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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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Appels R, Wang P, Islam S. Integrating Wheat Nucleolus Structure and Function: Variation in the Wheat Ribosomal RNA and Protein Genes. FRONTIERS IN PLANT SCIENCE 2021; 12:686586. [PMID: 35003148 PMCID: PMC8739226 DOI: 10.3389/fpls.2021.686586] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2021] [Accepted: 11/08/2021] [Indexed: 06/13/2023]
Abstract
We review the coordinated production and integration of the RNA (ribosomal RNA, rRNA) and protein (ribosomal protein, RP) components of wheat cytoplasmic ribosomes in response to changes in genetic constitution, biotic and abiotic stresses. The components examined are highly conserved and identified with reference to model systems such as human, Arabidopsis, and rice, but have sufficient levels of differences in their DNA and amino acid sequences to form fingerprints or gene haplotypes that provide new markers to associate with phenotype variation. Specifically, it is argued that populations of ribosomes within a cell can comprise distinct complements of rRNA and RPs to form units with unique functionalities. The unique functionalities of ribosome populations within a cell can become central in situations of stress where they may preferentially translate mRNAs coding for proteins better suited to contributing to survival of the cell. In model systems where this concept has been developed, the engagement of initiation factors and elongation factors to account for variation in the translation machinery of the cell in response to stresses provided the precedents. The polyploid nature of wheat adds extra variation at each step of the synthesis and assembly of the rRNAs and RPs which can, as a result, potentially enhance its response to changing environments and disease threats.
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Affiliation(s)
- Rudi Appels
- AgriBio, Centre for AgriBioscience, La Trobe University, Bundoora, VIC, Australia
- Faculty of Veterinary and Agricultural Science, Melbourne, VIC, Australia
| | - Penghao Wang
- School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, Australia
| | - Shahidul Islam
- Centre for Crop Innovation, Food Futures Institute, Murdoch University, Murdoch, WA, Australia
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Current Progress in Understanding and Recovering the Wheat Genes Lost in Evolution and Domestication. Int J Mol Sci 2020; 21:ijms21165836. [PMID: 32823887 PMCID: PMC7461589 DOI: 10.3390/ijms21165836] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 08/08/2020] [Accepted: 08/12/2020] [Indexed: 01/19/2023] Open
Abstract
The modern cultivated wheat has passed a long evolution involving origin of wild emmer (WEM), development of cultivated emmer, formation of spelt wheat and finally establishment of modern bread wheat and durum wheat. During this evolutionary process, rapid alterations and sporadic changes in wheat genome took place, due to hybridization, polyploidization, domestication, and mutation. This has resulted in some modifications and a high level of gene loss. As a result, the modern cultivated wheat does not contain all genes of their progenitors. These lost genes are novel for modern wheat improvement. Exploring wild progenitor for genetic variation of important traits is directly beneficial for wheat breeding. WEM wheat (Triticum dicoccoides) is a great genetic resource with huge diversity for traits. Few genes and quantitative trait loci (QTL) for agronomic, quantitative, biotic and abiotic stress-related traits have already been mapped from WEM. This resource can be utilized for modern wheat improvement by integrating identified genes or QTLs through breeding.
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Matyášek R, Kuderová A, Kutílková E, Kučera M, Kovařík A. Intragenomic heterogeneity of intergenic ribosomal DNA spacers in Cucurbita moschata is determined by DNA minisatellites with variable potential to form non-canonical DNA conformations. DNA Res 2019; 26:273-286. [PMID: 31231763 PMCID: PMC6589552 DOI: 10.1093/dnares/dsz008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 04/03/2019] [Indexed: 11/26/2022] Open
Abstract
The intergenic spacer (IGS) of rDNA is frequently built of long blocks of tandem repeats. To estimate the intragenomic variability of such knotty regions, we employed PacBio sequencing of the Cucurbita moschata genome, in which thousands of rDNA copies are distributed across a number of loci. The rRNA coding regions are highly conserved, indicating intensive interlocus homogenization and/or high selection pressure. However, the IGS exhibits high intragenomic structural diversity. Two repeated blocks, R1 (300-1250 bp) and R2 (290-643 bp), account for most of the IGS variation. They exhibit minisatellite-like features built of multiple periodically spaced short GC-rich sequence motifs with the potential to adopt non-canonical DNA conformations, G-quadruplex-folded and left-handed Z-DNA. The mutual arrangement of these motifs can be used to classify IGS variants into five structural families. Subtle polymorphisms exist within each family due to a variable number of repeats, suggesting the coexistence of an enormous number of IGS variants. The substantial length and structural heterogeneity of IGS minisatellites suggests that the tempo of their divergence exceeds the tempo of the homogenization of rDNA arrays. As frequently occurring among plants, we hypothesize that their instability may influence transcription regulation and/or destabilize rDNA units, possibly spreading them across the genome.
