Meeting Abstract
A mitochondrial genome is retained in all eukaryotes with a functional electron transport chain. However, in order for the mitochondria to meet the energy needs of eukaryotic cells, genetic products from the mitochondrial genome must interact intimately with those encoded by the nuclear genome. Because mtDNA is inherited differently (uni- vs. bi-parentally) and can evolve at a different rate than nucDNA, one hypothesis posits that nucDNA gene products (i.e., N-mt genes) coevolve with the mtDNA gene products they interact with in order to compensate for metabolic instability induced by mtDNA mutations. To evaluate this hypothesis, we examined rates of molecular evolution, protein structural characteristics, and expression levels in mtDNA- and nucDNA-encoded gene products in plants, since rates of mtDNA evolution and gene transfer to the nucleus are variable in different plant species. We tended to focus on closely related species in the genus Silene which vary drastically in their mtDNA substitution rates. dN/dS ratios of N-mt genes were elevated in Silene species with fast-evolving mtDNA, and substitutions in N-mt genes occurred most frequently at residues that contacted mitochondrial residues that had also undergone a substitution, providing support for the nuclear compensation hypothesis. However, the finding that N-mt genes recently transferred from the mito- to nuclear genomes have decreased expression provides support for an alternative, constraints-based hypothesis, which has been championed previously based on data from animals. We argue that both hypotheses likely contribute to observed patterns of mitonuclear evolution. These results have implications for recent theories of speciation and the evolution of sex that invoke nuclear compensation in mitonuclear genomic evolution.
