Two subclasses of odorant‐binding proteins in Spodoptera exigua display structural conservation and functional divergence

Abstract

Although many studies on lepidopteran pheromone-binding proteins (PBPs)/ general odorant-binding proteins (GOBPs) have been reported, the functional differentiation within and between the two odorant-binding protein (OBP) subclasses is still elusive. Here we conducted a comparative study on three SexiPBPs and two SexiGOBPs in Spodoptera exigua. Results showed that all five SexiPBP/GOBP genes have the same intron numbers and conserved exon/intron splice sites. Reverse transcription PCR results showed that these five SexiPBP/GOBPs were primarily expressed in antennae of both sexes and some were also detected in other tissues. Further, quantitative real-time PCR showed that five SexiPBP/GOBPs had different sex-biased expression patterns, with PBP1 being highly male-biased (5.96-fold difference) and PBP3 slightly female-biased (2.43-fold difference), while PBP2 and two GOBPs were approximately sex-equivalent (the absolute value<1.90-fold difference). Binding assays showed that all three SexiPBPs could bind all six sex pheromone components, but SexiPBP1 had much higher affinities [dissociation constant (Ki ) <1.10 μM] than did the other two SexiPBPs (Ki >1.20 μM). Very intriguingly, SexiGOBP2 displayed even stronger binding to five sex pheromone components (Ki <0.40 μM) than SexiPBP1. In contrast, SexiGOBP1 only exhibited weak binding to three alcohol-pheromone components. Similar results were obtained for tested pheromone analogues. In addition, each of SexiPBP/GOBPs selectively bound some plant odorants with considerable affinities (Ki <10.0 μM). Taken together, of the three SexiPBPs, SexiPBP1 may play the most important role in female sex pheromone reception, and additionally all three SexiPBPs can detect some plant odorants, while SexiGOBP2 may be involved in the detection of female sex pheromones in addition to plant odorants. The results strongly suggest functional differentiation within and between the two OBP sub-classes.

Molecular identification and expression patterns of odorant binding protein and chemosensory protein genes inAthetis lepigone(Lepidoptera: Noctuidae)

“…Five AlPBP/GOBPs displayed higher expression in the adult antennae (especially AlGOBP1 and AlPBP1 ), which is consistent with that reported for PBP/GOBPs in other moths (Liu, Liu & Dong, 2013; Liu et al, 2015b; Zhang et al, 2013). According to recent functional studies of moth PBP/GOBPs (Jin et al, 2014; Liu et al, 2015a; Liu, Liu & Dong, 2013; Sun, Liu & Wang, 2013; Zhu et al, 2016) and D. melanogaster LUSH protein (OBP76a) (Ha & Smith, 2006; Stowers & Logan, 2008; Zhou et al, 2004), we hypothesize that the AlPBP/GOBPs may also play important roles in recognizing the sex pheromones of female moths and some host plant volatiles.…”

“…According to recent functional studies of moth PBP/GOBPs (Jin et al, 2014; Liu et al, 2015a; Liu, Liu & Dong, 2013; Sun, Liu & Wang, 2013; Zhu et al, 2016) and D. melanogaster LUSH protein (OBP76a) (Ha & Smith, 2006; Stowers & Logan, 2008; Zhou et al, 2004), we hypothesize that the AlPBP/GOBPs may also play important roles in recognizing the sex pheromones of female moths and some host plant volatiles. Additionally, there are three male-biased and three female-biased AlOBP genes, indicating that these sex-biased OBPs may participate in the reorganization of female or male sex pheromones, plant volatiles from oviposition sites, or other sex-related odorants, and need further analysis to explore their exact roles such as through fluorescence competitive binding assays (Liu et al, 2015b), CRISPR/Cas9 mediated genome editing (Zhu et al, 2016), and gene mutations (Stowers & Logan, 2008). …”

Identification of odorant‐binding and chemosensory protein genes and the ligand affinity of two of the encoded proteins suggest a complex olfactory perception system in Periplaneta americana

“…Their expression patterns were the same as the those in many moth PBPs. Most of these PBPs presented male antennae‐enriched expression patterns, but were also expressed at certain levels in female antennae (Liu et al ., ; Sun et al ., ; Jin et al ., ). Additionally, moth sex pheromone components also elicited an electrophysiological response in female adults.…”

“…Therefore, we focused on one OBP ( PameOBP24 ) and one CSP ( PameCSP7 ) that were equally expressed in the antennae of both sexes and that were relatively highly expressed amongst the OBPs and CSPs based on our transcriptome data (RPKM values), which indicated that they may facilitate the detection of plant and/or food source odorants in both sexes and play key roles in the olfactory function of both sexes. The functions of the selected OBP and CSP may be like those in some of moth GOBPs, which participate in detecting common plant odorants (Liu et al ., ; Zhou et al ., ) and may be crucial for P. americana to locate different hosts. The two selected genes, PameOBP24 and PameCSP7 , were used to express recombinant proteins to further investigate their odorant affinities in vitro .…”

Molecular and Functional Characterization of Three Odorant-Binding Protein from Periplaneta americana

“…Two important classes of OBPs in Lepidoptera, pheromone binding protein and general odorant binding protein, are primarily expressed in antennae of both sexes and are involved in the detection of sex pheromone components and plant volatiles, respectively, in species such as Helicoverpa armigera [27], Plutella xylostella [28] and Spodoptera exigua [29]. Our qPCR data showed that PameOBP1 and 2 were specifically expressed at high levels in antennae, and showed a strong male bias, suggesting that they might be involved in odorant or pheromone discrimination in P .…”