Transcriptional and post-transcriptional regulation of mitochondrial gene expression in Dictyostelium discoideum

To ensure normal function and biogenesis of mitochondria, the mitochondrial genome is subjected to transcriptional and post-transcriptional regulation. This thesis explored these aspects of mitochondrial gene expression in the model protist Dictyostelium discoideum. The research conducted provided new insight into the mitochondrial transcription machinery and identified a unique transcription factor (Tfb1m) with features of both human transcription factors, revealing a novel mechanism of mitochondrial transcription initiation in D. discoideum. Following mitochondrial transcription, the transcriptome is subjected to modifications mediated by several proteins. The prevalence of RNA-binding proteins that may mediate these processes was also investigated and PtcE was identified, a pentatricopeptide repeat (PPR) protein with novel domain architecture. This discovery in D. discoideum led to the identification of a novel subfamily of PPR proteins (the PPR-TGM subfamily) with a complex evolutionary history and functions in mitochondrial tRNA metabolism, including tRNA processing. RNA methylation appears to play an important role in mitochondrial RNA metabolism which is mediated by enzymes with bacterial origins. In addition to its role in transcription initiation, Tfb1m catalyses methylation of mitochondrial rRNA and originated from an α-proteobacterial methyltransferase. Likewise, methylation of mitochondrial tRNA is predicted to be catalysed by PtcE, which originated from a chlamydial methyltransferase. The work presented in this thesis highlights the significance of using the D. discoideum model for studying mitochondrial genetics and has contributed novel findings to further our understanding of the complexities of mitochondrial gene expression and its regulation.

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Microbiology, School of Life Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora.