Expression and evolution of Δ9 and Δ11 desaturase genes in the moth Spodoptera littoralis

Desaturation of fatty acids is a key reaction in the biosynthesis of moth sex pheromones. The main component of Spodoptera littoralis sex pheromone blend is produced by the action of Delta(11) and Delta(9) desaturases. In this article, we report on the cloning of four desaturase-like genes in this species: one from the fat body (Sls-FL1) and three (Sls-FL2, Sls-FL3 and Sls-FL4) from the pheromone gland. By means of a computational/phylogenetic method, as well as functional assays, the desaturase gene products have been characterized. The fat body gene expressed a Delta(9) desaturase that produced (Z)-9-hexadecenoic and (Z)-9-octadecenoic acids in a (1:4.5) ratio, whereas the pheromone gland Sls-FL2 expressed a Delta(9) desaturase that produced (Z)-9-hexadecenoic and (Z)-9-octadecenoic acids in a (1.5:1) ratio. Although both Delta(9) desaturases produced (Z)-9-tetradecenoic acid from myristic acid, transformed yeast grown in the presence of a mixture of myristic and (E)-11-tetradecenoic acids produced (Z,E)-9,11-tetradecadienoic acid, but not (Z)-9-tetradecenoic acid. The Sls-FL3 gene expressed a protein that produced a mixture of (E)-11-tetradecenoic, (Z)-11-tetradecenoic, (Z)-11-hexadecenoic and (Z)-11-octadecenoic acids in a 5:4:60:31 ratio. Despite having all the characteristics of a desaturase gene, no function could be found for Sls-FL4. (C) 2004 Elsevier Ltd. All rights reserved.