniversity of ZurichZurichSwitzerland
| | - Janine Altmüller
- Cologne Center for Genomics, and Institute of Human GeneticsUniversity of CologneCologneGermany
| | - Arne W. Nolte
- Department for Evolutionary GeneticsMax‐Planck Institute for Evolutionary BiologyPlönGermany
- Institute for BiologyCarl von Ossietzky University OldenburgOldenburgGermany
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Vicient CM, Casacuberta JM. Impact of transposable elements on polyploid plant genomes. ANNALS OF BOTANY 2017; 120:195-207. [PMID: 28854566 PMCID: PMC5737689 DOI: 10.1093/aob/mcx078] [Citation(s) in RCA: 143] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 05/23/2017] [Indexed: 05/18/2023]
Abstract
BACKGROUND The growing wealth of knowledge on whole-plant genome sequences is highlighting the key role of transposable elements (TEs) in plant evolution, as a driver of drastic changes in genome size and as a source of an important number of new coding and regulatory sequences. Together with polyploidization events, TEs should thus be considered the major players in evolution of plants. SCOPE This review outlines the major mechanisms by which TEs impact plant genome evolution and how polyploidy events can affect these impacts, and vice versa. These include direct effects on genes, by providing them with new coding or regulatory sequences, an effect on the epigenetic status of the chromatin close to genes, and more subtle effects by imposing diverse evolutionary constraints to different chromosomal regions. These effects are particularly relevant after polyploidization events. Polyploidization often induces bursts of transposition probably due to a relaxation in their epigenetic control, and, in the short term, this can increase the rate of gene mutations and changes in gene regulation due to the insertion of TEs next to or into genes. Over longer times, TE bursts may induce global changes in genome structure due to inter-element recombination including losses of large genome regions and chromosomal rearrangements that reduce the genome size and the chromosome number as part of a process called diploidization. CONCLUSIONS TEs play an essential role in genome and gene evolution, in particular after polyploidization events. Polyploidization can induce TE activity that may explain part of the new phenotypes observed. TEs may also play a role in the diploidization that follows polyploidization events. However, the extent to which TEs contribute to diploidization and fractionation bias remains unclear. Investigating the multiple factors controlling TE dynamics and the nature of ancient and recent polyploid genomes may shed light on these processes.
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Affiliation(s)
- Carlos M. Vicient
- Center for Research in Agricultural Genomics, CRAG (CSIC-IRTA-UAB-UB), Campus UAB, Cerdanyola del Vallès, 08193 Barcelona, Spain
- For correspondence. E-mail
| | - Josep M. Casacuberta
- Center for Research in Agricultural Genomics, CRAG (CSIC-IRTA-UAB-UB), Campus UAB, Cerdanyola del Vallès, 08193 Barcelona, Spain
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Abstract
LTR retrotransposons are the most abundant group of transposable elements (TEs) in plants. These elements can fall inside or close to genes, and therefore influence their expression and evolution. This review aims to examine how LTR retrotransposons, especially Ty1-copia elements, mediate gene regulation and evolution. Various stimuli, including polyploidization and biotic and abiotic elicitors, result in the transcription and movement of these retrotransposons, and can facilitate adaptation. The presence of cis-regulatory motifs in the LTRs are central to their stress-mediated responses and are shared with host stress-responsive genes, showing a complex evolutionary history in which TEs provide new regulatory units to genes. The presence of retrotransposon remnants in genes that are necessary for normal gene function, demonstrates the importance of exaptation and co-option, and is also a consequence of the abundance of these elements in plant genomes. Furthermore, insertions of LTR retrotransposons in and around genes provide potential for alternative splicing, epigenetic control, transduction, duplication and recombination. These characteristics can become an active part of the evolution of gene families as in the case of resistance genes (R-genes). The character of TEs as exclusively selfish is now being re-evaluated. Since genome-wide reprogramming via TEs is a long evolutionary process, the changes we can examine are case-specific and their fitness advantage may not be evident until TE-derived motifs and domains have been completely co-opted and fixed. Nevertheless, the presence of LTR retrotransposons inside genes and as part of gene promoter regions is consistent with their roles as engines of plant genome evolution.
