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

Abstract

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 P 450 monooxygenase.Juvenile hormones are a group of structurally related sesquiterpenoids that regulate critical physiological processes including metamorphosis and reproduction in most insect species (Gilbert et al., 1996). Juvenile hormone III (JH III), methyl-10R,11-epoxy-3,7,11-trimethyl-2E,6E-dodecadienoate, has also been identified in the sedge Cyperus iria (Toong et al., 1988).The presence of an insect hormone and its high levels in C. iria throughout development suggest that this compound may play a role in protection of the plant against insect herbivory (Toong et al., 1988; Bede et al., 1999a). However, there is no evidence that JH III functions as a feeding deterrent. Therefore, any antiherbivory activity would arise from its ability to interfere with insect development. In two laboratory studies, contact of insects with C. iria effectively disrupted development (Toong et al., 1988;Schwartz et al., 1998). These effects were attributed to the JH III content of the plant. However, conclusive evidence that this hormone protects C. iria against insect herbivory has not yet been demonstrated. We have proposed alternatively that JH III may function as an allelopathic agent in C. iria (Bede and Tobe, 2000). This plant species is an extremely invasive weed, responsible for economic losses in many important crops such as rice (Oryza sativa; Holm et al., 1977; Catling, 1992). Treatment of seeds with JH III delays lettuce (Lactuca sativa) seed germination and inhibits shoot growth of rice seedlings (Bede and Tobe, 2000). Therefore, it is possible that this compound confers an ecological advantage to C. iria by leaching from the roots, in which the highest levels are localized, into the immediate environment and affecting the germination and growth of neighboring competing plant species.Temporal and spatial changes in JH III levels are observed in C. iria throughout development (Bede et al., 1999a). JH III levels increased in the immature se...

Carotenoid Biosynthesis in the Primitive Red Alga Cyanidioschyzon merolae

“…Cultures of C. merolae were grown in the presence of three general inhibitors of P450 enzymes. Two of the inhibitors tested, clotrimazole and miconazole, at the relatively high concentrations used in these experiments (the concentrations used in this study were the same as used by Bede et al [4] for cell suspension cultures of the sedge Cyperus iria, except that ancymidol was used in the present study at a 3.3-fold-higher concentration), very quickly (within one day) killed and bleached cultures of C. merolae. In the presence of the third inhibitor tested, ancymidol, cultures of C. merolae continued to grow and divide at the same rate as control cultures (as measured by the optical density at 730 nm) for about two generations before a relatively sudden arrest of growth.…”

Insecticidal and Anti-juvenile Hormone Activities of Precocene II against the Grasshopper Euprepocnemis plorans plorans Charp. Orthoptera: Acrididae.

“…It should be mentioned that the use of juvenile hormone (JH) or JH-based compounds for pest control was early suggested by some authors [15][16][17] as "third generation insecticides". Screening new targets involved in JH-biosynthesis within the corpora allata (CA), JH-producing organs in insects, has been a subject of study in the past four decades [18]. So, compounds that interact with JH, stimulate JHbiosynthesis, inhibit JH-biosynthesis or interfere with its catabolism can be utilized as new insecticides against insect pests [19].…”

Lepidopteran HMG-CoA reductase is a potential selective target for pest control

“…It has been demonstrated that the design of JH mimics or anti-JH agents is an effective strategy for insecticide discovery. Screening new targets involved in JH biosynthesis has been a subject of study for two decades (Bede et al, 2001). As HMGR has been postulated to be a key enzyme in the regulation of the MVA pathway in insects, some HMGR inhibitors (statins) have been used to investigate their effects on JH biosynthesis.…”