Three chemosensory proteins from the sweet potato weevil, Cylas formicarius, are involved in the perception of host plant volatiles.

BACKGROUND: Chemosensory proteins (CSPs) play important roles in chemical communication, but their precise physiological functions are still unclear. Cylas formicarius is the most serious pest attacking sweet potato around the world. At present, there is no effective way to control this pest. RESULTS: Our results showed that CforCSP1, 5 and 6 genes were highly expressed in the antennae of both sexes of C. formicarius. In addition, results from a fluorescence competitive binding assay showed that the CforCSP1, 5 and 6 proteins had high binding affinities for 17 plant volatiles including eight host plant volatiles. This indicated that the three proteins may be involved in the detection of host plant volatiles. Furthermore, results from four-arm olfactometer bioassays showed that there was a significant tendency for C. formicarius to be attracted to eucalyptol, ß-carotene, benzaldehyde, vanillin and phenethyl alcohol, while it was repelled by ß-ionone. Finally, the levels of expression of the three CforCSPs in C. formicarius were successfully inhibited by RNA interference (RNAi). Behavioral experiments showed that CforCSP1, 5 and 6-deficient C. formicarius were partly anosmic to ß-cyclocitral, benzaldehyde, octyl aldehyde, and ß-ionone and exhibited a reduced ability to locate the host plant volatiles ß-carotene and vanillin. CONCLUSION: Our data suggest that CforCSP1, 5 and 6 likely are involved in the chemical communication between C. formicarius and host plant volatiles, which may play pivotal roles in oviposition and feeding site preferences. More importantly, these results could provide information for the development of monitoring and push-pull strategies for the control of C. formicarius. © 2021 Society of Chemical Industry.

Functional characteristic analysis of three odorant-binding proteins from the sweet potato weevil (Cylas formicarius) in the perception of sex pheromones and host plant volatiles.

BACKGROUND: The sweet potato weevil, Cylas formicarius, is the most serious pest of sweet potato worldwide. The molecular mechanism of sex pheromone recognition in C. formicarius has not been reported. Odorant-binding proteins (OBPs) play a critical role in selectively binding and transporting pheromones or other odors to the surface of olfactory receptor neurons through the aqueous sensillar lymph, therefore the function of sweet potato OBPs is worth studying. RESULTS: Herein, the CforOBP1-3 genes encoding three classical OBPs were cloned in C. formicarius by reverse transcription-polymerase chain reaction. Phylogenetic analysis showed that CforOBP1-3 were homologous genes, but the relationship between CforOBP2 and CforOBP3 was closest among the three genes. In addition, real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays demonstrated that the expression of CforOBP1 was higher in the antennae and legs of female and male insects, while CforOBP2 and CforOBP3 were mainly expressed in the antennae of male insects. The fluorescent competitive binding assay results indicated that CforOBP1-3 had strong binding affinities to sex pheromones and other tested ligands. Finally, the mRNA expression of CforOBP1-3 was successfully inhibited by RNA interference, and in vivo behavioral experiments showed that CforOBP1-3-deficient C. formicarius was partly anosmic and lost some of its ability to locate sex pheromones and host plant volatiles. CONCLUSION: These results suggested that CforOBP1 was shown to be involved in the process of weevils feeding and finding sweet potato, and CforOBP2-3 were mainly involved in the mating behavior of adult male weevils.

Functional characterizations of one odorant binding protein and three chemosensory proteins from Apolygus lucorum (Meyer-Dur) (Hemiptera: Miridae) legs.

Chemoreception plays an important role in insects for sensing information when searching for host and oviposition sites. An understanding of the chemosensory mechanism could aid in the development of new methods to effectively prevent damage from insects in agriculture. We have constructed a legs cDNA library for Apolygus lucorum and sequenced 1584 ESTs, from which we identified 669 unigenes. From this collection we identified one putative odorant binding protein (AlucOBP5) and three chemosensory proteins (AlucCSP2, AlucCSP3, AlucCSP4) genes. Using real-time PCR method, we assessed the expression of these genes in the head, thorax, abdomen, wing, antenna and mouthparts. Results indicate that the expression of these genes had tissue- and gender-specificity. AlucCSP2 and AlucCSP3 were specifically expressed in female wings. AlucCSP4 was expressed relatively highly in female wings but also expressed in other tissues. AlucOBP5 was expressed in female abdomen and male legs with high levels in the latter. Expression vectors for these proteins were constructed and expressed in BL21(DE3). The purified proteins were then tested for binding properties using bis-ANS as the fluorescent ligand. AlucOBP5 could bind strongly with phenyl acetaldehyde, 1-hexanol, 3-hexenal and ß-ionone. AlucCSP2 and AlucCSP3 had low affinity with all general odorants. AlucCSP4 did not bind with any of the standards. All four proteins could bind with gossypol, meletin with high affinity and could also bind with rutin hydrate, although AlucCSP4 had weak binding capacity. AlucCSP3 and AlucCSP4 could bind weakly with catechin, while AlucCSP2 and AlucOBP5 could not.

Identification and binding characterization of three odorant binding proteins and one chemosensory protein from Apolygus lucorum (Meyer-Dur).

For the sucking insect, Apolygus lucorum, taste is essential for finding host plants and oviposition sites. In A. lucorum, taste relies largely on the sensory system located within its proboscis. In this study, we constructed a cDNA library from A. lucorum proboscises and conducted preliminary analysis of 1554 ESTs. From this collection, we identified three putative odorant-binding proteins (AlucOBP3, AlucOBP4, AlucOBP6) and one chemosensory protein (AlucCSP1). Quantitative real-time polymerase chain reaction (qPCR) was used to study the expression pattern of these four genes. All four were expressed mainly in antennae, proboscises and legs, suggestive of roles in olfaction and gustation. We expressed and purified recombinant versions of AlucOBP3, AlucOBP4, AlucOBP6, and AlucCSP1 in a prokaryotic expression system. The ligand-binding specificities of the four proteins then were investigated in competition assays using 4,4'-dianilino-1,1'-binaphthyl-5, 5'-sulfonic acid (bis-ANS) as a probe. Of the 58 small organic compounds and five cotton secondary metabolites tested, plant volatiles cannot effectively displace bis-ANS from any of the four proteins. In contrast, most of the cotton secondary metabolites have high affinities for the three OBPs and AlucCSP1, indicating that these binding proteins more likely play a role in gustation than in olfaction.