Production of alarm pheromone starts at embryo stage and is modulated by rearing conditions and farnesyl diphosphate synthase genes in the bird cherry-oat aphid Rhopalosiphum padi

The major component of aphid alarm pheromone is (E)-beta-farnesene (EbetaF), but the molecular mechanisms of EbetaF synthesis are poorly understood. Here we established a biological model to study the modulation of EbetaF synthesis in the bird cherry-oat aphid Rhopalosiphum padi by using quantitative polymerase chain reaction, gas chromatography/mass spectrometry and RNA interference. Our results showed that the rearing conditions significantly affected the weight of adult and modulated EbetaF synthesis in a transgenerational manner. Specifically, the quantity of EbetaF per milligram of aphid was significantly reduced in the individually reared adult or 1st-instar nymphs derived from 1-day-old adult reared individually, but EbetaF in the nymph derived from 2-day-old adult that experienced collective conditions returned to normal. Further study revealed that the production of EbetaF started in embryo and was extended to early nymphal stage, which was modulated by farnesyl diphosphate synthase genes (RpFPPS1 and RpFPPS2) and rearing conditions. Knockdown of RpFPPS1 and RpFPPS2 confirmed the role played by FPPS in the biosynthesis of aphid alarm pheromone. Our results suggested that the production of EbetaF starts at the embryo stage and is modulated by FPPS and rearing conditions in R. padi, which sheds lights on the modulatory mechanisms of EbetaF in the aphid.