Functional genomics of gene families encoding mitochondrial proteins

[Truncated abstract] Mitochondria are organelles present in almost all eukaryotic cells. In plants it is estimated that there are 1500 to 2000 different mitochondrial proteins. The majority of these proteins are encoded by nuclear-located genes, transcribed in the nucleus, translated in the cytosol and imported into mitochondria by the combined actions of several multi-subunit protein complexes, termed translocases. In plants, many mitochondrial proteins are encoded by gene families. In some cases, these families are large, such as those encoding pentatricopeptide repeat (PPR) proteins, and the function of each protein is proposed to be involved in different processes relating to transcription and translation in mitochondria. In other cases, the gene families are small ranging from 2 to several members and it is unclear if the proteins encoded by different genes have different functions. The overall aim of the research carried out in this thesis was to carry out investigations to determine if the proteins encoded by 2 small gene families in Arabidopsis thaliana (Arabidopsis) have different functions. Two gene families were selected for study, a gene family encoding alternative or type II NAD(P)H dehydrogenases (NDs) and the gene family encoding members of the preprotein and amino acids transporters (PRAT). Seven genes encode ND type proteins in the Arabidopsis genome. Six full length cDNAs were cloned and in vitro uptake assays of radio-labelled protein into isolated mitochondria indicated that 3 genes, NDA1, NDA2 and NDC1, encoded internal or matrix facing ND proteins, while 3 genes, NDB1, NDB2 and NDB4, encoded external or intermembrane space facing ND proteins. Analysis of expression of the various ND genes, along with other components of the mitochondrial electron transport chain suggested that NDA1 was expressed in a manner that suggested it played a role in integrating mitochondrial and photosynthetic metabolism.