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Affiliation(s)
- Roman Matyášek
- Institute of Biophysics of the Czech Academy of Sciences, CZ Brno, Czech Republic
| | - Alena Kuderová
- Institute of Biophysics of the Czech Academy of Sciences, CZ Brno, Czech Republic
| | - Eva Kutílková
- Institute of Biophysics of the Czech Academy of Sciences, CZ Brno, Czech Republic
| | - Marek Kučera
- Institute of Biophysics of the Czech Academy of Sciences, CZ Brno, Czech Republic
| | - Aleš Kovařík
- Institute of Biophysics of the Czech Academy of Sciences, CZ Brno, Czech Republic
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Relationship between epigenetic marks and the behavior of 45S rDNA sites in chromosomes and interphase nuclei of Lolium-Festuca complex. Mol Biol Rep 2018; 45:1663-1679. [PMID: 30121822 DOI: 10.1007/s11033-018-4310-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 08/14/2018] [Indexed: 10/28/2022]
Abstract
The grasses of the Lolium-Festuca complex show a prominent role in world agricultural scenario. Several studies have demonstrated that the plasticity of 45S rDNA sites has been recently associated with the possible fragility of the loci. Often, these fragile sites were observed as extended sites and gaps in metaphases. This organization can be evaluated in relation to their transcriptional activity/accessibility through epigenetic changes. Thus, this study aimed to investigate the relationship of the 5-methylcytosine and histone H3 lysine-9 dimethylation in different conformations of 45S rDNA sites in interphase nuclei and in metaphase chromosomes of L. perenne, L. multiflorum and F. arundinacea. The FISH technique using 45S rDNA probes was performed sequentially after the immunolocalization. The sites showed predominantly the following characteristics in the interphase nuclei: intra- and perinucleolar position, decondensed or partially condensed and hypomethylated and hyper/hypomethylated status. Extranucleolar sites were mainly hypermethylated for both epigenetic marks. The 45S rDNA sites with gaps identified in metaphases were always hypomethylated, which justifies it decondensed and transcriptional state. The frequency of sites with hypermethylated gaps was very low. The structural differences observed in these sites are directly related to the assessed epigenetic marks, justifying the different conformations throughout the cell cycle.
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Inácio V, Martins MT, Graça J, Morais-Cecílio L. Cork Oak Young and Traumatic Periderms Show PCD Typical Chromatin Patterns but Different Chromatin-Modifying Genes Expression. FRONTIERS IN PLANT SCIENCE 2018; 9:1194. [PMID: 30210513 PMCID: PMC6120546 DOI: 10.3389/fpls.2018.01194] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 07/25/2018] [Indexed: 05/20/2023]
Abstract
Plants are subjected to adverse conditions being outer protective tissues fundamental to their survival. Tree stems are enveloped by a periderm made of cork cells, resulting from the activity of the meristem phellogen. DNA methylation and histone modifications have important roles in the regulation of plant cell differentiation. However, studies on its involvement in cork differentiation are scarce despite periderm importance. Cork oak periderm development was used as a model to study the formation and differentiation of secondary protective tissues, and their behavior after traumatic wounding (traumatic periderm). Nuclei structural changes, dynamics of DNA methylation, and posttranslational histone modifications were assessed in young and traumatic periderms, after cork harvesting. Lenticular phellogen producing atypical non-suberized cells that disaggregate and form pores was also studied, due to high impact for cork industrial uses. Immunolocalization of active and repressive marks, transcription analysis of the corresponding genes, and correlations between gene expression and cork porosity were investigated. During young periderm development, a reduction in nuclei area along with high levels of DNA methylation occurred throughout epidermis disruption. As cork cells became more differentiated, whole nuclei progressive chromatin condensation with accumulation in the nuclear periphery and increasing DNA methylation was observed. Lenticular cells nuclei were highly fragmented with faint 5-mC labeling. Phellogen nuclei were less methylated than in cork cells, and in lenticular phellogen were even lower. No significant differences were detected in H3K4me3 and H3K18ac signals between cork cells layers, although an increase in H3K4me3 signals was found from the phellogen to cork cells. Distinct gene expression patterns in young and traumatic periderms suggest that cork differentiation might be under specific silencing regulatory pathways. Significant correlations were found between QsMET1, QsMET2, and QsSUVH4 gene expression and cork porosity. This work evidences that DNA methylation and histone modifications play a role in cork differentiation and epidermis induced tension-stress. It also provides the first insights into chromatin dynamics during cork and lenticular cells differentiation pointing to a distinct type of remodeling associated with cell death.
