Modulation of fatty acid elongation sustains sexually dimorphic hydrocarbons and female attractiveness inBlattella germanica(L.)

Insect cuticular hydrocarbons (CHCs) serve as important intersexual signaling chemicals and generally show variation between the sexes, but little is known about the generation of sexually dimorphic hydrocarbons (SDHCs) in insects. Here, we report the molecular mechanism and biological significance that underling the generation of SDHC in the German cockroach, Blattella germanica . Sexually mature females possess more C29 cuticular hydrocarbons (CHCs), especially the contact sex pheromone precursor 3,11-DimeC29. RNAi screen against fatty acid elongase gene family members and combined with heterologous expression revealed that both BgElo12 and BgElo24 were involved in HC production, but BgElo24 is of wide catalytic activities and is able to provides substrates for BgElo12 , and only the female-enriched BgElo12 was responsible for sustaining female-specific HC profile. Repressing BgElo12 masculinized the female CHC profile, decreased contact sex pheromone level and consequently reduced the sexual attractiveness of female cockroaches. Moreover, the asymmetric expression of BgElo12 between the sexes is modulated by sex differentiation cascade. Specifically, male-specific BgDsx represses the transcription of BgElo12 in males, while BgTra is able to remove this effect in females. Our study reveals a novel molecular mechanism responsible for the formation of SDHCs, and also provide evidences on shaping of the SDHCs by sexual selection, as females use them to generate high levels of contact sex pheromone.