Plant mitochondria possess a short-patch base excision DNA repair pathway

Abstract

Despite constant threat of oxidative damage, sequence drift in mitochondrial and chloroplast DNA usually remains very low in plant species, indicating efficient defense and repair. Whereas the antioxidative defense in the different subcellular compartments is known, the information on DNA repair in plant organelles is still scarce. Focusing on the occurrence of uracil in the DNA, the present work demonstrates that plant mitochondria possess a base excision repair (BER) pathway. In vitro and in organello incision assays of double-stranded oligodeoxyribonucleotides showed that mitochondria isolated from plant cells contain DNA glycosylase activity specific for uracil cleavage. A major proportion of the uracil–DNA glycosylase (UDG) was associated with the membranes, in agreement with the current hypothesis that the DNA is replicated, proofread and repaired in inner membrane-bound nucleoids. Full repair, from uracil excision to thymidine insertion and religation, was obtained in organello following import of a uracil-containing DNA fragment into isolated plant mitochondria. Repair occurred through single nucleotide insertion, which points to short-patch BER. In vivo targeting and in vitro import of GFP fusions showed that the putative UDG encoded by the At3g18 630 locus might be the first enzyme of this mitochondrial pathway in Arabidopsis thaliana.

RecA-Dependent DNA Repair Results in Increased Heteroplasmy of the Arabidopsis Mitochondrial Genome

“…Repair of DSBs is essential for genome stability because they can lead to collapsed replication forks, gene loss, and cell death (Pâques and Haber, 1999). Little is known about mtDNA repair pathways in plants, although a short-patch base excision repair pathway and a microhomology-mediated BIR pathway have been shown to exist (Boesch et al, 2009;Cappadocia et al, 2010). The latter is an errorprone pathway of postreplicative DSB repair that can account for the complex rearrangements often observed in plant mitochondrial genomes (Woloszynska, 2010).…”

“…In plant mitochondria, the present knowledge about mtDNA repair is still scarce. A short-patch base excision repair pathway and a microhomology-mediated recombination pathway have been shown (Boesch et al, 2009;Cappadocia et al, 2010). However, the important HR activities that exist in plant organelles suggest that recombination-dependent repair processes are predominant.…”

Sago Palm

“…Plant mitochondrial genomes possess a low mutation rate, little compactness, large size, and highly rearranged structure (Darracq et al 2011). Furthermore, it was reported that the mt genomes of plants have a mechanism of base excision repair pathway (Boesch et al 2009) so that the nucleotide structure is very conservative. Phylogenetic construction of the 11 sago palm accessions was relatively inclined to form many groups because the high level of mt atp6-2 gene polymorphisms.…”

DNA Delivery to Mitochondria: Sequence Specificity and Energy Enhancement

“…DNA imported into isolated plant or mammalian mitochondria is transcribed in organello when carrying an appropriate mitochondrial promoter and the resulting transcripts are processed (5,6,8). Furthermore, DNA carrying specific lesions is repaired upon uptake into plant or mammalian organelles (9,10). Finally, an import substrate composed of a marker gene flanked by sequences homologous to mtDNA regions recombines with the resident DNA in plant mitochondria, leading to the integration of the marker gene (11).…”