Silencing of odorant binding protein gene AlinOBP4 by RNAi induces declining electrophysiological responses of Adelphocoris lineolatus to six semiochemicals.

Odorant binding proteins (OBPs) are believed to be important for transporting semiochemicals through the aqueous sensillar lymph to the olfactory receptor cells within the insect antennal sensilla. Here, we injected AlinOBP4-siRNA into the conjunctivum between prothorax and mesothorax of the lucerne plant bug, Adelphocoris lineolatus and evaluated the silencing of AlinOBP4 by reverse transcription polymerase chain reaction (RT-PCR) analysis, quantitative real-time PCR (qPCR) test and electroantennogram (EAG) assay. The combination of RT-PCR and qPCR analyses revealed that the levels of messenger RNA transcript were significantly reduced ∼95% in AlinOBP4-siRNA-treated A. lineolatus males and ∼75% in RNAi-treated females within 48 hours. It was found that there are different EAG responses between male and female bugs when the AlinOBP4 gene was silenced by RNAi. The EAGs of A. lineolatus to two plant volatiles, tridecanal and hexyl alcohol, were reduced 9.09% and 79.45% in RNAi-treated males, 62.08% and 62.08% in RNAi-treated females compared to the controls, separately. Antennae of RNAi-treated bugs showed significantly lower electrophysiological responses to four sex pheromone analogs, butyl butanoate, 1-hexyl butyrate, (E)-2-hexenyl butyrate and hexyl hexanoate. The EAG recordings were reduced 35.43%, 35.24%, 39.96% and 78.47% in RNAi-treated males and 64.52%, 18.13%, 36.88% and 49.52% in RNAi-treated females, respectively. The results suggested that AlinOBP4 might play dual-roles in the identification of plant volatiles and sex pheromones. It was suspected that AlinOBP4 may have different functions in odor perception between male and female A. lineolatus.