Screening of olfactory genes related to blood-feeding behaviors in Culex pipiens quinquefasciatus and Culex pipiens molestus by transcriptome analysis

Abstract

Background Culex pipiens quinquefasciatus Say (Cx. quinquefasciatus) and Culex pipiens form molestus Forskal (Cx. molestus) in the Culex pipiens complex group show considerable differences in host seeking, blood feeding, mating behavior and in vector competence. Blood-feeding mosquito behaviors are closely related to their olfactory gene expression and olfactory gene repertoire composition. Comparing olfactory genes between these two subspecies with significantly different blood-feeding behaviors can support further research on the molecular mechanism of the Culex pipiens complex olfactory sensory system, providing a new approach for determining candidate attractant or repellent compounds. Methods Non-blood-feeding (NBF) and post-blood-feeding (PBF) olfactory system transcriptomes of the two subspecies were sequenced, and the biological functions of their differentially expressed genes were described by bioinformatics analysis. A quantitative polymerase chain reaction (qPCR) was applied to validate the RNA-seq data. The roles of particular olfactory receptors in Cx. quinquefasciatus blood-feeding behaviors were evaluated by RNAi. Results Five, 7, 24, and 3 Cx. quinquefasciatus-specific OBPs, Cx. molestus-specific OBPs, Cx. quinquefasciatus-specific ORs and Cx. molestus-specific ORs were identified, respectively. The majority of selected ORs were consistent with the predicted transcriptome sequencing results after qRT-PCR validation. OR5 was expressed only in Cx. quinquefasciatus, and OR65 was the only gene upregulated after blood feeding in Cx. molestus. The blood-feeding rates of the OR5 and OR78 dsRNA groups were significantly lower (4.3%±3.1% and 13.3%±11.5%) than those of the enhanced green fluorescence protein (EGFP) group (64.5%±8.7%). Conclusion Most OBPs and ORs were expressed in both subspecies but showed divergence in expression level. OR5 and OR65 might be species-specific expressed genes that regulate the olfactory behaviors of Cx. quinquefasciatus and Cx. molestus, respectively. The RNA interference of OR5 and OR78 could inhibit the blood-feeding behavior of Cx. quinquefasciatus, providing new targets for screening effective repellent compounds to control mosquito-borne diseases effectively and efficiently.

Elevated expression of odorant receptors and odorant-binding proteins genes detected in antennae of Culex quinquefasciatus field females

“…Divergence of gene expression pattern for olfactory genes has been observed even for subspecies. In a very recent paper, Gu et al (18) identified genes (OR5 and OR65) that were expressed in a subspecies-specific way and demonstrated through RNA interference that two olfactory genes could inhibit the bloodfeeding behavior of Cx. quinquefasciatus.…”

“…Previous studies indicate that insect OBPs have a modulating effect on olfactory physiology and on behavior linked to specific odorants (10). To characterize the functions of individual olfactory genes, recent studies have been used several techniques to silence these genes and identify their roles in insect behavior (17,18).…”

Identification of differentially expressed genes based on antennae RNA-seq analyses in Culex quinquefasciatus and Culex pipiens molestus

“…quinquefasciatus and Cx. p. molestus [ 12 ], much olfactory gene expression was significantly regulated to affect host seeking and oviposition.…”

“…quinquefasciatus and Cx. p. molestus [12], much olfactory gene expression was significantly regulated to affect host seeking and oviposition. In this study, 15 odor-related genes were found among the DEGs between Cx.…”

“…With the help of proboscis and eyes, which detect taste and visual cues, mosquitoes are successful in flight navigation toward the host [10]. The expressions of many chemoreceptor genes have been found in the antennae of Anopheles sinensis, and their expression levels are significantly regulated after the blood meal [11], quite similar to the antennae of the Culex pipiens complex [12] and Aedes aegypti [13][14][15]. Besides the typical olfactory function, the antennae of mosquitoes are model systems for other sensations, including acoustics [16].…”