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Long Terminal Repeat Retrotransposon Content in Eight Diploid Sunflower Species Inferred from Next-Generation Sequence Data. G3-GENES GENOMES GENETICS 2016; 6:2299-308. [PMID: 27233667 PMCID: PMC4978885 DOI: 10.1534/g3.116.029082] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The most abundant transposable elements (TEs) in plant genomes are Class I long terminal repeat (LTR) retrotransposons represented by superfamilies gypsy and copia. Amplification of these superfamilies directly impacts genome structure and contributes to differential patterns of genome size evolution among plant lineages. Utilizing short-read Illumina data and sequence information from a panel of Helianthus annuus (sunflower) full-length gypsy and copia elements, we explore the contribution of these sequences to genome size variation among eight diploid Helianthus species and an outgroup taxon, Phoebanthus tenuifolius. We also explore transcriptional dynamics of these elements in both leaf and bud tissue via RT-PCR. We demonstrate that most LTR retrotransposon sublineages (i.e., families) display patterns of similar genomic abundance across species. A small number of LTR retrotransposon sublineages exhibit lineage-specific amplification, particularly in the genomes of species with larger estimated nuclear DNA content. RT-PCR assays reveal that some LTR retrotransposon sublineages are transcriptionally active across all species and tissue types, whereas others display species-specific and tissue-specific expression. The species with the largest estimated genome size, H. agrestis, has experienced amplification of LTR retrotransposon sublineages, some of which have proliferated independently in other lineages in the Helianthus phylogeny.
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Staton SE, Burke JM. Evolutionary transitions in the Asteraceae coincide with marked shifts in transposable element abundance. BMC Genomics 2015; 16:623. [PMID: 26290182 PMCID: PMC4546089 DOI: 10.1186/s12864-015-1830-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 08/07/2015] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The transposable element (TE) content of the genomes of plant species varies from near zero in the genome of Utricularia gibba to more than 80% in many species. It is not well understood whether this variation in genome composition results from common mechanisms or stochastic variation. The major obstacles to investigating mechanisms of TE evolution have been a lack of comparative genomic data sets and efficient computational methods for measuring differences in TE composition between species. In this study, we describe patterns of TE evolution in 14 species in the flowering plant family Asteraceae and 1 outgroup species in the Calyceraceae to investigate phylogenetic patterns of TE dynamics in this important group of plants. RESULTS Our findings indicate that TE families in the Asteraceae exhibit distinct patterns of non-neutral evolution, and that there has been a directional increase in copy number of Gypsy retrotransposons since the origin of the Asteraceae. Specifically, there is marked increase in Gypsy abundance at the origin of the Asteraceae and at the base of the tribe Heliantheae. This latter shift in genome composition has had a significant impact on the diversity and abundance distribution of TEs in a lineage-specific manner. CONCLUSIONS We show that the TE-driven expansion of plant genomes can be facilitated by just a few TE families, and is likely accompanied by the modification and/or replacement of the TE community. Importantly, large shifts in TE composition may be correlated with major of phylogenetic transitions.
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Affiliation(s)
- S Evan Staton
- Department of Genetics, University of Georgia, Athens, GA, 30602, USA.
- Current address: Beaty Biodiversity Research Centre and Department of Botany, 3529-6270 University Blvd, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
| | - John M Burke
- Department of Plant Biology, University of Georgia, Athens, GA, 30602, USA.
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Renaut S, Rowe HC, Ungerer MC, Rieseberg LH. Genomics of homoploid hybrid speciation: diversity and transcriptional activity of long terminal repeat retrotransposons in hybrid sunflowers. Philos Trans R Soc Lond B Biol Sci 2015; 369:rstb.2013.0345. [PMID: 24958919 DOI: 10.1098/rstb.2013.0345] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Hybridization is thought to play an important role in plant evolution by introducing novel genetic combinations and promoting genome restructuring. However, surprisingly little is known about the impact of hybridization on transposable element (TE) proliferation and the genomic response to TE activity. In this paper, we first review the mechanisms by which homoploid hybrid species may arise in nature. We then present hybrid sunflowers as a case study to examine transcriptional activity of long terminal repeat retrotransposons in the annual sunflowers Helianthus annuus, Helianthus petiolaris and their homoploid hybrid derivatives (H. paradoxus, H. anomalus and H. deserticola) using high-throughput transcriptome sequencing technologies (RNAseq). Sampling homoploid hybrid sunflower taxa revealed abundant variation in TE transcript accumulation. In addition, genetic diversity for several candidate genes hypothesized to regulate TE activity was characterized. Specifically, we highlight one candidate chromatin remodelling factor gene with a direct role in repressing TE activity in a hybrid species. This paper shows that TE amplification in hybrid lineages is more idiosyncratic than previously believed and provides a first step towards identifying the mechanisms responsible for regulating and repressing TE expansions.
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Affiliation(s)
- Sebastien Renaut
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Heather C Rowe
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Mark C Ungerer
- Division of Biology, Kansas State University, 426 Ackert Hall, Manhattan, KS 66506, USA
| | - Loren H Rieseberg
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 Department of Biology, Indiana University, 1001 East Third St., Bloomington, IN 47405, USA
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Crawford DJ, Doyle JJ, Soltis DE, Soltis PS, Wendel JF. Contemporary and future studies in plant speciation, morphological/floral evolution and polyploidy: honouring the scientific contributions of Leslie D. Gottlieb to plant evolutionary biology. Philos Trans R Soc Lond B Biol Sci 2014; 369:20130341. [PMID: 24958916 PMCID: PMC4071516 DOI: 10.1098/rstb.2013.0341] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Affiliation(s)
- Daniel J Crawford
- Department of Ecology and Evolutionary Biology, and Biodiversity Institute, University of Kansas, Lawrence, KS 66045, USA
| | - Jeffrey J Doyle
- L. H. Bailey Hortorium, Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA
| | - Douglas E Soltis
- Department of Biology, University of Florida, Gainesville, FL 17 32611, USA
| | - Pamela S Soltis
- Florida Museum of Natural History, University of Florida, Gainesville, FL 17 32611, USA
| | - Jonathan F Wendel
- Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA
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Gill N, Buti M, Kane N, Bellec A, Helmstetter N, Berges H, Rieseberg LH. Sequence-Based Analysis of Structural Organization and Composition of the Cultivated Sunflower (Helianthus annuus L.) Genome. BIOLOGY 2014; 3:295-319. [PMID: 24833511 PMCID: PMC4085609 DOI: 10.3390/biology3020295] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 03/16/2014] [Accepted: 03/25/2014] [Indexed: 12/19/2022]
Abstract
Sunflower is an important oilseed crop, as well as a model system for evolutionary studies, but its 3.6 gigabase genome has proven difficult to assemble, in part because of the high repeat content of its genome. Here we report on the sequencing, assembly, and analyses of 96 randomly chosen BACs from sunflower to provide additional information on the repeat content of the sunflower genome, assess how repetitive elements in the sunflower genome are organized relative to genes, and compare the genomic distribution of these repeats to that found in other food crops and model species. We also examine the expression of transposable element-related transcripts in EST databases for sunflower to determine the representation of repeats in the transcriptome and to measure their transcriptional activity. Our data confirm previous reports in suggesting that the sunflower genome is >78% repetitive. Sunflower repeats share very little similarity to other plant repeats such as those of Arabidopsis, rice, maize and wheat; overall 28% of repeats are “novel” to sunflower. The repetitive sequences appear to be randomly distributed within the sequenced BACs. Assuming the 96 BACs are representative of the genome as a whole, then approximately 5.2% of the sunflower genome comprises non TE-related genic sequence, with an average gene density of 18kbp/gene. Expression levels of these transposable elements indicate tissue specificity and differential expression in vegetative and reproductive tissues, suggesting that expressed TEs might contribute to sunflower development. The assembled BACs will also be useful for assessing the quality of several different draft assemblies of the sunflower genome and for annotating the reference sequence.
