Investigating mitochondrial genome recombination and the effects of its destabilization on plant growth and development

Post-endosymbiosis, following the advent of modern day mitochondria, much of the ancestral endosymbiont genome was transferred to the nucleus or lost. Subsequent to an additional endosymbiotic event and the divergence of animals and plants, the animal lineage acquired a reduced configuration and the land plant mitochondrial genome underwent multiple cycles of expansion. Land plant mitochondrial genomes are characterized by the presence of multiple repeated sequences that can undergo successful DNA exchange. This repeat-mediated recombination plays a prominent role in the mitochondrial genome organization and evolution. The primary questions addressed in this thesis involve nuclear encoded proteins that participate in the maintenance of plant mitochondrial genome stability. This work resulted in identification and characterization of the novel protein RECA3 in Arabidopsis and its relationship to MSH1 in recombination surveillance.;Disruption of nuclear factors that function in the mitochondrial recombination produces an array of unusual plant phenotypes. The msh1 recA3 double mutant was used to investigate the cellular and developmental consequences to the plant of significant mitochondrial genome instability. The double mutants display a severe growth phenotype accompanied by extensive mitochondrial genome rearrangements. The double mutant also exhibits enhanced heat tolerance. Transcriptome analysis revealed altered cellular conditions that represent a stress response being primed in the double mutant grown under normal conditions. Our analysis also indicates that mitochondrial genome rearrangement in the double mutant influences differential regulation of mitochondrial transcription. Further work is required to determine the relationship between mitochondrial transcriptional modulation and retrograde signaling from the mitochondria to the nucleus that effects priming of stress response in the double mutant.