title: Homology-dependent repair is involved in 45S rDNA loss in plant CAF-1 mutants.
abstract: 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.
authors.affiliation: Mendel Centre for Plant Genomics and Proteomics, CEITEC, Masaryk University, Kamenice 5, CZ-62500, Brno, Czech Republic; Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlářská 2, CZ-61137, Brno, Czech Republic.
authors.forename: Veronika
authors.initials: V
authors.lastname: Muchová
authors.forename: Simon
authors.initials: S
authors.lastname: Amiard
authors.forename: Iva
authors.initials: I
authors.lastname: Mozgová
authors.forename: Martina
authors.initials: M
authors.lastname: Dvořáčková
authors.forename: Maria E
authors.initials: ME
authors.lastname: Gallego
authors.forename: Charles
authors.initials: C
authors.lastname: White
authors.forename: Jiří
authors.initials: J
authors.lastname: Fajkus
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D056504:Chromatin Assembly Factor-1 / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000235:genetics / Q000502:physiology; D004275:DNA, Ribosomal / Q000235:genetics*; D042822:Genomic Instability / Q000235:genetics / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D056504:Chromatin Assembly Factor-1; D004275:DNA, Ribosomal; C422044:FAS protein, Arabidopsis; C503692:RAD51B protein, Arabidopsis
keywords: 45S rDNA; Arabidopsis thaliana; DNA repair; FAS1; FAS2; RAD51B; chromatin assembly factor 1; genome instability