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Affiliation(s)
- Vera Inácio
- Linking Landscape, Environment, Agriculture and Food (LEAF), Institute of Agronomy, University of Lisbon, Lisbon, Portugal
- *Correspondence: Vera Inácio,
| | - Madalena T. Martins
- Linking Landscape, Environment, Agriculture and Food (LEAF), Institute of Agronomy, University of Lisbon, Lisbon, Portugal
| | - José Graça
- Forest Research Center (CEF), Institute of Agronomy, University of Lisbon, Lisbon, Portugal
| | - Leonor Morais-Cecílio
- Linking Landscape, Environment, Agriculture and Food (LEAF), Institute of Agronomy, University of Lisbon, Lisbon, Portugal
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Borowska-Zuchowska N, Hasterok R. Epigenetics of the preferential silencing of Brachypodium stacei-originated 35S rDNA loci in the allotetraploid grass Brachypodium hybridum. Sci Rep 2017; 7:5260. [PMID: 28706212 PMCID: PMC5509716 DOI: 10.1038/s41598-017-05413-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 05/30/2017] [Indexed: 01/16/2023] Open
Abstract
Nucleolar dominance (ND), initially described as ‘differential amphiplasty’, is a phenomenon observed in some plant and animal allopolyploids and hybrids in which the selective suppression of the activity of 35S rRNA gene loci that have been inherited from one of the two or more ancestral genomes occurs. Although more than 80 years have passed since the discovery of ND, there is still a significant lack in our understanding of the mechanisms that determine this phenomenon. Here, we aimed to investigate the epigenetic status of 35S rRNA gene loci in the monocotyledonous Brachypodium hybridum, which is an allotetraploid that has resulted from a cross between B. distachyon and B. stacei. We revealed that the repressed B. stacei-inherited rDNA loci are characterised by a high level of DNA methylation. The global hypomethylation of B. hybridum nuclear DNA induced by 5-azacytidine, however, seems to be insufficient for the transcriptional reactivation of these loci, which indicates that factors other than DNA methylation are behind the suppression of B. stacei-originated loci. We also showed that the transcriptionally active and silenced fractions of rRNA genes that had been inherited from B. distachyon occupy different domains within the chromocentres adjacent to the nucleolus, depending on their epigenetic status.
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Affiliation(s)
- Natalia Borowska-Zuchowska
- Department of Plant Anatomy and Cytology, Faculty of Biology and Environmental Protection, University of Silesia in Katowice, 28 Jagiellonska Street, 40-032, Katowice, Poland.
| | - Robert Hasterok
- Department of Plant Anatomy and Cytology, Faculty of Biology and Environmental Protection, University of Silesia in Katowice, 28 Jagiellonska Street, 40-032, Katowice, Poland
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Santos AP, Ferreira LJ, Oliveira MM. Concerted Flexibility of Chromatin Structure, Methylome, and Histone Modifications along with Plant Stress Responses. BIOLOGY 2017; 6:biology6010003. [PMID: 28275209 PMCID: PMC5371996 DOI: 10.3390/biology6010003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 01/05/2017] [Accepted: 01/10/2017] [Indexed: 12/12/2022]
Abstract
The spatial organization of chromosome structure within the interphase nucleus, as well as the patterns of methylome and histone modifications, represent intersecting layers that influence genome accessibility and function. This review is focused on the plastic nature of chromatin structure and epigenetic marks in association to stress situations. The use of chemical compounds (epigenetic drugs) or T-DNA-mediated mutagenesis affecting epigenetic regulators (epi-mutants) are discussed as being important tools for studying the impact of deregulated epigenetic backgrounds on gene function and phenotype. The inheritability of epigenetic marks and chromatin configurations along successive generations are interpreted as a way for plants to “communicate” past experiences of stress sensing. A mechanistic understanding of chromatin and epigenetics plasticity in plant response to stress, including tissue- and genotype-specific epigenetic patterns, may help to reveal the epigenetics contributions for genome and phenotype regulation.