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Affiliation(s)
- Navdeep Gill
- Department of Botany and The Biodiversity Research Centre, University of British Columbia, Vancouver V6T 1Z4, BC, Canada.
| | - Matteo Buti
- Applied Rosaceous Genomics Group, Centre for Research and Innovation, Michele all'Adige (TN) P.IVA 020384102, Italy.
| | - Nolan Kane
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA.
| | - Arnaud Bellec
- French Plant Genomic Resource Centre, INRA-CNRGV, Chemin de Borde Rouge, CS 52627, 31326 Castanet Tolosan, France.
| | - Nicolas Helmstetter
- French Plant Genomic Resource Centre, INRA-CNRGV, Chemin de Borde Rouge, CS 52627, 31326 Castanet Tolosan, France.
| | - Hélène Berges
- French Plant Genomic Resource Centre, INRA-CNRGV, Chemin de Borde Rouge, CS 52627, 31326 Castanet Tolosan, France.
| | - Loren H Rieseberg
- Department of Botany and The Biodiversity Research Centre, University of British Columbia, Vancouver V6T 1Z4, BC, Canada.
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Kantar MB, Baute GJ, Bock DG, Rieseberg LH. Genomic variation in Helianthus: learning from the past and looking to the future. Brief Funct Genomics 2014; 13:328-40. [DOI: 10.1093/bfgp/elu004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
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Natali L, Cossu RM, Barghini E, Giordani T, Buti M, Mascagni F, Morgante M, Gill N, Kane NC, Rieseberg L, Cavallini A. The repetitive component of the sunflower genome as shown by different procedures for assembling next generation sequencing reads. BMC Genomics 2013; 14:686. [PMID: 24093210 PMCID: PMC3852528 DOI: 10.1186/1471-2164-14-686] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Accepted: 10/03/2013] [Indexed: 11/12/2022] Open
Abstract
Background Next generation sequencing provides a powerful tool to study genome structure in species whose genomes are far from being completely sequenced. In this work we describe and compare different computational approaches to evaluate the repetitive component of the genome of sunflower, by using medium/low coverage Illumina or 454 libraries. Results By varying sequencing technology (Illumina or 454), coverage (0.55 x-1.25 x), assemblers and assembly procedures, six different genomic databases were produced. The annotation of these databases showed that they were composed of different proportions of repetitive DNA families. The final assembly of the sequences belonging to the six databases produced a whole genome set of 283,800 contigs. The redundancy of each contig was estimated by mapping the whole genome set with a large Illumina read set and measuring the number of matched Illumina reads. The repetitive component amounted to 81% of the sunflower genome, that is composed mainly of numerous families of Gypsy and Copia retrotransposons. Also many families of non autonomous retrotransposons and DNA transposons (especially of the Helitron superfamily) were identified. Conclusions The results substantially matched those previously obtained by using a Sanger-sequenced shotgun library and a standard 454 whole-genome-shotgun approach, indicating the reliability of the proposed procedures also for other species. The repetitive sequences were collected to produce a database, SUNREP, that will be useful for the annotation of the sunflower genome sequence and for studying the genome evolution in dicotyledons.
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Affiliation(s)
- Lucia Natali
- Department of Agricultural, Food, and Environmental Sciences, University of Pisa, Via del Borghetto 80, I-56124 Pisa, Italy.
