Identification and Characterization of Odorant Binding Proteins in the Forelegs of Adelphocoris lineolatus (Goeze)

Abstract

The chemosensory system is essential for insects to detect exogenous compounds, and odorant binding proteins (OBPs) play crucial roles in odorant binding and transduction. In the alfalfa plant bug Adelphocoris lineolatus, an important pest of multiple crops, our understanding of the physiological roles of antenna-biased OBPs has increased dramatically, whereas OBPs related to gustation have remained mostly unexplored. In this study, we employed RNA sequencing and RACE PCR methods to identify putative OBPs from the adult forelegs of both sexes. Eight candidate OBPs were identified, and three OBPs (AlinOBP15, 16, and 17) were novel. Full-length sequence alignment and phylogenetic analyses suggested that these three candidate OBPs had characteristics typical of the insect OBP family. AlinOBP16 and 17 displayed six highly conserved cysteines, placing them in the classic OBP subfamily, whereas AlinOBP15 resembled AlinOBP14 and clustered with the Plus-C clade. Quantitative real-time PCR (qRT-PCR) revealed distinct and significant tissue- and sex-biased expression patterns. AlinOBP15 was highly expressed in female heads, and AlinOBP16 and 17 were strongly expressed in female antennae. In particular, AlinOBP11, the most abundant OBP gene in our foreleg transcriptome dataset, was predominately expressed in adult legs. Furthermore, four types of sensilla hairs were observed on the forelegs of adult A. lineolatus, including sensilla trichodea, setae, and two types of sensilla chaetica (Sch1 and Sch2). Anti-AlinOBP11 antiserum strongly labeled the outer sensillum lymph of Sch2, implying that it has important gustatory functions in A. lineolatus. Our current findings provide evidence that OBPs can be functionally expressed in the tarsal gustatory sensilla of hemipteran mirid species, broadening our understanding of OBP chemosensory function in insects and facilitating the discovery of new functional targets for the regulation of insect host-searching behaviors.

Identification of Leg Chemosensory Genes and Sensilla in the Apolygus lucorum

“…These chemosensory associated proteins are usually also expressed in insect legs. By transcriptome sequencing, OBPs, CSPs, SNMPs, GRs, and ORs were identified in the legs of Apis cerana cerana, Ectropis obliqua, and Adelphocoris lineolatus (Ma et al, 2016;Sun et al, 2017;Du et al, 2019).…”

Mating‐based regulation and ligand binding of an odorant‐binding protein support the inverse sexual communication of the greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae)

“…We believe that the distribution of these genes not only in the antennae but also in the legs suggests a transport function, probably for chemicals related to mate and/or host recognition. This has been reported for the Lucerne bug, Adelphocoris lineolatus , in which OBP11 showed both significant foreleg‐biased expression and localization in the sensilla chaetica of the forelegs through immunolocalization experiments (Sun et al ., ). This suggests that OBP11 has a gustatory function owing to its binding affinity to bitter compounds, such as quercetin and catechin (Sun et al ., ).…”

The whole body transcriptome of Coleophora obducta reveals important olfactory proteins

“…Notably, most OBPs are expressed in antennae, which indicating the important functions of OBPs in antennal identification processes, such as in C. kiangsu (Li, Jiang & Dong, 2018), H. assulta (Jin et al, 2015) and C. suppressalis (Xia et al, 2015). AlinOBP11 is expressed in the tarsal gustatory sensilla of Adelphocoris lineolatus (Sun et al, 2017a). Expression profiling showed that three CobdPBPs were more highly expressed in males than females and two exhibited significantly higher expression in males, indicating the sex biased expression of CobdPBPs, similar to Conopomorpha sinensis (Li et al, 2018); thus, these proteins may function in male binding of female-emitted pheromones.…”