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Affiliation(s)
- Ana Paula Santos
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Genomics of Plant Stress Unit. Av. da República, 2780-157 Oeiras, Portugal.
| | - Liliana J Ferreira
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Genomics of Plant Stress Unit. Av. da República, 2780-157 Oeiras, Portugal.
| | - M Margarida Oliveira
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Genomics of Plant Stress Unit. Av. da República, 2780-157 Oeiras, Portugal.
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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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Guo X, Han F. Asymmetric epigenetic modification and elimination of rDNA sequences by polyploidization in wheat. THE PLANT CELL 2014; 26:4311-27. [PMID: 25415973 PMCID: PMC4277213 DOI: 10.1105/tpc.114.129841] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
rRNA genes consist of long tandem repeats clustered on chromosomes, and their products are important functional components of the ribosome. In common wheat (Triticum aestivum), rDNA loci from the A and D genomes were largely lost during the evolutionary process. This biased DNA elimination may be related to asymmetric transcription and epigenetic modifications caused by the polyploid formation. Here, we observed both sets of parental nucleolus organizing regions (NORs) were expressed after hybridization, but asymmetric silencing of one parental NOR was immediately induced by chromosome doubling, and reversing the ploidy status could not reactivate silenced NORs. Furthermore, increased CHG and CHH DNA methylation on promoters was accompanied by asymmetric silencing of NORs. Enrichment of H3K27me3 and H3K9me2 modifications was also observed to be a direct response to increased DNA methylation and transcriptional inactivation of NOR loci. Both A and D genome NOR loci with these modifications started to disappear in the S4 generation and were completely eliminated by the S7 generation in synthetic tetraploid wheat. Our results indicated that asymmetric epigenetic modification and elimination of rDNA sequences between different donor genomes may lead to stable allopolyploid wheat with increased differentiation and diversity.
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Affiliation(s)
- Xiang Guo
- State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fangpu Han
- State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
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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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PI3K is involved in nucleolar structure and function on root-tip meristematic cells of Triticum aestivum L. Acta Histochem 2014; 116:838-43. [PMID: 24642039 DOI: 10.1016/j.acthis.2014.02.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2013] [Revised: 02/05/2014] [Accepted: 02/06/2014] [Indexed: 11/20/2022]
Abstract
In this study, wheat (Triticum aestivum L.) seeds were used to detect the effect of wortmannin, a specific inhibitor of PI3K, on the nucleolar structure and function. When the germinated seeds were treated with wortmannin, it was shown that the root growth was suppressed and the mitotic index was decreased. The inhibition effects were positively correlated with the concentrations of the drug. The observations of light and transmission electron microscopy revealed that the nucleolar morphology became irregular and their fine structure disappeared. Some granules with a size range of 0.05-0.30 μm diffused from the nucleoli and gradually moved to the nucleoplasm between or around the chromatin. Indirect immunofluorescence staining indicated that B23 shuttled from the nucleoli to the nucleoplasm, or even, to the cytoplasm. RT-PCR technique demonstrated that the expression of C23 was severely down-regulated. Our results suggest, for the first time, that wortmannin treatment can not only damage nucleolar structure, but also inhibit its function, implying that PI3K is involved in nucleolar structure and function.