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Ungerer MC, Kawakami T. Transcriptional dynamics of LTR retrotransposons in early generation and ancient sunflower hybrids. Genome Biol Evol 2013; 5:329-37. [PMID: 23335122 PMCID: PMC3590766 DOI: 10.1093/gbe/evt006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Hybridization and abiotic stress are natural agents hypothesized to influence activation and proliferation of transposable elements in wild populations. In this report, we examine the effects of these agents on expression dynamics of both quiescent and transcriptionally active sublineages of long terminal repeat (LTR) retrotransposons in wild sunflower species with a notable history of transposable element proliferation. For annual sunflower species Helianthus annuus and H. petiolaris, neither early generation hybridization nor abiotic stress, alone or in combination, induced transcriptional activation of quiescent sublineages of LTR retrotransposons. These treatments also failed to further induce expression of sublineages that are transcriptionally active; instead, expression of active sublineages in F1 and backcross hybrids was nondistinguishable from, or intermediate relative to, parental lines, and abiotic stress generally decreased normalized expression relative to controls. In contrast to findings for early generation hybridization between H. annuus and H. petiolaris, ancient sunflower hybrid species derived from these same two species and which have undergone massive proliferation events of LTR retrotransposons display 2× to 6× higher expression levels of transcriptionally active sublineages relative to parental sunflower species H. annuus and H. petiolaris. Implications and possible explanations for these findings are discussed.
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Zhang J, Long H, Pan Z, Liang J, Yu S, Deng G, Yu M. Characterization of a genome-specific Gypsy-like retrotransposon sequence and development of a molecular marker specific for Dasypyrum villosum (L.). J Genet 2013; 92:103-8. [PMID: 23640412 DOI: 10.1007/s12041-013-0218-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Jie Zhang
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, People's Republic of China
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González LG, Deyholos MK. Identification, characterization and distribution of transposable elements in the flax (Linum usitatissimum L.) genome. BMC Genomics 2012; 13:644. [PMID: 23171245 PMCID: PMC3544724 DOI: 10.1186/1471-2164-13-644] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2012] [Accepted: 11/15/2012] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Flax (Linum usitatissimum L.) is an important crop for the production of bioproducts derived from its seed and stem fiber. Transposable elements (TEs) are widespread in plant genomes and are a key component of their evolution. The availability of a genome assembly of flax (Linum usitatissimum) affords new opportunities to explore the diversity of TEs and their relationship to genes and gene expression. RESULTS Four de novo repeat identification algorithms (PILER, RepeatScout, LTR_finder and LTR_STRUC) were applied to the flax genome assembly. The resulting library of flax repeats was combined with the RepBase Viridiplantae division and used with RepeatMasker to identify TEs coverage in the genome. LTR retrotransposons were the most abundant TEs (17.2% genome coverage), followed by Long Interspersed Nuclear Element (LINE) retrotransposons (2.10%) and Mutator DNA transposons (1.99%). Comparison of putative flax TEs to flax transcript databases indicated that TEs are not highly expressed in flax. However, the presence of recent insertions, defined by 100% intra-element LTR similarity, provided evidence for recent TE activity. Spatial analysis showed TE-rich regions, gene-rich regions as well as regions with similar genes and TE density. Monte Carlo simulations for the 71 largest scaffolds (≥ 1 Mb each) did not show any regional differences in the frequency of TE overlap with gene coding sequences. However, differences between TE superfamilies were found in their proximity to genes. Genes within TE-rich regions also appeared to have lower transcript expression, based on EST abundance. When LTR elements were compared, Copia showed more diversity, recent insertions and conserved domains than the Gypsy, demonstrating their importance in genome evolution. CONCLUSIONS The calculated 23.06% TE coverage of the flax WGS assembly is at the low end of the range of TE coverages reported in other eudicots, although this estimate does not include TEs likely found in unassembled repetitive regions of the genome. Since enrichment for TEs in genomic regions was associated with reduced expression of neighbouring genes, and many members of the Copia LTR superfamily are inserted close to coding regions, we suggest Copia elements have a greater influence on recent flax genome evolution while Gypsy elements have become residual and highly mutated.
