A RecG-like DNA helicase is involved in the surveillance of recombination and segregation of plant organellar genomes

A RecG-like DNA helicase is involved in the surveillance of recombination and segregation of plant organellar genomes Clémentine Wallet, Monique Le Ret, André Dietrich and José Gualberto The plasticity of plant mitochondrial genomes is due to recombination processes that modulate their structure. Several factors have already been identified involved in organellar recombination or in recombination-dependent repair processes. But how the segregation of the alternative mitotypes generated by recombination is controlled, is still not understood. An Arabidopsis gene (RECG1) codes for a homologue of bacterial DNA helicase RecG. In bacteria RecG has multiple roles in DNA repair, the control of stoichiometric genome replication and the suppression of ectopic recombination. The plant RECG1 is dually targeted to mitochondria and plastids and can complement bacterial recG deficient strains for repair and replication control. Arabidopsis recG1 mutants have increased ectopic recombination between intermediate size repeat (IR) in mitochondria, and are deficient in repair of double strand breaks induced by a genotoxic stress. In addition we found that RECG1 has roles in the segregation of mtDNA. In a recG1 line an alternative mtDNA sequence generated by recombination is stably maintained as an independent replisome. Reintegration of the wild type RECG1 allele leads to the segregation of the alternative versions of mtDNA, with individual plants inheriting different mtDNA versions. The precise characterization of the recombination steps involved in this sorting process allowed us to build a model for how it is controlled by RECG1.