Mre11 Deficiency in Arabidopsis Is Associated with Chromosomal Instability in Somatic Cells and Spo11-Dependent Genome Fragmentation during Meiosis

Abstract

The Mre11/Rad50/Nbs1 complex is involved in many aspects of chromosome metabolism. Aberrant function of the complex is associated with defects in the DNA checkpoint, double-strand break repair, meiosis, and telomere maintenance. In this article, we report the consequences of Mre11 dysfunction for the stability of mitotic and meiotic chromosomes in Arabidopsis thaliana. Although plants homozygous for a T-DNA insertion in a conserved region of the MRE11 gene are viable, they exhibit growth defects and are infertile. Analysis of mitotic chromosomes prepared from the mutant plants revealed abundant dicentric chromosomes and chromosomal fragments. Fluorescence in situ hybridization showed that anaphase bridges are often formed by homologous chromosome arms. The frequency of chromosome fusions was not reduced in mre11 ku70 double mutants, suggesting that plants possess DNA end-joining activities independent of the Ku70/80 and Mre11 complexes. Cytogenetic examination of pollen mother cells revealed massive chromosome fragmentation and the absence of synapsis in the initial stages of meiosis. The fragmentation was substantially suppressed in mre11 spo11-1 double mutants, indicating that Mre11 is required for repair but not for the induction of Spo11-dependent meiotic DNA breaks in Arabidopsis

Double-stranded DNA breaks and gene functions in recombination and meiosis

“…Abnormalities in mitotic development is not obvious under normal growth conditions; however, mutant plants exhibit an increased sensitivity to the DNA-damaging agent methylmethane sulfonate [57]. An Arabidopsis atmre11 mutant meiocytes lack chromosome synapsis, and both mitotic and meiotic mutant cells contain AtSPO11-1-dependent chromosome fragments, suggesting that this gene functions downstream of AtSPO11-1; this is consistent with the function of RAD50-MRE11-XRS2 complex in budding yeast [35]. Moreover, the meiotic breaks in atmre11 are not completely suppressed by atspo11-1 mutation, indicating that other pathways might be involved in generating DSBs.…”

“…Non-crossover Crossover npg eliminated in a spo11 background in different organisms, suggesting that SPO11 is responsible for generating DSBs during meiosis [29][30][31][32][33][34][35]. Furthermore, mutant studies have been performed with some of the identified SPO11 genes.…”

Replication Protein A (RPA1a) Is Required for Meiotic and Somatic DNA Repair But Is Dispensable for DNA Replication and Homologous Recombination in Rice

“…Among these mutants, atrad50, atmre11, atrad51, atrad51c, and atxrcc3, which have defects in the repairing of AtSPO11-induced DSB, exhibited similar meiotic chromosome behaviors like asynaptic homologs and/or chromosome fragmentation (Bleuyard et al, 2004a;Bleuyard and White, 2004;Li et al, 2004Li et al, , 2005Puizina et al, 2004). The meiotic chromosome fragmentation could be suppressed by mutation in AtSPO11-1 (Bleuyard et al, 2004b;Li et al, 2004Li et al, , 2005Puizina et al, 2004), which provides a direct evidence that the origin of the DNA breaks in these mutants is the unrepaired DSBs generated by AtSPO11. However, the atspo11-1 mutation only partially rescues meiotic chromosome fragmentation in atspo11-1/atatr, atspo11-1/ atatm double mutants and the atspo11-1/atatr/atatm triple mutant (Culligan and Britt, 2008).…”

“…Mutation in Arabidopsis MRE11, a gene involved in meiotic DNA repair, results in mitotic chromosomal fragmentation at anaphase (Puizina et al, 2004). RT-PCR assays and the expression pattern obtained from chip databases revealed that OsRPA1a was expressed universally, with rather high expression in proliferating tissues such as callus and shoot apical meristem (http://crep.ncpgr.cn/; http://signal.salk.edu/cgi-bin/RiceGE?JOB=EXPR& TYPE).…”

The multiple roles of the Mre11 complex for meiotic recombination

“…In particular, all organisms tested show defects in meiotic recombination in Mre11 complex mutants, e.g. in C. elegans (Chin & Villeneuve 2001), in Coprinus cinereus (Ramesh & Zolan 1995, Gerecke & Zolan 2000, Merino et al 2000, in Arabidopsis thaliana (Gallego et al 2001, Bundock & Hooykaas 2002, Puizina et al 2004, in Aspergillus nidulans (Semighini et al 2003, Malavazi et al 2005 or in Schizzosaccharomyces pombe (Young et al 2004).…”