An odorant-binding protein of Asian citrus psyllid, Diaphorina citri, participates in the response of host plant volatiles

BACKGROUND Odorant-binding proteins (OBPs) in insects contribute to the sensitivity of the olfactory system and connect external odorants to olfactory receptor neurons. Determination of the chemosensory functions in Diaphorina citri, a vector of the citrus Huanglongbing pathogen, may help in developing a potential target for pest management. RESULTS Diaphorina citri showed dose-dependent electroantennogram recording (EAG) responses to 12 host plant volatiles. A two-choice behavioral trap experiment showed that four compounds (methyl salicylate, linalool, citral and R-(+)-limonene) that elicited high EAG responses also had significant attraction to adults. The expression profiles induced by these compounds were detected in nine OBP genes, DcitOBP1-9. DcitOBP3, DcitOBP6 and DcitOBP7 commonly showed significant upregulation or downregulation compared with the control. Microscale thermophoresis (MST) showed that the recombinant protein DcitOBP7 had high in vitro binding affinities (K-d < 10 mu m) to methyl salicylate, linalool and R-(+)-limonene, and moderate binding affinity to citral with a K-d value of 15.95 mu m. Furthermore, RNA interference (RNAi)-suppressed messenger RNA (mRNA) expression of DcitOBP7 resulted in a significant reduction in EAG activity and in adult D. citri behavioral responses to tested volatiles and the preferred host, Murraya paniculata. The hydrophilic residue Arg107 of DcitOBP7 may have a key role in binding odorants via formation of hydrogen bonds. CONCLUSION These results show that DcitOBP7 plays an important role in the olfactory response. This finding may provide new insight into the functions of OBP families in D. citri and aid in the development of safe strategies for managing D. citri populations.

Automated summary

Diaphorina citri showed dose-dependent EAG responses to 12 host plant volatiles, with four compounds eliciting significant attraction to adults; expression profiles of nine OBP genes showed significant upregulation or downregulation; recombinant protein DcitOBP7 exhibited high in vitro binding affinities to certain odorants and RNAi-suppression of DcitOBP7 resulted in reduced EAG activity and behavioral responses in D. citri.