Date of Award
Doctor of Philosophy
Biochemistry, Biophysics and Molecular Biology
Basil J. Nikolau
Plant cells appear to have at least two fatty acid forming systems, which occur in distinct subcellular compartments: plastids and mitochondria. Mitochondrial fatty acid synthase (mtFAS) is a Type II system that utilizes individual enzymes to catalyze the iterative reactions. Many of the mtFAS components have yet to be identified, and physiological functions of mtFAS are still poorly understood. In this dissertation, we characterized five Arabidopsis mtFAS components, namely mitochondrial beta-ketoacyl-ACP synthase (mtKAS), mitochondrial 3-hydroxyacyl-ACP dehydratase (mtHD), mitochondrial enoyl-ACP reductase (mtER), mitochondrial phosphopantetheinyl transferase (mtPPT), and mitochondrial malonyl-CoA synthetase (mtMCS). MtKAS, mtHD, and mtER catalyze 3 of the 4 reactions of the acyl chain elongation cycle; mtPPT is responsible for activating mitochondrial acyl carrier protein (mtACP) by the addition of a phosphopantetheine cofactor; and mtMCS generates malonyl-CoA, the donor of 2-carbon elongation unit for the mtFAS system. Mitochondrial octanoyl-ACP is the precursor for the synthesis of lipoic acid, which is the coenzyme of H-subunit of glycine decarboxylase complex (GDC), a key enzyme of photorespiration. Accordingly, mutations in the mtFAS system lead to a typical deficiency in photorespiration due to the depletion of the lipoylation of H-subunit of GDC. Lipid profiles in these mutants are also altered as a secondary effect of the deficiency in photorespiration. In addition, mutant analyses demonstrate that mitochondrial 3-hydroxymyristyl-ACP contributes to the biosynthesis of lipid A-like molecules, suggesting a novel synthetic destination of the mtFAS intermediates. RNA-seq transcriptomic analyses of the mutants establish a regulatory network that is associated with the mtFAS functions. Taken together, our results demonstrate that the mtFAS system has multiple functionalities and is crucial for plant metabolic homeostasis.
Guan, Xin, "Enzymatic components and physiological roles of mitochondrial fatty acid biosynthesis in plants" (2014). Graduate Theses and Dissertations. 13824.