Plant Physiol, October 2001, Vol. 127, pp. 584-593

Biosynthetic Pathway of Insect Juvenile Hormone III in Cell Suspension Cultures of the Sedge Cyperus iria¹

Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5 (J.C.B., S.S.T.); Center for Medical, Agricultural, and Veterinary Entomology, United States Department of Agriculture, Agricultural Research Service, P.O. Box 14565, 1700 Southwest 23 Drive, Gainesville, Florida 32604 (P.E.A.T.); and Department of Entomology, Russell Laboratories 740, University of Wisconsin, 1630 Linden Drive, Madison, Wisconsin 53706 (W.G.G.)

In most insect species, juvenile hormones regulate critical physiological processes such as metamorphosis and reproduction. In insects, these sesquiterpenoids are synthesized by retrocerebral endocrine organs, the corpora allata, via the classical mevalonate (MVA) pathway. One of these compounds, juvenile hormone III (JH III), has also been identified in the sedge Cyperus iria. In higher plants, biosynthesis of the sesquiterpenoid backbone may proceed through two distinct pathways: the MVA pathway or the 2C-methyl erythritol 4-phosphate pathway or through a combination of both pathways. Cell suspension cultures of C. iria were used to elucidate the biosynthetic pathway of JH III in the plant. Enzyme inhibition and labeling studies conclusively demonstrated that the biosynthesis of the sesquiterpenoid backbone of JH III proceeds via the MVA pathway. Inhibitor and precursor feeding studies also suggest that later steps of JH III biosynthesis in C. iria are similar to the insect pathway and that the final enzymatic reaction in JH III biosynthesis is catalyzed by a cytochrome P₄₅₀ monooxygenase.