Restricted chromosomal silencing in nucleolar dominance
1Biology Department, Washington University, Campus Box 1137, One Brookings Drive, St. Louis, MO 63130, USA.
Summary
Nucleolar dominance silences most of the Arabidopsis thaliana nucleolus organizer regions (NORs) in the hybrid Arabidopsis suecica. Genes near silenced NORs remain active, suggesting targeted epigenetic regulation of rRNA genes.
Area of Science:
- Epigenetics
- Genomics
- Plant Biology
Background:
- Nucleolar dominance is an epigenetic phenomenon where one parent's chromosomes fail to organize nucleoli in interspecific hybrids.
- This involves large-scale gene silencing, but the full extent of inactivation beyond nucleolus organizer regions (NORs) is not well understood.
Purpose of the Study:
- To map the extent of nucleolar dominance-induced silencing in the allotetraploid hybrid Arabidopsis suecica.
- To investigate whether silencing spreads from NORs to adjacent chromosomal regions.
Main Methods:
- Utilized genome sequence data for Arabidopsis thaliana.
- Employed a sensitive reverse transcription PCR assay to quantify gene silencing.
- Mapped the extent of silencing in Arabidopsis suecica vegetative leaves.
Main Results:
- Four A. thaliana NORs (approx. 4 Mbp each) were found to be ~99.5% silenced in A. suecica leaves.
- NORs inherited from Arabidopsis arenosa remained fully active.
- Protein-coding genes located very close (as near as 3.1 kb) to silenced A. thaliana NORs were actively transcribed.
Conclusions:
- The findings challenge hypotheses suggesting silencing spreads from adjacent chromosomal regions.
- Data support models where epigenetic regulation specifically targets NORs or rRNA genes.
- This provides a detailed map of epigenetic silencing at NORs in an interspecific hybrid.
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