Abstract
Insect chemosensory proteins (CSPs) have been proposed to capture and transport hydrophobic chemicals from air to olfactory receptors in the lymph of antennal chemosensilla. They may represent a new class of soluble carrier protein involved in insect chemoreception. However, their specific functional roles in insect chemoreception have not been fully elucidated. In this study, we report for the first time three novel CSP genes (AlinCSP1-3) of the alfalfa plant bug Adelphocoris lineolatus (Goeze) by screening the antennal cDNA library. The qRT-PCR examinations of the transcript levels revealed that all three genes (AlinCSP1-3) are mainly expressed in the antennae. Interestingly, these CSP genes AlinCSP1-3 are also highly expressed in the 5th instar nymphs, suggesting a proposed function of these CSP proteins (AlinCSP1-3) in the olfactory reception and in maintaining particular life activities into the adult stage. Using bacterial expression system, the three CSP proteins were expressed and purified. For the first time we characterized the types of sensilla in the antennae of the plant bug using scanning electron microscopy (SEM). Immunocytochemistry analysis indicated that the CSP proteins were expressed in the pheromone-sensitive sensilla trichodea and general odorant-sensitive sensilla basiconica, providing further evidence of their involvement in chemoreception. The antennal activity of 55 host-related semiochemicals and sex pheromone compounds in the host location and mate selection behavior of A. lineolatus was investigated using electroantennogram (EAG), and the binding affinities of these chemicals to the three CSPs (AlinCSP1-3) were measured using fluorescent binding assays. The results showed several host-related semiochemicals, (Z)-3-hexen-1-ol, (E)-2-hexen-1-al and valeraldehyde, have a high binding affinity with AlinCSP1-3 and can elicit significant high EAG responses of A. lineolatus antennae. Our studies indicate the three antennae-biased CSPs may mediate host recognition in the alfalfa plant bug A. lineolatus.
Highlights
The number of insect species on the earth, even at a conservative estimate, exceeds one million, which are far more than any other kind of living creatures [1,2]
Expression Profile of AlinCSP1-3 Transcripts We have identified three new chemosensory proteins (CSPs) from the plant bug Adelphocoris lineolatus by constructing and screening the antenna specific cDNA library and named as AlinCSP1, AlinCSP2 and AlinCSP-3 (GenBank No GQ477014-GQ477016)
The chemosensory proteins AlinCSP1-3 of the alfalfa plant bug A. lineolatus showed very high sequence identities with no-Hemipteran CSPs (Figure 2), supporting the view that insect CSPs are highly conserved even across very distant species [17,18,32] and implying important roles they might play in insect physiology
Summary
The number of insect species on the earth, even at a conservative estimate, exceeds one million, which are far more than any other kind of living creatures [1,2]. The alfalfa plant bug Adelphocoris lineolatus (Goeze) (Hemiptera: Miridae) is a wellknown pest in Europe, United States and China This plant bug and several other mirids are extremely herbivores and cause severe damage to many important crops such as beans, strawberries, peaches, cotton, and various seed crops each year [3,4,5]. These mirids are attracted to flowering plants especially cotton, alfalfa and mung bean [3,4,6,7,8,9], suggesting mirids use chemical information from these flowers to forage suitable hosts and find oviposition sites. Identification of attractant molecules and their interactions with olfactory proteins are meaningful for monitoring and mass-trapping these mirids and other insect pest [10,11]
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