Poster: Lipids & Related Molecules

Abs # 860: ATP-citrate lyase generates cytosolic acetyl-CoA

Presenter:	Fatland, Beth L., bfatland@iastate.edu
Authors	Fatland, Beth L. (A)   Perera, Ann  (B)   Nikolau, Basil J. (B)   Wurtele, Eve S. (A)
Affiliations:	(A): Iowa State University, Department of Botany (B): Iowa State University, Department of Biochemistry, Biophysics and Molecular Biology

Acetyl-CoA is an intermediate of both primary and secondary metabolism. Acetyl-CoA-requiring metabolism occurs in a number of subcellular compartments. Because acetyl-CoA cannot readily cross membranes, compartmentalized biosynthesis is required. Cytosolic acetyl-CoA can undergo carboxylation or condensation, which generates malonyl-CoA or acetoacetyl-CoA, respectively. Products from the carboxylation pathway contribute to the elongation of fatty acids and the biosynthesis of a variety of other phytochemicals, including flavonoids and malonic acid. The condensation pathway leads into the biosynthesis of HMG-CoA-derived isoprenoids, including sterols and brassinosteroids. ATP-citrate lyase (ACL) catalyzes the ATP-dependent reaction between citrate and CoA to form oxaloacetate and acetyl-CoA. We have shown that ACL is located in the cytosol, and is not detectable in the plastids, mitochondria, or peroxisomes. To further test the hypothesis that ACL is a source of cytosolic acetyl-CoA we have generated transgenic Arabidopsis plants that have reduced ACL activity due to the expression of an antisense ACL RNA. These plants show a complex, miniaturized phenotype, with smaller cells, aberrant plastid morphology, hyperaccumulation of anthocyanin and starch and reduced accumulation of cuticular waxes. Supplementation with malonate and select sterols alleviates these characteristic antisense phenotypes, while epibrassinolide or campesterol do not. Phenotypic similarity to wild type plants treated with mevinolin (an HMG-CoA reductase inhibitor) and mutants with altered sterol metabolism leads to the hypothesis that plants with reduced ACL may have reduced sterol accumulation. To address this hypothesis, metabolite profiling is being conducted and will be discussed.