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Staton SE, Bakken BH, Blackman BK, Chapman MA, Kane NC, Tang S, Ungerer MC, Knapp SJ, Rieseberg LH, Burke JM. The sunflower (Helianthus annuus L.) genome reflects a recent history of biased accumulation of transposable elements. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2012; 72:142-53. [PMID: 22691070 DOI: 10.1111/j.1365-313x.2012.05072.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Aside from polyploidy, transposable elements are the major drivers of genome size increases in plants. Thus, understanding the diversity and evolutionary dynamics of transposable elements in sunflower (Helianthus annuus L.), especially given its large genome size (∼3.5 Gb) and the well-documented cases of amplification of certain transposons within the genus, is of considerable importance for understanding the evolutionary history of this emerging model species. By analyzing approximately 25% of the sunflower genome from random sequence reads and assembled bacterial artificial chromosome (BAC) clones, we show that it is composed of over 81% transposable elements, 77% of which are long terminal repeat (LTR) retrotransposons. Moreover, the LTR retrotransposon fraction in BAC clones harboring genes is disproportionately composed of chromodomain-containing Gypsy LTR retrotransposons ('chromoviruses'), and the majority of the intact chromoviruses contain tandem chromodomain duplications. We show that there is a bias in the efficacy of homologous recombination in removing LTR retrotransposon DNA, thereby providing insight into the mechanisms associated with transposable element (TE) composition in the sunflower genome. We also show that the vast majority of observed LTR retrotransposon insertions have likely occurred since the origin of this species, providing further evidence that biased LTR retrotransposon activity has played a major role in shaping the chromatin and DNA landscape of the sunflower genome. Although our findings on LTR retrotransposon age and structure could be influenced by the selection of the BAC clones analyzed, a global analysis of random sequence reads indicates that the evolutionary patterns described herein apply to the sunflower genome as a whole.
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Affiliation(s)
- S Evan Staton
- Department of Genetics, University of Georgia, Athens, GA 30602, USA
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Ågren JA, Wright SI. Co-evolution between transposable elements and their hosts: a major factor in genome size evolution? Chromosome Res 2012; 19:777-86. [PMID: 21850458 DOI: 10.1007/s10577-011-9229-0] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Most models of genome size evolution emphasize changes in relative rates of and/or the efficacy of selection on insertions and deletions. However, transposable elements (TEs) are a major contributor to genome size evolution, and since they experience their own selective pressures for expansion, genome size changes may in part be driven by the dynamics of co-evolution between TEs and their hosts. Under this perspective, predictions about the conditions that allow for genome expansion may be altered. In this review, we outline the evidence for TE-host co-evolution, discuss the conditions under which these dynamics can change, and explore the possible contribution to the evolution of genome size. Aided partly by advances in our understanding of the mechanisms of TE silencing via small RNAs, there is growing evidence that the evolution of transposition rates can be important in driving genome expansion and contraction. Shifts in genome size and transposon abundance associated with interspecific hybridization and changes in mating system are consistent with an important role for transposition rate evolution, although other possible explanations persist. More understanding of the potential for the breakdown of host silencing mechanisms and/or the potential for TEs to evade host immune responses will improve our understanding of the importance of changes in TE activity in driving genome size evolution.
