Understanding gene expression and metabolic controls on fatty acid biosynthesis in plants

Plant fatty acids represent an important renewable source of highly reduced carbon chains that can be used for purposes ranging from food production to industrial feedstocks. So far, many attempts to engineer fatty acid production in plants have been based on current knowledge of the fatty acid metabolic pathway and the structural genes involved in it. However, plant tissues have proven to be not easily amenable to fatty acid engineering by overexpression of single FAS enzymes. These experiments lead to the conclusion that identification of regulatory factors limiting fatty acid production in plant tissues is crucial for manipulation of this metabolic pathway. At present, these factors have not been identified. Therefore, one major goal of this study has been to understand the signals and mechanisms that control fatty acid biosynthesis and the expression of genes for this primary metabolic pathway in plants.; The results presented in this study demonstrate that acyl carrier protein (ACP) genes in Arabidopsis are under multiple levels of controls and suggest that some signals known to activate fatty acid gene expression in non-plant organisms have been conserved in plants (e.g., transcriptional activation by growth/cell cycle) whereas others differ (e.g., transcriptional activation by feedback mechanisms). Light has an important role on expression of ACP genes, increasing ACP4 mRNA levels and promoting the association of ACP transcripts with polynbosomes. Thus, this study demonstrates that different ACP genes are regulated by specific signals depending on the tissue and its fatty acid-requirements.; In addition, this thesis has explored the production of saturated fatty acids and their partitioning between diverse cellular processes by focusing on the characterization of an Arabidopsis acyl-ACP thioesterase mutant ( fatb-ko). Analysis of this mutant has revealed the central role of FATB in the production of saturated fatty acids in all tissues. Moreover, redistribution of these molecules between different biosynthetic pathways in fatb-ko suggests that cells prioritize the synthesis of critical components for growth. In addition, slower growth and production of non-viable seeds in the mutant demonstrate an essential role of saturated fatty acids in plant growth and seed development.; Isotope labeling experiments and western blots were used to investigate fatty acid metabolism and protein expression in fatb-ko leaves. The results indicate that fatb-ko leaves increase the rate of fatty acid synthesis by 40% compared to wild type. (Abstract shortened by UMI.)...