9728329 Mackenzie The plant mitochondrial genome is unusually variable in its size and highly complex in its organization when compared to its counterparts in yeast and animal systems. Of particular interest for this project is the observation that distinct mitochondrial DNA molecules, each containing only a portion of the genetic information, are retained in the genome at strikingly different relative copy number. What accounts for this unusual organization in plants is not well understood. It is clear that many features of the mitochondrial genome, including DNA copy number, are under nuclear gene control. This project is designed to test the hypothesis that nuclear-directed copy number control of mitochondrial DNA molecules serves as a means of suppressing mitochondrial mutations in plants. To test this hypothesis, the CHM gene in Arabidopsis thaliana has been cloned. Mutations in this gene result in the amplification of mitochondrial DNA molecules that contain mutations. Thus, characterization of this gene, its product, and its mode of action should allow a direct test of the stated hypothesis. We plan to confirm the identity of the CHM clone, to localize its gene product, and to genetically test its function.
