Genes encoding ribosomal RNA (rDNA) are essential for cell survival and are particularly sensitive to factors leading to genomic instability. Their repetitive character makes them prone to inappropriate recombinational events arising from collision of transcriptional and replication machineries, resulting in unstable rDNA copy numbers. In this review, we summarize current knowledge on the structure and organization of rDNA, its role in sensing changes in the genome, and its linkage to aging. We also review recent findings on the main factors involved in chromatin assembly and DNA repair in the maintenance of rDNA stability in the model plants Arabidopsis thaliana and the moss Physcomitrella patens, providing a view across the plant evolutionary tree.

• Klíčová slova
• CAF-1, RAD51, RTEL1, genome stability, rDNA organization, rRNA genes, ribosome,
• MeSH
• Arabidopsis genetika   MeSH
• DNA rostlinná genetika   MeSH
• genetická transkripce MeSH
• genová dávka MeSH
• lidé MeSH
• mechy genetika   MeSH
• nestabilita genomu MeSH
• oprava DNA * MeSH
• replikace DNA MeSH
• restrukturace chromatinu MeSH
• ribozomální DNA genetika   MeSH
• stárnutí genetika   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• DNA rostlinná MeSH
• ribozomální DNA MeSH

Arabidopsis thaliana mutants in FAS1 and FAS2 subunits of chromatin assembly factor 1 (CAF1) show progressive loss of 45S rDNA copies and telomeres. We hypothesized that homology-dependent DNA damage repair (HDR) may contribute to the loss of these repeats in fas mutants. To test this, we generated double mutants by crossing fas mutants with knock-out mutants in RAD51B, one of the Rad51 paralogs of A. thaliana. Our results show that the absence of RAD51B decreases the rate of rDNA loss, confirming the implication of RAD51B-dependent recombination in rDNA loss in the CAF1 mutants. Interestingly, this effect is not observed for telomeric repeat loss, which thus differs from that acting in rDNA loss. Involvement of DNA damage repair in rDNA dynamics in fas mutants is further supported by accumulation of double-stranded breaks (measured as γ-H2AX foci) in 45S rDNA. Occurrence of the foci is not specific for S-phase, and is ATM-independent. While the foci in fas mutants occur both in the transcribed (intranucleolar) and non-transcribed (nucleoplasmic) fraction of rDNA, double fas rad51b mutants show a specific increase in the number of the intranucleolar foci. These results suggest that the repair of double-stranded breaks present in the transcribed rDNA region is RAD51B dependent and that this contributes to rDNA repeat loss in fas mutants, presumably via the single-stranded annealing recombination pathway. Our results also highlight the importance of proper chromatin assembly in the maintenance of genome stability.

• Klíčová slova
• 45S rDNA, Arabidopsis thaliana, DNA repair, FAS1, FAS2, RAD51B, chromatin assembly factor 1, genome instability,
• MeSH
• Arabidopsis genetika   metabolismus   MeSH
• faktor 1 pro uspořádání chromatinu genetika   metabolismus   MeSH
• nestabilita genomu genetika   fyziologie   MeSH
• oprava DNA genetika   fyziologie   MeSH
• proteiny huseníčku genetika   metabolismus   MeSH
• ribozomální DNA genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• faktor 1 pro uspořádání chromatinu MeSH
• FAS protein, Arabidopsis MeSH Prohlížeč
• proteiny huseníčku MeSH
• RAD51B protein, Arabidopsis MeSH Prohlížeč
• ribozomální DNA MeSH