Fitness on the Genetic Level:
Mitonuclear and Mito-Mito Epistasis
Heather Fiumera, Associate Professor of Biology, Binghamton University
Monday, October 1
5:15-6:15 pm, LH 14
Cooperation between mitochondrial and nuclear genomes is required for the mitochondrial functions that underlie cell and organismal fitness, including energy production. In populations, the reorganization of genetic variation in offspring will produce new combinations of mitochondrial and nuclear alleles. Some combinations may produce more efficient interactions and improve fitness, while others may be detrimental to cellular and organismal health. We used a yeast model to determine how much mitochondrial and nuclear interactions influence phenotypic variation by replacing mitochondrial haplotypes in controlled nuclear genetic backgrounds. In different environments, we found that mitonuclear interactions explained between 10 and 40% of the phenotypic differences in our yeast collection. In certain environments, the original mtDNA-nuclear genome combinations found in nature provided fitness advantages, while synthetic mitonuclear combinations resulted in lowered growth rates and increased oxidative stress. Reorganization of mitochondrial genes between different populations also lowered growth rates, suggesting that mito-mito interactions also play a role in phenotypic variation. The decrease in fitness was correlated with genetic distance suggesting that incompatibilities between mtDNAs and nuclear genomes can arise as populations diverge. We found that exchanging mitochondrial genomes between closely related yeasts can result in severe fitness effects, and suggests that mitonuclear and even mito-mito-nuclear coevolution may contribute to speciation events in yeast. This work also highlights the need to consider mitonuclear interactions when pursuing genetic rescue strategies or the genetic basis of many human disorders.
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