Abstract
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.
Highlights
Translation, the rewriting of a sequence of nucleotides from mRNA into a chain of amino acids forming a protein, is an essential and fascinating process in a cell’s life as most biological activities are performed by proteins
The huge profusion of ribosomal RNA (rRNA) gene copies in plants plays an important role in the maintenance of genomic stability because, under the pressure of adverse changes in various genetic or epigenetic factors, the cell reacts to the situation by a change in rDNA copy number
The demand for extensive transcription of rDNA needed for ribosome biogenesis throughout the cell cycle requires changes in the nuclear architecture that enables genome replication
Summary
Translation, the rewriting of a sequence of nucleotides from mRNA into a chain of amino acids forming a protein, is an essential and fascinating process in a cell’s life as most biological activities are performed by proteins. The 18S, 5.8S, and 25S (in plants) or 28S (in mammals) rRNA genes are clustered together, forming the 45S transcription unit in plants, the 47S unit in mammals, or the 35S unit in yeast [3] Transcription of this unit to pre-rRNA is performed by RNA polymerase I (Pol I) in all eukaryotes (reviewed in [4]). RDNA loci, being repetitive sequences where transcription and replication machineries meet, are prone to recombination events that make this region one of the most unstable [6] Events such as DNA damage or a stalled replication fork are usually repaired by homologous recombination (HR), where the neighboring repeat acts as the template. We review the role of genomic instability of plant rDNA loci and mechanisms of maintaining their integrity
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