Frequency, mechanisms, and intermediates of mitochondrial gene transfer to the nucleus

Most mitochondrial genes were lost or transferred to the nucleus early in eukaryotic evolution, relatively soon after the endosymbiotic origin of the mitochondrion. Gene transfer to the nucleus is an ongoing process in flowering plants. This dissertation was intended to further our understanding of the frequency, mechanisms, and intermediate stages of the process. Comparative study of the cox2 gene transfer in legumes elucidated two novel intermediate stages of the gene transfer process and the phylogenetic timing and frequency of these stages. The frequency, rates, and patterns of mitochondrial gene losses during angiosperm evolution were comprehensively explored by surveying 281 angiosperm DNAs for the presence or absence of 30 mitochondrial genes. Numerous gene losses were discovered, and the rate of loss is very high in several widely separated lineages. To determine if the gene losses reflect transfers to the nucleus and to determine if many transfers have occurred, one gene (rps10) was studied in detail. A remarkably large number of transfers were characterized, changing our view about the frequency of the process. This study also revealed novel mechanisms by which newly transferred genes can gain mitochondrial targeting presequences and documented the first examples of recently transferred genes without presequences. Frequent gene transfers to the nucleus also characterize the evolution of two succinate dehydrogenase genes in angiosperms. One succinate dehydrogenase gene (sdh3) was documented for the first time in angiosperm mitochondria and two transfers of this gene to the nucleus provide further perspectives on the origin of mitochondrial targeting presequences. An unusual case of mitochondrial gene fission and transfers to the nucleus has been characterized, suggesting that part of a gene was transferred to the nucleus prior to gene fission in the mitochondrial genome. This dissertation research has furthered our knowledge of the frequency of gene transfers to the nucleus and losses from the mitochondrion, the intermediate stages of the process, and mechanisms for the acquisition of mitochondrial targeting function by newly transferred genes.