Impact of the loss of AtMSH2 on double-strand break-induced recombination between highly diverged homeologous sequences in Arabidopsis thaliana germinal tissues
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We experimented a novel reporter system to analyze intrachromosomal recombination between homeologous sequences in Arabidopsis germ cell lineages. The recombination substrates used are the BAR and PAT genes which diverge by about 13% at the nucleotide level and confer resistance to the herbicide glufosinate. DNA double-strand breaks (DSBs) were generated by the I-Sce1 endonuclease to induce recombination. Loss of AtMSH2 induces a 3-fold increase of the frequency of recombination events indicating that AtMSH2 is involved in the anti-recombination activity that prevents exchange between highly diverged sequences in Arabidopsis. Molecular analysis of recombined alleles indicates that in wild type plants the single strand annealing (SSA) pathway can process more efficiently homologous 3′ ends than 3′ ends generated by resection of non-homologous overhangs. The loss of AtMSH2 disturbs this process, leading to a modification of the distribution of the BAR/PAT junctions and therefore showing that the MSH2 function is also involved in determining the structure of the recombined alleles. In addition, conversion tracts were observed in some alleles. They are shorter in MSH2 deficient plants than in wild-type, suggesting that a short-patch mismatch repair, not controlled by MSH2, could exist in Arabidopsis.
KeywordsArabidopsisthaliana Homeologous sequences Mismatch repair MSH2 Recombination Single strand annealing
The authors thank Dr. Charles White for critical reading of the manuscript, Dr. Bernard Dujon and Dr. Pascual Perez (Biogemma) for kindly providing plasmids pBios-1K and pSCM525. This work was supported by the Centre National de la Recherche Scientifique (CNRS) and by the Université Blaise-Pascal.
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