An odorant‐binding protein of Asian citrus psyllid, Diaphorina citri, participates in the response of host plant volatiles

Abstract

BACKGROUND: Odorant-binding proteins (OBPs) in insects contribute to the sensitivity of the olfactory system and connect external odorants to olfactory receptor neurons. Determination of the chemosensory functions in Diaphorina citri, a vector of the citrus Huanglongbing pathogen, may help in developing a potential target for pest management. RESULTS: Diaphorina citri showed dose-dependent electroantennogram recording (EAG) responses to 12 host plant volatiles. A two-choice behavioral trap experiment showed that four compounds (methyl salicylate, linalool, citral and R-(+)-limonene) that elicited high EAG responses also had significant attraction to adults. The expression profiles induced by these compounds were detected in nine OBP genes, DcitOBP1-9. DcitOBP3, DcitOBP6 and DcitOBP7 commonly showed significant upregulation or downregulation compared with the control. Microscale thermophoresis (MST) showed that the recombinant protein DcitOBP7 had high in vitro binding affinities (K d < 10 ∼M) to methyl salicylate, linalool and R-(+)-limonene, and moderate binding affinity to citral with a K d value of 15.95 ∼M. Furthermore, RNA interference (RNAi)-suppressed messenger RNA (mRNA) expression of DcitOBP7 resulted in a significant reduction in EAG activity and in adult D. citri behavioral responses to tested volatiles and the preferred host, Murraya paniculata. The hydrophilic residue Arg107 of DcitOBP7 may have a key role in binding odorants via formation of hydrogen bonds.CONCLUSION: These results show that DcitOBP7 plays an important role in the olfactory response. This finding may provide new insight into the functions of OBP families in D. citri and aid in the development of safe strategies for managing D. citri populations.

Advances and Challenges in RNA Interference Technology for Citrus Huanglongbing Vector Control

“…The transformant method involves the generation of a transgenic plant (genetically modified organism, GMO) harboring a construct to produce dsRNA targeting the insect mRNA. Meanwhile, the non-transformant delivery methods are GMO-free and include micro-injection of dsRNA directly into the hemolymph [37], topical application on insect body [38,39], soaking insects into a dsRNA solution [40,41], feeding insects with artificial diets containing dsRNA molecules [42][43][44], and feeding insect with plants treated with a dsRNA solution through drenching or trunk injection [45]. Despite the introduction of several dsRNA molecules, however, only those delivery methods that result in insect topical absorption and/or acquisition via feeding are applicable for ACP management in citrus orchards (Table 1).…”

“…RNAi-mediated ACP control has also been tested using feeding assays. Through the ingestion of an artificial diet, several genes including cathepsin D, chitin synthase, inhibitor of apoptosis [55], boule [42], trehalose-6-phosphate synthase [43], and odorant-binding 7 [44], in ACP were silences, leading to a lethal phenotype and/or an abnormal behavioral response. Furthermore, knockdown of the arginine kinase and superoxide dismutase genes through feeding and iPS reduced the ACP adult survival rate [26].…”

EsigGOBP1: The Key Protein Binding Alpha-Phellandrene in Endoclita signifer Larvae

“…The expression of chemosensory genes can be regulated by host plants [ 44 ]. For example, the expression levels of DcitOBP3 , DcitOBP6 and DcitOBP7 were found to change significantly (upregulated or downregulated) in the heads of adult psyllids upon exposure to test volatiles compared with the control [ 45 ]. Similar results were observed in the expressions of AgrnOBPs in the antennae when exposed to semiochemicals [ 45 ].…”

“…For example, the expression levels of DcitOBP3 , DcitOBP6 and DcitOBP7 were found to change significantly (upregulated or downregulated) in the heads of adult psyllids upon exposure to test volatiles compared with the control [ 45 ]. Similar results were observed in the expressions of AgrnOBPs in the antennae when exposed to semiochemicals [ 45 ]. Further, exposure to the plant kairomone, (E)-2-hexenol, specifically induced the expressions of several OBP genes among the 29 OBP s that showed higher expressions in Holotrichia oblita , and this was further confirmed by an in vitro binding assay [ 46 ].…”

Function and Characterization Analysis of BodoOBP8 from Bradysia odoriphaga (Diptera: Sciaridae) in the Recognition of Plant Volatiles and Sex Pheromones

“…As the main olfactory organs of insects, antennae play an important role in behavioral responses, such as searching for hosts, mates, and oviposition sites [23,40,41]. Odorantbinding proteins play an important role in the olfactory system, assisting insect antennae in recognizing and binding to external semiochemicals, which are then delivered to the ORs via the lymph [18,[42][43][44][45]. Hence, determining the expression levels of insect OBP genes in different developmental stages and tissues could help us to predict the physiological functions of these genes in insects.…”