Molecular Identification, Expression, and Functional Analysis of a General Odorant-Binding Protein 1 of Asian Citrus Psyllid

For insects, odorant-binding proteins (OBPs) play an essential role in binding and transporting semiochemicals through the sensillum lymph to olfactory receptor neurons within the antennal sensilla. In the present study, the full-length cDNA encoding a general odorant-binding protein 1 (DcitOBP1, accession number KY475564) was cloned from the antennae of Diaphorina citri using RACE-PCR, and qRT-PCR analysis revealed that the DcitOBP1 gene was expressed mainly in the antennae of D. citri. In molecular docking assay, the results showed that DcitOBP1 protein has better binding affinities to the 12 selected host-plant volatile compounds. Then, the recombinant DcitOBP1 protein was expressed in Escherichia coli. After removed His-Tag, the binding properties of purified DcitOBP1 protein to the selected host-plant volatile compounds were investigated in a fluorescence ligand-binding assay, similar, but more obviously binding properties of DcitOBP1 protein result were obtained, the dissociation constant (K-D) value of DcitOBP1/1-NPN complex was 6.440 +/- 0.521, and the DcitOBP1 protein showed high binding affinities (IC50 < 100 mu M) to six of the selected ligands, namely methyl salicylate, alpha-phellandrene, (1R)-(+)-alpha-pinene, 3-carene, beta-caryophyllene, and alpha-caryophyllene. Additionally, the behavior bioassays were also showed that D. citri had significant behavioral responses toward to alpha-caryophyllene, beta-caryophyllene, (1R)-(+)-alpha-pinene, and alpha-phellandrene. Our investigation infer that the DcitOBP1 protein might play a crucial role in host-plant volatile odorants perception in D. citri, and these results also have been supplied previous insight evidence into the physiological functions of the DcitOBP1 protein of D. citri.