The biosynthesis of fatty acids is a primary metabolic pathway which is essential for all plant cells. In most vegetative tissues, fatty acids are used primarily for membrane synthesis and constitute 5-10% of the cell dry weight. In oil storing seeds and epidermal cells fatty acids serve additional storage and protective functions and can constitute 60% or more of the carbon flow of such cells. A molecular understanding of how cells regulate these major differences in fatty acid synthesis is not yet available and remains a central challenge for plant lipid research. Fatty acid production in the plastid appears to be tightly coupled to the utilization of acyl chains outside the plastid. Control over the pathway is likely to occur at multiple levels including short-term biochemical regulation over enzyme activities and longer-term regulation of enzyme expression levels. This project will examine control at both biochemical and expression levels with thrusts in two areas. A) Acetyl-CoA carboxylase (ACCase) is one enzyme whose activity is tightly regulated to provide control over the flux of carbon into fatty acids. Analysis of this enzyme and its role in regulation of fatty acid synthesis will be examined at the biochemical level by addressing the questions: 1) What is the role of phosphorylation in regulation of ACCase. 2) What is the nature of the multisubunit ACCase complex? In particular, are other proteins part of the complex and is membrane association important for ACCase regulation? B) Second, in some cases the supply of carbon to fatty acid synthesis in the form of acetyl-COA may regulate flux into the pathway. The predominant pathway which produces acetyl-COA in plastids has remained a major unanswered question of plant biochemistry. This question will be re-examined by detailed kinetic analysis of the in vivo flow of carbon from C02 into acetyl-CoA. The understanding to be derived from the above two thrusts should help to define the short- and long-term controls which determine how much fatty acid each plant cell produces and provide avenues toward future manipulation of this pathway in transgenic plants.
Plant oils are a major source of calories in American diets and represent an agricultural commodity worth $70 billion dollars per year worldwide. Metabolic engineering of plant pathways has the potential to transform crop plants from their traditional role of providing low-cost food and fiber toward a more profitable role of producing an array of high-value chemicals. We now have the capability to metabolically engineer the composition of plant seeds, and there has been major success in altering seed oil fatty acid composition. However in most cases, we do not yet understand which genes may be most useful to modify the quantity of seed based products or to alter carbon partitioning. This research will provide the information needed to genetically engineer plants to produce more oil and thus increase the value of agricultural products.
