The Nbs1 gene is known to code for a protein involved in the hereditary cancer-prone disease, Nijmegen breakage syndrome. This gene is conserved in animals and fungi, but no plant homolog is known. The work reported here describes a homolog of Nbs1 isolated from higher plants. The Nbs1 proteins from both Arabidopsis thaliana and Oryza sativa are smaller in size than animal or yeast Nbs1, but both contain the conserved Nbs1 domains such as the FHA/BRCT domain, the Mre11-binding domain, and the Atm-interacting domain in orientations similar to what is seen in animal Nbs1. The OsNbs1 protein interacted not only with plant Mre11, but also with animal Mre11. In plants, OsNbs1 mRNA expression was found to be higher in the shoot apex and young flower, and AtNbs1 expression increased when plants were exposed to 100 Gy of X-rays. These results suggest that plant Nbs1 could participate in a Rad50/Mre11/Nbs1 complex, and could be essential for the regulation of DNA recombination and DNA damage responses.
"Only some of these proteins are conserved in Arabidopsis, but they do not participate in DSB formation (Edlinger and Schlögelhofer, 2011). For example, the tight dependence of Spo11 cleave on the MRX complex is not conserved in Arabidopsis (Gallego et al., 2001; Bleuyard et al., 2004; Puizina et al., 2004; Akutsu et al., 2007). Likewise, Ski8 orthologs are required for DSB formation in S. cerevisiae, S. pombe and Sordaria, but in Arabidopsis
Ski8 is dispensable for meiosis (Jolivet et al., 2006). "
[Show abstract][Hide abstract] ABSTRACT: Meiotic recombination plays a critical role in achieving accurate chromosome segregation and increasing genetic diversity. Many studies, mostly in yeast, have provided important insights into the coordination and interplay between the proteins involved in the homologous recombination pathway, especially the recombinase RAD51 and the meiosis-specific DMC1. Here we summarize the current progresses on the function of both recombinases and the CX3 complex encoded by AtRAD51 paralogs, in the plant model species Arabidopsis thaliana. Similarities and differences respect to the function of these proteins in other organisms are also indicated.
"Absence of RAD50 led to rapid shortening of telomeres and loss of telomere repeats accompanied by chromosome-end fusions, while in double mutant plants (rad50/tert) a synergistic effects of RAD50 and telomerase on the frequency of bridges have been found , demonstrating the dual role of the RAD50 protein in plants. A homolog of the third MRN constituent, NBS1, has been isolated in the higher plants, Arabidopsis thaliana and Oryza sativa. The NBS1 proteins from both plant species were shown to be smaller in size than animal NBS1, but both contained typical domains such as the FHA (forkhead-associated), BRCT (BRCA1 C Terminus) domain, the MRE11-binding domain, and the ATM-interacting domain. "
[Show abstract][Hide abstract] ABSTRACT: Background
Telomeres, as elaborate nucleo-protein complexes, ensure chromosomal stability. When impaired, the ends of linear chromosomes can be recognised by cellular repair mechanisms as double-strand DNA breaks and can be healed by non-homologous-end-joining activities to produce dicentric chromosomes. During cell divisions, particularly during anaphase, dicentrics can break, thus producing naked chromosome tips susceptible to additional unwanted chromosome fusion. Many telomere-building protein complexes are associated with telomeres to ensure their proper capping function. It has been found however, that a number of repair complexes also contribute to telomere stability.
We used Arabidopsis thaliana to study the possible functions of the DNA repair subunit, NBS1, in telomere homeostasis using knockout nbs1 mutants. The results showed that although NBS1-deficient plants were viable, lacked any sign of developmental aberration and produced fertile seeds through many generations upon self-fertilisation, plants also missing the functional telomerase (double mutants), rapidly, within three generations, displayed severe developmental defects. Cytogenetic inspection of cycling somatic cells revealed a very early onset of massive genome instability. Molecular methods used for examining the length of telomeres in double homozygous mutants detected much faster telomere shortening than in plants deficient in telomerase gene alone.
Our findings suggest that NBS1 acts in concert with telomerase and plays a profound role in plant telomere renewal.
"Therefore, we treated plants with c-irradiation that induces oxidative stress causing DNA single and doublestrand breaks as well as damaged bases. We compared the transcriptional profiles of GMI1 and of two repair genes known to be induced by c-irradiation (Garcia et al., 2003; Akutsu et al., 2007 "
[Show abstract][Hide abstract] ABSTRACT: DNA double-strand breaks (DSBs) pose one of the most severe threats to genome integrity, potentially leading to cell death. After detection of a DSB, the DNA damage and repair response is initiated and the DSB is repaired by non-homologous end joining and/or homologous recombination. Many components of these processes are still unknown in Arabidopsis thaliana. In this work, we characterized γ-irradiation and mitomycin C induced 1 (GMI1), a member of the SMC-hinge domain-containing protein family. RT-PCR analysis and promoter-GUS fusion studies showed that γ-irradiation, the radio-mimetic drug bleocin, and the DNA cross-linking agent mitomycin C strongly enhance GMI1 expression particularly in meristematic tissues. The induction of GMI1 by γ-irradiation depends on the signalling kinase Ataxia telangiectasia-mutated (ATM) but not on ATM and Rad3-related (ATR). Epistasis analysis of single and double mutants demonstrated that ATM acts upstream of GMI1 while the atr gmi1-2 double mutant was more sensitive than the respective single mutants. Comet assay revealed a reduced rate of DNA double-strand break repair in gmi1 mutants during the early recovery phase after exposure to bleocin. Moreover, the rate of homologous recombination of a reporter construct was strongly reduced in gmi1 mutant plants upon exposure to bleocin or mitomycin C. GMI1 is the first member of its protein family known to be involved in DNA repair.
The Plant Journal 04/2011; 67(3):420-33. DOI:10.1111/j.1365-313X.2011.04604.x · 5.97 Impact Factor
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