An Arabidopsis homologue of bacterial RecA that complements an E. coli recA deletion is targeted to plant mitochondria

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Abstract
Homologous recombination results in the exchange and rearrangement of DNA, and thus generates genetic variation in living organisms. RecA is known to function in all bacteria as the central enzyme catalyzing strand transfer and has functional homologues in eukaryotes. Most of our knowledge of homologous recombination in eukaryotes is limited to processes in the nucleus. The mitochondrial genomes of higher plants contain repeated sequences that are known to undergo frequent rearrangements and recombination events. However, very little is known about the proteins involved or the biochemical mechanisms of DNA recombination in plant mitochondria. We provide here the first report of an Arabidopsis thaliana homologue of Escherichia coli RecA that is targeted to mitochondria. The mtrecA gene has a putative mitochondrial presequence identified from the A. thaliana genome database. This nuclear gene encodes a predicted product that shows highest sequence homology to chloroplast RecA and RecA proteins from proteobacteria. When fused to the GFP coding sequence, the predicted presequence was able to target the fusion protein to isolated mitochondria but not to chloroplasts. The mitochondrion-specific localization of the mtrecA gene product was confirmed by Western analysis using polyclonal antibodies raised against a synthetic peptide from a unique region of the mature mtRecA. The Arabidopsis mtrecA gene partially complemented a recA deletion in E. coli, enhancing survival after exposure to DNA-damaging agents. These results suggest a possible role for mtrecA in homologous recombination and/or repair in Arabidopsis mitochondria.