NBS1 is involved in DNA repair and plays a synergistic role with ATM in mediating meiotic homologous recombination in plants

Abstract

SummaryThe ability of plants to repair DNA double-strand breaks (DSBs) is essential for growth and fertility. The Arabidopsis DSB repair proteins AtRAD50 and AtMRE11 form part of an evolutionarily conserved complex that, in Saccharomyces cerevisiae and mammals, includes a third component termed XRS2 and NBS1, respectively. The MRN complex (MRX in yeast) has a direct role in DSB repair and is also required for DNA damage signaling and checkpoint activation in a pathway mediated by the protein kinase ATM. This study characterizes Arabidopsis and maize NBS1 orthologues that share conserved protein motifs with human NBS1. Both plant NBS1 proteins interact with the corresponding MRE11 orthologues, and deletion analysis of AtNBS1 defines a region towards the C-terminus (amino acids 465-500) that is required for interaction with AtMRE11. Arabidopsis lines homozygous for a T-DNA insertional mutation in AtNBS1 display hypersensitivity to the DNA cross-linking reagent mitomycin C, and this phenotype can be rescued by complementation with the wild-type gene, consistent with a function for AtNBS1 in plant DSB repair. Analysis of atnbs1-1 atatm double mutants revealed a role for AtNBS1 in meiotic recombination. While atatm mutants produce reduced seed numbers, plants deficient in both AtATM and AtNBS1 are completely infertile. Cytological analysis of these double mutants revealed incomplete chromosome pairing and synapsis in meiotic prophase, and extensive chromosome fragmentation in metaphase I and subsequent stages. These results suggest a novel role for AtNBS1 that is independent of AtATM-mediated signaling and functions in the very early stages of meiosis.

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

“…The atmre11 mutants are hypersensitive to MMS and x-ray (Bundock and Hooykaas, 2002). The atatm mutants are hypersensitive to MMS and g-radiation but not to UV-B irradiation (Garcia et al, 2003), whereas atnbs1 mutants have defects in their responses to MMC and MMS but not UV-C and x-rays (Waterworth et al, 2007). The different responses of these mutants indicate that these genes play essential roles in certain DNA repair pathways; moreover, different DNA repair pathways may share some common components, implying that a highly complex network is involved in DNA repair.…”

“…UV irradiation induces DNA lesions such as cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidinone dimers (6-4 photoproducts) that can be removed by photoreactivation and NER, BER, mismatch repair, and other DNA repair pathways (Tuteja et al, 2001;Kimura et al, 2004). In Arabidopsis, most of the genes involved in the control of meiotic chromosome dynamics are also required for DNA damage repair in somatic cells (Garcia et al, 2003;Waterworth et al, 2007), but their response spectrums are quite different. The atmre11 mutants are hypersensitive to MMS and x-ray (Bundock and Hooykaas, 2002).…”

“…The osrpa1a Mutants Are Hypersensitive to DNA Mutagens Many mutants of genes related to DNA metabolism are hypersensitive to DNA mutagens such as mitomycin C (MMC), methyl methanesulfonate (MMS), and UV irradiation (Garcia et al, 2003;Bleuyard and White, 2004;Bleuyard et al, 2005;Waterworth et al, 2007). In yeast and human, RPA is involved extensively in various DNA repair pathways (Wold, 1997;Iftode et al, 1999).…”

Recognition and Repair Pathways of Damaged DNA in Higher Plants

“…Several alternative pathways may exist that allow HR based repair of DSBs, however, good evidence is provided for at least two alternative pathways in plants. One is the synthesis-dependent strand annealing (SDSA) mechanism which involves the meiotic recombination11/Rad50/X-ray sensitive 2 (MRN) complex (Waterworth et al, 2007;Ronceret et al, 2009;Amiard et al, 2010). The MRN complex is discussed to function as a first sensor of double strand breaks.…”

“…The MRN complex is discussed to function as a first sensor of double strand breaks. It generates single strand DNA at the DSB sites that can be used as templates to mediate HR by RecA and Rad51 homologues (Lin et al, 2006;Li et al, 2007;Markmann-Mulisch et al, 2007;Odahara et al, 2007;Vignard et al, 2007;Waterworth et al, 2007;Odahara et al, 2009;Ronceret et al, 2009;Amiard et al, 2010;Chittela and Sainis, 2010;Devisetty et al, 2010;Ko et al, 2010;Schaefer et al, 2010;Wang et al, 2010;Ko et al, 2011) (Fig. 4).…”