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Affiliation(s)
- J Arvid Ågren
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S3B2, Canada
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Sun C, Shepard DB, Chong RA, López Arriaza J, Hall K, Castoe TA, Feschotte C, Pollock DD, Mueller RL. LTR retrotransposons contribute to genomic gigantism in plethodontid salamanders. Genome Biol Evol 2011; 4:168-83. [PMID: 22200636 PMCID: PMC3318908 DOI: 10.1093/gbe/evr139] [Citation(s) in RCA: 121] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/22/2011] [Indexed: 01/20/2023] Open
Abstract
Among vertebrates, most of the largest genomes are found within the salamanders, a clade of amphibians that includes 613 species. Salamander genome sizes range from ~14 to ~120 Gb. Because genome size is correlated with nucleus and cell sizes, as well as other traits, morphological evolution in salamanders has been profoundly affected by genomic gigantism. However, the molecular mechanisms driving genomic expansion in this clade remain largely unknown. Here, we present the first comparative analysis of transposable element (TE) content in salamanders. Using high-throughput sequencing, we generated genomic shotgun data for six species from the Plethodontidae, the largest family of salamanders. We then developed a pipeline to mine TE sequences from shotgun data in taxa with limited genomic resources, such as salamanders. Our summaries of overall TE abundance and diversity for each species demonstrate that TEs make up a substantial portion of salamander genomes, and that all of the major known types of TEs are represented in salamanders. The most abundant TE superfamilies found in the genomes of our six focal species are similar, despite substantial variation in genome size. However, our results demonstrate a major difference between salamanders and other vertebrates: salamander genomes contain much larger amounts of long terminal repeat (LTR) retrotransposons, primarily Ty3/gypsy elements. Thus, the extreme increase in genome size that occurred in salamanders was likely accompanied by a shift in TE landscape. These results suggest that increased proliferation of LTR retrotransposons was a major molecular mechanism contributing to genomic expansion in salamanders.
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Affiliation(s)
- Cheng Sun
- Department of Biology, Colorado State University
| | - Donald B. Shepard
- Department of Biology, Colorado State University
- Current address: Department of Fisheries, Wildlife and Conservation Biology; University of Minnesota
| | | | | | - Kathryn Hall
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine
| | - Todd A. Castoe
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine
| | | | - David D. Pollock
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine
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Kawakami T, Dhakal P, Katterhenry AN, Heatherington CA, Ungerer MC. Transposable element proliferation and genome expansion are rare in contemporary sunflower hybrid populations despite widespread transcriptional activity of LTR retrotransposons. Genome Biol Evol 2011; 3:156-67. [PMID: 21282712 PMCID: PMC3048363 DOI: 10.1093/gbe/evr005] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Hybridization is a natural phenomenon that has been linked in several organismal groups to transposable element derepression and copy number amplification. A noteworthy example involves three diploid annual sunflower species from North America that have arisen via ancient hybridization between the same two parental taxa, Helianthus annuus and H. petiolaris. The genomes of the hybrid species have undergone large-scale increases in genome size attributable to long terminal repeat (LTR) retrotransposon proliferation. The parental species that gave rise to the hybrid taxa are widely distributed, often sympatric, and contemporary hybridization between them is common. Natural H. annuus × H. petiolaris hybrid populations likely served as source populations from which the hybrid species arose and, as such, represent excellent natural experiments for examining the potential role of hybridization in transposable element derepression and proliferation in this group. In the current report, we examine multiple H. annuus × H. petiolaris hybrid populations for evidence of genome expansion, LTR retrotransposon copy number increases, and LTR retrotransposon transcriptional activity. We demonstrate that genome expansion and LTR retrotransposon proliferation are rare in contemporary hybrid populations, despite independent proliferation events that took place in the genomes of the ancient hybrid species. Interestingly, LTR retrotransposon lineages that proliferated in the hybrid species genomes remain transcriptionally active in hybrid and nonhybrid genotypes across the entire sampling area. The finding of transcriptional activity but not copy number increases in hybrid genotypes suggests that proliferation and genome expansion in contemporary hybrid populations may be mitigated by posttranscriptional mechanisms of repression.