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Tomás D, Brazão J, Viegas W, Silva M. Differential Effects of High-Temperature Stress on Nuclear Topology and Transcription of Repetitive Noncoding and Coding Rye Sequences. Cytogenet Genome Res 2012; 139:119-27. [DOI: 10.1159/000343754] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/16/2012] [Indexed: 12/25/2022] Open
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15
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Physical localization of NORs and ITS length variants in old Portuguese durum wheat cultivars. J Genet 2011; 90:95-101. [PMID: 21677393 DOI: 10.1007/s12041-011-0033-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The variation at the internal transcribed spacer (ITS) region of the ribosomal DNA has been correlated with the number of nucleolar organizer regions (NORs) in some plant species. Besides, the number of NORs might influence the rate of homogenization of the rDNA repeats. In recent studies, ITS length variants were detected in bread wheat cultivars but no reports about their presence in durum wheat were found. In the present study, we localized and identified the NORs of 51 old Portuguese durum wheat cultivars by using sequential silver staining and fluorescence in situ hybridization performed with the pTa71 rDNA probe. We also detected ITS length variants by PCR-RFLP. No variation at the number of Ag-NORs per metaphase was found among the 51 durum wheat cultivars, but the PCR-RFLP technique carried out with the restriction enzyme HpaII, allowed the detection of ITS length variants among them. The molecular data was used in order to establish the genetic relationships among cultivars and botanical varieties of durum wheat. The knowledge of this feature could be useful for future design of breeding strategies, involving this collection that constitutes an excellent repository of germplasm in Portugal.
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Santos A, Ferreira L, Maroco J, Oliveira M. Abiotic Stress and Induced DNA Hypomethylation Cause Interphase Chromatin Structural Changes in Rice rDNA Loci. Cytogenet Genome Res 2011; 132:297-303. [DOI: 10.1159/000322287] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/07/2010] [Indexed: 01/30/2023] Open
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Bento M, Gustafson P, Viegas W, Silva M. Genome merger: from sequence rearrangements in triticale to their elimination in wheat-rye addition lines. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2010; 121:489-497. [PMID: 20383487 DOI: 10.1007/s00122-010-1325-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2009] [Accepted: 03/12/2010] [Indexed: 05/29/2023]
Abstract
Genetic and epigenetic modifications resulting from different genomes adjusting to a common nuclear environment have been observed in polyploids. Sequence restructuring within genomes involving retrotransposon/microsatellite-rich regions has been reported in triticale. The present study uses inter-retrotransposon amplified polymorphisms (IRAP) and retrotransposon microsatellite amplified polymorphisms (REMAP) to assess genome rearrangements in wheat-rye addition lines obtained by the controlled backcrossing of octoploid triticale to hexaploid wheat followed by self-fertilization. The comparative analysis of IRAP and REMAP banding profiles, involving a complete set of wheat-rye addition lines, and their parental species revealed in those lines the presence of wheat-origin bands absent in triticale, and the absence of rye-origin and triticale-specific bands. The presence in triticale x wheat backcrosses (BC) of rye-origin bands that were absent in the addition lines demonstrated that genomic rearrangement events were not a direct consequence of backcrossing, but resulted from further genome structural rearrangements in the BC plant progeny. PCR experiments using primers designed from different rye-origin sequences showed that the absence of a rye-origin band in wheat-rye addition lines results from sequence elimination rather than restrict changes on primer annealing sites, as noted in triticale. The level of genome restructuring events evaluated in all seven wheat-rye addition lines, compared to triticale, indicated that the unbalanced genome merger situation observed in the addition lines induced a new round of genome rearrangement, suggesting that the lesser the amount of rye chromatin introgressed into wheat the larger the outcome of genome reshuffling.
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Affiliation(s)
- Miguel Bento
- Centro de Botânica Aplicada à Agricultura, Secção de Genética, Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1349-017, Lisbon, Portugal
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Tucker S, Vitins A, Pikaard CS. Nucleolar dominance and ribosomal RNA gene silencing. Curr Opin Cell Biol 2010; 22:351-6. [PMID: 20392622 DOI: 10.1016/j.ceb.2010.03.009] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Accepted: 03/22/2010] [Indexed: 12/11/2022]
Abstract
Nucleolar dominance is an epigenetic phenomenon that occurs in genetic hybrids and describes the expression of 45S rRNA genes inherited from one progenitor due to the silencing of the other progenitor's rRNA genes. Nucleolar dominance is a manifestation of rRNA gene dosage control, which also occurs in non-hybrids, regulating the number of active rRNA genes according to the cellular demand for ribosomes and protein synthesis. Ribosomal RNA gene silencing involves changes in DNA methylation and histone modifications, but the molecular basis for choosing which genes to silence remains unclear. Recent studies indicate a role for short interfering RNAs (siRNAs) or structured regulatory RNAs in rRNA gene silencing in plants or mammals, respectively, suggesting that RNA may impart specificity to the choice mechanism.
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Affiliation(s)
- Sarah Tucker
- Department of Biology, Washington University, St. Louis, MO 63130, USA
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