Isolation and functional characterization of two independently-evolved fatty acid Delta 12-desaturase genes from insects

We report the first isolation and characterization of insect fatty acid Delta 12-desaturase genes, AdD12Des from house cricket (Acheta domesticus) and TcD12Des from the red flour beetle (Tribolium castaneum), responsible for the production of linoleic acid from oleic acid. Sequence analysis shows the cricket and flour beetle Delta 12-desaturase genes have evolved independently from all previously known Delta 12-desaturases and are much more closely related to the archetypal stearoyl-Coenzyme A-acting desaturase from rat than to the phospholipid-acting Delta 12-desaturases widely reported in plants. Phylogenetic and functional analysis indicates the cricket AdD12Des gene may have evolved from an ancestral Delta 9-desaturase. By contrast, the beetle Delta 12-desaturase is distantly related to the cricket genes and beetle Delta 9-desaturases suggesting evolution by an independent route. Linoleic acid has key physiological roles in insects and this is the first report of genes capable of producing this essential fatty acid in higher animals.