The Plant-Specific ssDNA Binding Protein OSB1 Is Involved in the Stoichiometric Transmission of Mitochondrial DNA inArabidopsis 

Abstract

Plant mitochondrial genomes exist in a natural state of heteroplasmy, in which substoichiometric levels of alternative mitochondrial DNA (mtDNA) molecules coexist with the main genome. These subgenomes either replicate autonomously or are created by infrequent recombination events. We found that Arabidopsis thaliana OSB1 (for Organellar Single-stranded DNA Binding protein1) is required for correct stoichiometric mtDNA transmission. OSB1 is part of a family of plant-specific DNA binding proteins that are characterized by a novel motif that is required for single-stranded DNA binding. The OSB1 protein is targeted to mitochondria, and promoter-b-glucuronidase fusion showed that the gene is expressed in budding lateral roots, mature pollen, and the embryo sac of unfertilized ovules. OSB1 T-DNA insertion mutants accumulate mtDNA homologous recombination products and develop phenotypes of leaf variegation and distortion. The mtDNA rearrangements occur in two steps: first, homozygous mutants accumulate subgenomic levels of homologous recombination products; second, in subsequent generations, one of the recombination products becomes predominant. After the second step, the process is no longer reversible by backcrossing. Thus, OSB1 participates in controlling the stoichiometry of alternative mtDNA forms generated by recombination. This regulation could take place in gametophytic tissues to ensure the transmission of a functional mitochondrial genome.

Suppression of Repeat-Mediated Gross Mitochondrial Genome Rearrangements by RecA in the Moss Physcomitrella patens

“…Mutation of MutS homolog 1 (MSH1), which encodes a homolog of E. coli MutS targeted to mitochondria, confers an accumulation of two kinds of mitochondrial DNA: one product is generated by aberrant recombination between two 249-bp repeats; another is generated by recombination between two 335-bp repeats (Abdelnoor et al, 2003;Shedge et al, 2007). A similar accumulation of recombined mitochondrial DNA molecules has been observed in an Organellar Single-stranded DNA Binding protein 1 (OSB1) mutant of Arabidopsis (Zaegel et al, 2006). In this mutant, four pairs of repeats were reported to be involved in the recombination event: a pair of 435-bp repeats and a pair of 556-bp repeats as well as the two repeat pairs that were studied in the MSH1 mutant described above.…”

Diversity of the Arabidopsis Mitochondrial Genome Occurs via Nuclear-Controlled Recombination Activity

“…This insertion was suggested to involve a 9-bp repeat-mediated integration. The sequence in question represents a recombinationally active region (Zaegel et al 2006;Shedge et al 2007). Similarly, mitochondrial genomic environments present in Col-0 have seemingly disappeared from the Ler genome (Figure 6).…”

“…Three nuclear genes have been shown to influence recombination within the plant mitochondrial genome: MSH1 (Abdelnoor et al 2003), RECA3 (Shedge et al 2007), and OSB1 (Zaegel et al 2006). Of these, MSH1 appears to have the most profound and immediate effect on the genome and on plant phenotype (Sandhu et al 2007;Shedge et al 2007).…”

Arabidopsis tRNA Adenosine Deaminase Arginine Edits the Wobble Nucleotide of Chloroplast tRNAArg(ACG) and Is Essential for Efficient Chloroplast Translation

“…Expression of the mRNAs was tested by amplification of a cDNA fragment spanning the insertion site of the T-DNA, using primers P5 and P6. Total plant RNA and genomic DNA were extracted with TRIzol and DNAzol (Invitrogen), respectively, as described (Zaegel et al, 2006).…”