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.

Chromatin Molecular Complexes Mendel Centre for Plant Genomics and Proteomics Central European Institute of Technology Masaryk University CZ 62500 Brno Czech Republic

Department of Cell Biology and Radiobiology Institute of Biophysics of the Czech Academy of Sciences CZ 61265 Brno Czech Republic

Laboratory of Functional Genomics and Proteomics National Centre for Biomolecular Research Faculty of Science Masaryk University CZ 61137 Brno Czech Republic

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