Expression profiles and ligand-binding properties of two odorant-binding proteins from Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Abstract

Abstract The ligand-binding function of odorant binding proteins (OBPs) that are expressed exclusively or enriched in antennae are well-studied, whilst the ligand binding properties of relatively low expressed OBPs in insect antennae are still unclear. Here, two low expressed GmolOBPs (namely GmolOBP12 and GmolOBP16) were cloned based on the antennal transcriptome of Grapholita molesta, and then their expression profiles and binding properties were investigated via real-time quantitative PCR (qRT-PCR) and fluorescence binding assays, respectively. Multiple sequence alignment and phylogenetic tree analyses displayed that both of GmolOBP12 and GmolOBP16 possessed the typical six-cysteine motifs unique to the classic OBPs subfamily and were classified as such. Although the abundance of transcripts of GmolOBP12 and GmolOBP16 were relatively low compared to that of many other OBPs in the antennal transcriptome of G. molesta, qRT-PCR results indicated that the transcript levels of GmolOBP12 and GmolOBP16 in antennae were significantly higher than those in other tissues. GmolOBP12 displayed higher expression level in male antennae than in female antennae, while the transcript level of GmolOBP16 in antennae was similar for both sexes. Both recombinant GmolOBP12 and GmolOBP16 exhibited strong binding affinities to the sex pheromone (Z)-8-dodecenyl alcohol and host-plant volatile pear ester. Besides, rGmolOBP12 showed outstanding binding affinities to (E)-2-hexenal, benzaldehyde, 1-hexanol, and (Z)-3-hexenyl acetate with Ki values of 4.21, 6.81, 4.68 and 4.68 μM, respectively. rGmolOBP16 had moderate binding abilities with hexanal, decanal, 1-hexanol, methyl myristate and benzonitrile. We speculated that GmolOBP12 may have dual functions in recognition of green leaf volatiles and sex pheromone components and GmolOBP16 may participate in the detection of host-plant volatiles in chemoreception.