Identification of odorant binding proteins in Carpomya vesuviana and their binding affinity to the male-borne semiochemicals and host plant volatiles.

Carpomya vesuviana (Costa; Diptera: Tephritidae) is an agricultural pest that causes serious damage to jujube fruits. However, the mechanism of olfaction, which is critical for host identification, is not well understood in this pest. In this study, we have identified for the first time five protein types involved in the olfactory signal transduction of C. vesuviana by using transcriptome sequencing. These include 6 odorant-binding proteins (OBPs), 15 odorant receptors (ORs), 22 gustatory receptors (GRs), 2 chemosensory proteins (CSPs), and 2 sensory neuron membrane proteins (SNMPs). Amino acids alignment and phylogenetic analysis showed that all 6 OBPs have a signal peptide at their respective N-termini with four OBPs belonging with the classic OBPs, and OBP2 and OBP5 belonging to the Minus-C family. OBP3 clustered with the OBP83a/83b clade, which comprised pheromone binding protein related proteins (PBPRPs). Moreover, volatiles from C. vesuviana adults and its host plants were collected and identified by using solid phase microextraction (SPME) and gas-chromatography/mass spectrometry (GC/MS). The results indicated that male adults emitted nonanal, and five other compounds, caryophyllene, chamigrene, camphene, (Z)-3-hexen-1-ol acetate, and ocimene were identified in the fruits of jujubes. Electroantennogram (EAG) assays revealed that adult C. vesuviana responded to all six compounds along with two additional pheromones (geranyl acetate and α-farnesene) from other tephritids and the values ranged from 0.50mV to 1.26mV. To further explore the interaction between OBPs and volatiles, competitive binding assays were carried out. The results showed that only CvesOBP2 had binding affinity to (Z)-3-hexen-1-ol acetate. OBP5 and OBP6 exhibited broad spectrum binding to compounds with relatively low molecular weights, and OBP1 and OBP4 had some affinity to caryophyllene and chamigrene. However, OBP3 exhibited relatively high binding affinity to α-farnesene. The findings of this study provide insights into the olfactory mechanisms and the potential functions of OBPs in the olfactory reception pathway in C. vesuviana. The OBPs identified in this study could be used as potential targets to develop attractants to monitor this insect pest for effective pest control.