Abstract
BACKGROUND: Chromatin organizational and topological plasticity, and its functions in gene expression regulation, have been strongly revealed by the analysis of nucleolar dominance in hybrids and polyploids where one parental set of ribosomal RNA (rDNA) genes that are clustered in nucleolar organizing regions (NORs), is rendered silent by epigenetic pathways and heterochromatization. However, information on the behaviour of dominant NORs is very sparse and needed for an integrative knowledge of differential gene transcription levels and chromatin specific domain interactions. METHODOLOGY/PRINCIPAL FINDINGS: Using molecular and cytological approaches in a wheat-rye addition line (wheat genome plus the rye nucleolar chromosome pair 1R), we investigated transcriptional activity and chromatin topology of the wheat dominant NORs in a nucleolar dominance situation. Herein we report dominant NORs up-regulation in the addition line through quantitative real-time PCR and silver-staining technique. Accompanying this modification in wheat rDNA trascription level, we also disclose that perinucleolar knobs of ribosomal chromatin are almost transcriptionally silent due to the residual detection of BrUTP incorporation in these domains, contrary to the marked labelling of intranucleolar condensed rDNA. Further, by comparative confocal analysis of nuclei probed to wheat and rye NORs, we found that in the wheat-rye addition line there is a significant decrease in the number of wheat-origin perinucleolar rDNA knobs, corresponding to a diminution of the rDNA heterochromatic fraction of the dominant (wheat) NORs. CONCLUSIONS/SIGNIFICANCE: We demonstrate that inter-specific interactions leading to wheat-origin NOR dominance results not only on the silencing of rye origin NOR loci, but dominant NORs are also modified in their transcriptional activity and interphase organization. The results show a cross-talk between wheat and rye NORs, mediated by ribosomal chromatin dynamics, revealing a conceptual shift from differential amphiplasty to 'mutual amphiplasty' in the nucleolar dominance process.
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Claims 6
Claim · model-written summary
Dominant wheat NORs were up-regulated in the wheat-rye addition line.
Verbatim
e0“Herein we report dominant NORs up-regulation in the addition line through quantitative real-time PCR and silver-staining technique.”
t0“Wheat-Rye System”
Claim · model-written summary
Perinucleolar ribosomal chromatin knobs were nearly transcriptionally silent, unlike intranucleolar condensed rDNA.
Verbatim
e0“perinucleolar knobs of ribosomal chromatin are almost transcriptionally silent due to the residual detection of BrUTP incorporation in these domains, contrary to the marked labelling of intranucleolar condensed rDNA.”
t0“Wheat-Rye System”
Claim · model-written summary
The wheat-rye addition line had significantly fewer wheat-origin perinucleolar rDNA knobs.
Verbatim
e0“in the wheat-rye addition line there is a significant decrease in the number of wheat-origin perinucleolar rDNA knobs”
Claim · model-written summary
The heterochromatic fraction of dominant wheat NORs diminished in the addition line.
Verbatim
e0“corresponding to a diminution of the rDNA heterochromatic fraction of the dominant (wheat) NORs.”
t0“Wheat-Rye System”
Claim · model-written summary
Rye-origin NOR loci were silenced in the nucleolar dominance interaction.
- Taxon
- rye
Secale cerealee0 - Gene
- rye origin NOR locie0
- Outcome
- silencing of rye origin NOR locie0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“inter-specific interactions leading to wheat-origin NOR dominance results not only on the silencing of rye origin NOR loci, but dominant NORs are also modified in their transcriptional activity and interphase organization.”
Claim · model-written summary
Dominant wheat NORs changed in transcriptional activity and interphase organization.
Verbatim
e0“dominant NORs are also modified in their transcriptional activity and interphase organization.”
t0“Wheat-Rye System”