Identification and characterisation of regulators of nuclear genes encoding mitochondrial proteins /Sophia Ng Jinq Tyan

[Truncated abstract] Mitochondria are semi-autonomous organelles in eukaryotic cells that contain over 1000 proteins. As a result of their endosymbiotic origins, they still retain a small coding capacity of less than 50 proteins in plants. The remainder of mitochondrial proteins is encoded in the nucleus, and under appropriate signals, acting via anterograde or retrograde signalling pathways, to regulate genes encoding mitochondrial proteins. While our knowledge of the mitochondrial proteins, and the various biochemical activities carried out in mitochondria is well advanced, little is known about the molecular components regulating the expression of the nuclear genes encoding mitochondrial proteins. The studies described in this thesis use forward and reverse genetic approaches to identify and characterise components that regulate the expression of genes located in the nucleus that encode mitochondrial proteins. Using reverse genetic approaches, the role of a sequence motif, called site II (5’-TGGGC(C/T)-3’), in regulation of various genes encoding mitochondrial proteins was investigated. Mutation of the site II element in a variety of promoters regions of genes encoding mitochondrial proteins revealed that they did influence the activity of the promoter, both positively and negatively, that depended on the number and arrangement of these elements and on the time of the day/night period. Binding assays using yeast one-hybrid assays indicated that the site II elements interacts with TEOSINTE BRANCHED1, CYCLOIDEA, PROLIFERATING CELL FACTOR1 (TCP) transcription factors, that can act as positive or negative regulators of gene expression. Furthermore, it was demonstrated that the TCP transcription factors interacted with regulatory components of the circadian clock...