Identification of Host-Plant Volatiles and Characterization of Two Novel General Odorant-Binding Proteins from the Legume Pod Borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae)

Abstract

Chemoreception is a key feature in selection of host plant by phytophagous insects, and odorant-binding proteins (OBPs) are involved in chemical communication of both insects and vertebrates. The legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae) is one of the key pest species of cowpea and widely distributed throughout tropical and subtropical regions, causing up to 80% of yield loss. In this study, we investigated the electrophysiological responses of female M. vitrata to floral volatiles from V. unguiculata. Seventeen electroantennogram-active compounds were identified from floral volatiles of V. unguiculata by coupled gas chromatography-electroantennography (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Then, we cloned two novel full-length GOBP genes (MvitGOBP1 and MvitGOBP2) from the antennae of M. vitrata using reverse transcription PCR. Protein sequence analysis indicated that they shared high sequence similarity with other Pyralididae insect GOBPs and had the typical six-cysteine signature. Real-time PCR analysis indicated that MvitGOBP1-2 mRNA was highly expressed in the antennae of female adult with several thousands-fold difference compare to other tissue. Next, the recombinant MvitGOBP1-2 was expressed in Escherichia coli and purified using Ni ion affinity chromatography. Fluorescence binding assays demonstrated that MvitGOBP1-2 had different binding affinities with 17 volatile odorant molecules including butanoic acid butyl ester, limonene, 4-ethylpropiophenone, 1H-indol-4-ol, butanoic acid octyl ester and 2-methyl-3-phenylpropanal. In the field trapping experiment, these six floral volatiles could effectively attract female moths and showed significant difference compared with the blank lure. These results suggested that MvitGOBPs and the seventeen floral volatiles are likely to function in the olfactory behavior response of female moths, which may have played crucial roles in the selection of oviposition sites. The six compounds that we have identified from the volatiles of V. unguiculata may provide useful information for exploring efficiency monitoring and integrated pest management strategies of this legume pod borer in the field.

Identification of odorant‐binding and chemosensory protein genes and the ligand affinity of two of the encoded proteins suggest a complex olfactory perception system in Periplaneta americana

“…This finding suggests that OBP1 and OBP2 can detect not only sex pheromone components but also other odorants from food or plant sources, such as farnesene, farnesol, 2‐tridecanone and tetradecane, which presented higher affinities [displacement constant (Ki) <2 μM] in our earlier study (Li et al ., ). PameOBP4 , 24 , 38 and 49 were expressed equally in the antennae of both sexes, indicating that they play roles in perceiving general host volatiles, similar to the GOBPs of moths (Zhou et al ., ; Li et al ., ). For the CSPs, 10 of the 14 (71.42%) genes were expressed dominantly in the chemosensory organs (Fig.…”

“…Therefore, we focused on one OBP ( PameOBP24 ) and one CSP ( PameCSP7 ) that were equally expressed in the antennae of both sexes and that were relatively highly expressed amongst the OBPs and CSPs based on our transcriptome data (RPKM values), which indicated that they may facilitate the detection of plant and/or food source odorants in both sexes and play key roles in the olfactory function of both sexes. The functions of the selected OBP and CSP may be like those in some of moth GOBPs, which participate in detecting common plant odorants (Liu et al ., ; Zhou et al ., ) and may be crucial for P. americana to locate different hosts. The two selected genes, PameOBP24 and PameCSP7 , were used to express recombinant proteins to further investigate their odorant affinities in vitro .…”

Identification and expression profiles of novel odorant binding proteins and functional analysis of OBP99a in Bactrocera dorsalis

“…Previous studies have reported many OBPs that are expressed in the larval stages and adult stage (Xue et al., ; Zhou et al., ). In Sclerodermus sp., OBP3 is highly expressed in the larvae, which suggests that this protein has a basic and conserved role, perhaps in feeding or identifying general volatiles (Zhou et al., ).…”

“…Previous studies have reported many OBPs that are expressed in the larval stages and adult stage (Xue et al., ; Zhou et al., ). In Sclerodermus sp., OBP3 is highly expressed in the larvae, which suggests that this protein has a basic and conserved role, perhaps in feeding or identifying general volatiles (Zhou et al., ). Our results reveal that OBP19c, OBP44a, OBP99a , and OBP99d are expressed from the prepupa to the adult stage, which suggests their putative roles in the discrimination of mating partners and egg‐laying substrates (Zhou et al., ).…”

“…In Sclerodermus sp., OBP3 is highly expressed in the larvae, which suggests that this protein has a basic and conserved role, perhaps in feeding or identifying general volatiles (Zhou et al., ). Our results reveal that OBP19c, OBP44a, OBP99a , and OBP99d are expressed from the prepupa to the adult stage, which suggests their putative roles in the discrimination of mating partners and egg‐laying substrates (Zhou et al., ). OBP44a was found to be abundantly expressed in the pupal stage, which agrees with another study of Anopheles stephensi that reported that AsteObp1 levels peaked in the late pupae stage, which suggests a possible chemosensory role for this gene in pupae, or perhaps a simple correlation with the onset of development of chemosensory tissue during pupation (Sengul & Tu, ).…”