Sex pheromone biosynthesis in the Oriental fruit moth Grapholita molesta involves Δ8 desaturation

The Oriental fruit moth Grapholita molesta is distributed throughout temperate regions and considered to be a pest in peach production and other high-value fruit crops in the rose family. Insecticide treatment has led to resistance development, but the use of sex pheromones in pest management has shown great promise. We investigated the pheromone biosynthesis pathway in G. molesta with the aim of elucidating pheromone evolution in the Olethreutinae subfamily of moths and harnessing pathway genes in biotechnological production of sex pheromone for use in pest management. In vivo labelling experiments suggested that an uncommon Δ8 fatty acyl desaturase is involved in sex pheromone biosynthesis. CRISPR/Cas9 knock-out of the highly expressed candidate desaturase gene Gmol_CPRQ almost completely blocked the production of Δ8 pheromone components in vivo. Heterologous expression of Gmol_CPRQ protein in yeast- or Sf9 insect cells, however, failed to demonstrate the expected Δ8 desaturase activity. Instead, Δ9 desaturase activity was observed. Co-expression in the yeast system of the electron donor, cytochrome b5, from G. molesta still produced only Δ9 desaturase activity. We suggest that Gmol_CPRQ is intimately involved in pheromone production in vivo, via an unknown reaction mechanism that may possibly involve another co-factor that is absent in the yeast and Sf9 expression systems, or depend on its subcellular site of activity. Solving this puzzle will shed further light on pheromone biosynthesis in the family Tortricidae and will be required for successful biotechnological production of fatty acids and pheromones requiring Δ8 desaturation.