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Fat element—a new marker for chromosome and genome analysis in the Triticeae. Chromosome Res 2010; 18:697-709. [DOI: 10.1007/s10577-010-9151-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2010] [Revised: 07/05/2010] [Accepted: 07/29/2010] [Indexed: 10/19/2022]
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Abstract
Genome sizes vary considerably across all eukaryotes and even among closely related species. The genesis and evolutionary dynamics of that variation have generated considerable interest, as have the patterns of variation themselves. Here we review recent developments in our understanding of genome size evolution in plants, drawing attention to the higher order processes that can influence the mechanisms generating changing genome size.
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Kawakami T, Strakosh SC, Zhen Y, Ungerer MC. Different scales of Ty1/copia-like retrotransposon proliferation in the genomes of three diploid hybrid sunflower species. Heredity (Edinb) 2010; 104:341-50. [PMID: 20068588 DOI: 10.1038/hdy.2009.182] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Activation of transposable elements in species' genomes represents an important mechanism of new mutation and of potential rapid change in genome size. Thus, it is increasingly recognized that transposable elements likely have played a significant role in shaping species' evolution. In an earlier report, we showed that the genomes of three sunflower species of ancient hybrid origin have experienced large-scale proliferation events of sequences within the Ty3/gypsy-like superfamily of long terminal repeat (LTR) retrotransposons. In this report, we investigate whether another superfamily of LTR retrotransposon (Ty1/copia-like elements) have experienced similar derepression and proliferation events in the genomes of these sunflower hybrid taxa. We show that Ty1/copia-like elements also have undergone copy number increases following or associated with the origins of these species, although the scale of proliferation is less than that for Ty3/gypsy-like elements. Surveys of sequence heterogeneity of Ty1/copia-like elements in the genomes of the three hybrid and two parental species' genomes reveal that a single sub-lineage of these elements exhibits characteristics of recent amplification, and likely served as the proliferative source lineage. These findings indicate that the genomic and/or environmental conditions associated with the origins of these sunflower hybrid taxa were conducive to derepression of at least two major groups of transposable elements.
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Affiliation(s)
- T Kawakami
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
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Ungerer MC, Strakosh SC, Stimpson KM. Proliferation of Ty3/gypsy-like retrotransposons in hybrid sunflower taxa inferred from phylogenetic data. BMC Biol 2009; 7:40. [PMID: 19594956 PMCID: PMC2715380 DOI: 10.1186/1741-7007-7-40] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Accepted: 07/14/2009] [Indexed: 11/13/2022] Open
Abstract
Background Long terminal repeat (LTR) retrotransposons are a class of mobile genetic element capable of autonomous transposition via an RNA intermediate. Their large size and proliferative ability make them important contributors to genome size evolution, especially in plants, where they can reach exceptionally high copy numbers and contribute substantially to variation in genome size even among closely related taxa. Using a phylogenetic approach, we characterize dynamics of proliferation events of Ty3/gypsy-like LTR retrotransposons that led to massive genomic expansion in three Helianthus (sunflower) species of ancient hybrid origin. The three hybrid species are independently derived from the same two parental species, offering a unique opportunity to explore patterns of retrotransposon proliferation in light of reticulate evolutionary events in this species group. Results We demonstrate that Ty3/gypsy-like retrotransposons exist as multiple well supported sublineages in both the parental and hybrid derivative species and that the same element sublineage served as the source lineage of proliferation in each hybrid species' genome. This inference is based on patterns of species-specific element numerical abundance within different phylogenetic sublineages as well as through signals of proliferation events present in the distributions of element divergence values. Employing methods to date paralogous sequences within a genome, proliferation events in the hybrid species' genomes are estimated to have occurred approximately 0.5 to 1 million years ago. Conclusion Proliferation of the same retrotransposon major sublineage in each hybrid species indicates that similar dynamics of element derepression and amplification likely occurred in each hybrid taxon during their formation. Temporal estimates of these proliferation events suggest an earlier origin for these hybrid species than previously supposed.
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Affiliation(s)
- Mark C Ungerer
- Division of Biology, Kansas State University, Manhattan, Kansas, USA.
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