Poster: Secondary metabolism

Abs # 269: Genetics and biochemistry of triterpenoid biosynthesis in Arabidopsis thaliana

Presenter:	Phillips, Dereth R., derethp@rice.edu
Authors	Phillips, Dereth R. (A)   Rasbery, Jeanne  (A)   Sun, Shining  (A)   Matsuda, Seiichi P. T. (B) (A)  Bartel, Bonnie  (A)
Affiliations:	(A): Rice University, Department of Biochemistry and Cell Biology (B): Rice University, Department of Chemistry

Although terpenoids constitute the largest group of natural plant products, the biological roles of but few of these compounds are known. We are interested in the biosynthesis and biological function of triterpenoids, terpenoids derived from 30-carbon squalene and oxidosqualene precursors. Brassinosteroids and membrane sterols are examples of compounds synthesized from triterpenoid skeletons. We are exploring the biological roles and biosynthesis of these compounds by using reverse genetics in Arabidopsis, heterologous expression of plant cDNAs in yeast, spectroscopic and chromatographic structural determination, and gene expression analyses. The genes targeted by this study putatively encode farnesyl pyrophosphate synthases (2 genes), squalene synthases (2 genes), squalene epoxidases (6 genes), oxidosqualene cyclases (13 genes), and cycloeucalenol isomerase. The seeming redundancy in this pathway may suggest that each of the enzyme homologs have different substrate or product specificities, exhibit altered catalytic abilities, or maintain distinct spatial or temporal expression patterns. We are using reverse genetics to characterize the various triterpenoid biosynthesis genes. The effects of mutations in triterpenoid biosynthetic genes on plant growth, development, and triterpenoid composition will allow us to link each putative triterpenoid biosynthetic gene with an enzyme of known catalytic activity and specific biological role(s). Our goal is to provide a comprehensive catalog of triterpenoid skeletons synthesized by Arabidopsis, to establish which compounds are produced by each gene product, and to determine the spatial and temporal expression patterns of the various biosynthetic genes. (This research is supported by the NSF 2010 program.)