Characterization of MaltOBP1, a Minus-C Odorant-Binding Protein, From the Japanese Pine Sawyer Beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae).

Fangmei Zhang,Jing Zhang,Xuguo Zhou,Yunhui Zhang,Austin Merchant,Zhibin Zhao,Qinghua Wang,Xiangrui Li,Qingwen Zhang

doi:10.3389/fphys.2020.00212

Abstract

Insect Odorant-Binding Proteins (OBPs) play crucial roles in the discrimination, binding and transportation of odorants. Herein, the full-length cDNA sequence of Minus-C OBP1 (MaltOBP1) from the Japanese pine sawyer beetle, Monochamus alternatus, was cloned by 3′ and 5′ RACE-PCR and analyzed. The results showed that MaltOBP1 contains a 435 bp open reading frame (ORF) that encodes 144 amino acids, including a 21-amino acid signal peptide at the N-terminus. The matured MaltOBP1 protein possesses a predicted molecular weight of about 14 kDa and consists of six α-helices, creating an open binding pocket, and two disulfide bridges. Immunoblotting results showed that MaltOBP1 was most highly expressed in antennae in both sexes, followed by wings and legs. Fluorescence assays demonstrated that MaltOBP1 protein exhibited high binding affinity with (R)-(+)-α-pinene, (−)-β-pinene, trans-caryophyllene, (R)-(+)-limonene and (–)-verbenone, which are the main volatile compounds of the pine tree. Our combined results suggest that MaltOBP1 plays a role in host seeking behavior in M. alternatus.

Highlights

Insects rely on sophisticated olfaction to detect semiochemicals at critical stages of the life cycle, subsequently undertaking a series of corresponding behavioral responses, such as mating, oviposition, foraging, host seeking and predator avoidance (Zhang et al, 2015; Elgar et al, 2018)
These results provide insight into the mechanism of olfactory recognition of M. alternatus and may assist in the development of new pest-prevention strategies for M. alternatus
Additional experiments, such as gene knockdown studies and site-directed mutagenesis, would be required for further verification of MaltOBP1’s physiological functions

Summary

Introduction

Insects rely on sophisticated olfaction to detect semiochemicals at critical stages of the life cycle, subsequently undertaking a series of corresponding behavioral responses, such as mating, oviposition, foraging, host seeking and predator avoidance (Zhang et al, 2015; Elgar et al, 2018). Many proteins have been found to be involved in odorant reception in major chemosensory organs (Leal, 2013) Among these proteins, odorant-binding proteins (OBPs) are commonly accepted to act as the first step in olfaction in insects (Brito et al, 2016; Pelosi et al, 2018). Insect OBPs belong to a multigene family, which has been categorized into four distinct types according to the number of conserved cysteine residues present. These types are “Classic OBPs” (with six conserved cysteines), “Minus-C OBPs” (with four conserved cysteines), “Plus-C OBPs” (with eight conserved cysteines), and “Atypical OBPs” (with more than eight conserved cysteines) (Venthur et al, 2014; Brito et al, 2016)

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