Study On The Molecular Mechanism Of The Alarm Pheromone Encoding In Pea Aphid

Insects depend on a sensitive and highly specific olfactory system to sence thousandsof odors in the environment around them. These odor molecules enter the sensillum lymphand bind to odorant-binding proteins (OBPs), which then transport the odors to the receptorsites for further stimulation. Ligand-gated ion channel composed of Orco and OR can beactivated by odors and generate potential for signal transduction, which can elicit correspondingbehavior of the insects. Aphids are one of the most destructive agriculture and forest pests.When threatened, they can release the alarm pheromone, of which the key component is(E)-β-farnesene (EBF). The alarm pheromone not only plays an important role incontrolling aphid population, but also serves as a clue for their natural enemies to findthem. In preliminary study, avoidant behavior of Acyrthosiphon pisum adults to EBF hasbeen observed through Y-tube olfactometer bioassay. To demonstrate the mechanisminvolved in EBF perception of the aphids, we further conduct functional study byknockdown of candidate OBP genes and OR genes via RNA interference technique. Theprimary results are as follows:1. Orco gene is indispensable for the alarm pheromone perception in aphid olfactorysystem. We injected dsOrco into the abdomen of A. pisum, and investigated theexpression level of this gene after RNAi. Quantitative real-time PCR (qPCR) indicated thatthe level of mRNA expression in dsOrco-injected A. pisum was significantly decreased(>50%) compared with dsGFP-injected ones. Correspondingly, dsOrco-injected A. pisumexihibited decreased EAG responses to EBF and were also less sensitive to EBF Y-tubeolfactometer bioassay..2. Both OBP3and OBP7genes play important roles in EBF perception of the aphid.After injection of both dsOBP3and dsOBP7, electroantennogram (EAG) responses of A.pisum to EBF were reduced significantly compared to controls, while the treatedindividules responded to EBF less sensitively in Y-tube olfactometer bioassay. However,the aphids with knockdown of either gene showed no significant difference in behavior response or EAG response to EBF3. Two OR genes are possibly involved in the perception of EBF in the aphids.72hafter injected dsOR5or dsOR20, the aphids significantly decreased their responses to EBFcompared to controls according to the EAG results, and Y-tube olfactometer bioassayshowed less avoidant effect of EBF on dsOR5-or dsOR20-injected A. pisum.Our study provided reasonable explanation on the molecular mechanism of EBFencoding in the aphids, A. pisum, and contributed to design of stable EBF analogues atmolecular level for further aphid control.