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Abstract
The beet armyworm, Spodoptera exigua, uses (Z,E)-9,12-tetradecadienyl acetate as the major component of its sex pheromone. Previous isotope-labeling experiments demonstrated an unusual ∆12 desaturase activity involved in the biosynthesis of this compound; however, the putative ∆12 desaturase gene has not been reported to date. In the present study, we confirmed this ∆12 desaturation pathway by in vivo labeling experiments, and characterized candidate desaturase genes in a yeast heterologous expression system. We demonstrated that a pheromone gland-specific desaturase, SexiDes5, uses palmitic acid and the subsequently chain-shortened product (Z)-9-tetradecenoic acid as substrates to produce (Z)-11-hexadecenoic and (Z,E)-9,12-tetradecadienoic acids, respectively. In addition, the homologous desaturase SlitDes5 from the congeneric Spodoptera litura had analogous functions.
Highlights
Female moths emit species-specific sex pheromone blends that attract conspecific males over long distances
A number of C14 and C16 acetates and alcohols, including saturated hexadecyl acetate (16:OAc) and hexadecanol (16:OH,) monounsaturated Z9–14:OAc, Z9–14:OH, Z11–16:OAc and Z11–16:OH, and doubly unsaturated Z9,E12–14:OAc and (Z,E)-9,12-tetradecadienol (Z9,E12–14:OH), were found in gland extracts of S. exigua based on Gas Chromatography/Mass Spectrometry (GC/MS) analysis
Deuterium-labeled D3–16:acid, D9-Z11–16:acid, D3– 14:acid, D9-Z9–14:acid and D3-E12–14:acid were topically applied to the pheromone glands of S. exigua to trace the biosynthetic pathway
Summary
Female moths emit species-specific sex pheromone blends that attract conspecific males over long distances. Fatty acid desaturases that introduce double bonds in specific positions of carbon chains are the most well studied enzymes involved in moth sex pheromone biosynthesis. In vivo labeling experiments in Plodia interpunctella, which uses Z9,E12–14:OAc as a sex pheromone component, suggested the same pathway, i.e., Δ11 desaturation of palmitic acid yielding (Z)-11hexadecenoic acid (Z11–16:acid), which is chain shortened to Z9–14:acid, with Δ12 desaturation producing Z9,E12– 14:acid (Tsfadia et al 2008) In another Spodoptera species, S. littoralis, which uses (Z,E)-9,11tetradecenoic acetate (Z9,E11–14:OAc) as the major pheromone component, a Δ11 desaturase was postulated to act on the Z9–14:acid precursor to produce the pheromone compound (Dunkelblum and Kehat 1987). This was accomplished by base methanolysis, which converted fatty acyl moieties to methyl esters (Bjostad and Roelofs 1984)
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