Semi-selective fatty acyl reductases from four Heliothine moths influence the specific pheromone composition

Background: Sex pheromones are essential in moth mate communication. Information on pheromone biosynthetic genes
and enzymes is needed to comprehend the mechanisms that contribute to specificity of pheromone signals. Most
heliothine moths use sex pheromones with (Z)–11–hexadecenal as the major component in combination with minor fatty
aldehydes and alcohols. In this study we focus on four closely related species, Heliothis virescens, Heliothis subflexa,
Helicoverpa armigera and Helicoverpa assulta, which use (Z)–11–hexadecenal, (Z)–9–tetradecanal, and (Z)–9–hexadecenal in
different ratios in their pheromone blend. The components are produced from saturated fatty acid precursors by
desaturation, b–oxidation, reduction and oxidation.
Results: We analyzed the composition of fatty acyl pheromone precursors and correlated it to the pheromone composition.
Next, we investigated whether the downstream fatty–acyl reduction step modulates the ratio of alcohol intermediates
before the final oxidation step. By isolating and functionally characterizing the Fatty Acyl Reductase (pgFAR) from each
species we found that the pgFARs were active on a broad set of C8 to C16 fatty acyl substrates including the key
pheromone precursors, Z9–14, Z9–16 and Z11–16:acyls. When presenting the three precursors in equal ratios to yeast
cultures expressing any of the four pgFARs, all reduced (Z)–9–tetradecenoate preferentially over (Z)–11–hexadecenoate, and
the latter over (Z)–9–hexadecenoate. Finally, when manipulating the precursor ratios in vitro, we found that the pgFARs
display small differences in the biochemical activity on various substrates.
Conclusions: We conclude that a pgFAR with broad specificity is involved in heliothine moth pheromone biosynthesis,
functioning as a semi–selective funnel that produces species–specific alcohol product ratios depending on the fatty–acyl
precursor ratio in the pheromone gland. This study further supports the key role of these in pheromone biosynthesis and
emphasizes the interplay between the pheromone fatty acyl precursors and the Lepidoptera specific pgFARs in shaping the
pheromone composition.