Asymmetric Epigenetic Modification and Elimination of rDNA Sequences by Polyploidization in Wheat

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 re...

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Bibliographic Details
Published inThe Plant cell Vol. 26; no. 11; pp. 4311 - 4327
Main Authors Guo, Xiang, Han, Fangpu
Format Journal Article
LanguageEnglish
Published United States American Society of Plant Biologists 01.11.2014
Subjects
Allopolyploidy
Base Sequence
Chromosomes
DNA
DNA Methylation
DNA, Plant - genetics
DNA, Ribosomal - genetics
Epigenesis, Genetic
Evolution, Molecular
Genetic loci
Genetic Loci - genetics
Genome, Plant - genetics
Genomes
Histones - genetics
Hybridization, Genetic
Internal transcribed spacers
Methylation
Molecular Sequence Data
Nucleolus Organizer Region
Polyploidy
Ribosomal DNA
rRNA genes
Sequence Analysis, DNA
Triticum - genetics
Triticum aestivum
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Summary: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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www.plantcell.org/cgi/doi/10.1105/tpc.114.129841
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Fangpu Han (fphan@genetics.ac.cn).
ISSN:1040-4651
1532-298X
DOI:10.1105/tpc.114.129841