Abstract
Simple SummaryInsects’ behavior and ecology are closely related to their chemosensory systems, during which odorant receptors (ORs) play an essential role in host recognition. Although OR gene evolution has been studied in many insect orders, a comprehensive evolutionary analysis and expression of OR gene gain and loss events among diverse hemipteran species are still needed. In this study, we identified and analyzed the OR genes from hemipteran species systematically. The number of OR genes discovered in each species ranged from less than ten to hundreds. Gene gain and loss events of OR have occurred in several species in the seven major clades classified through phylogenetic analysis. Then, we discovered the amino acid differences between species to understand the molecular evolution of OR in the order Hemiptera through positive selection. This study lays a foundation for subsequent investigations into the molecular mechanisms of Hemiptera olfactory receptors involved in host recognition.Olfaction is a critical physiologic process for insects to interact with the environment, especially plant-emitted volatiles, during which odorant receptors (ORs) play an essential role in host recognition. Although OR gene evolution has been studied in many insect orders, a comprehensive evolutionary analysis and expression of OR gene gain and loss events among diverse hemipteran species are still required. In this study, we identified and analyzed 887 OR genes from 11 hemipteran species. The number of OR genes discovered in each species ranged from less than ten to hundreds. Phylogenetic analysis revealed that all identified Hemiptera OR genes were classified into seven major clades. Gene gain and loss events of OR have occurred in several species. Then, by positive selection, we discovered the amino acid differences between species to understand the molecular evolution of OR in the order Hemiptera. Additionally, we discussed how evolutionary analysis can aid the study of insect–plant communication. This study lays a foundation for subsequent investigations into the molecular mechanisms of Hemiptera olfactory receptors involved in host recognition.
Highlights
Insect behavior and ecology are closely related to their chemosensory system and are involved in various activities, such as host plant selection, mating, intra-specific communication, and avoidance behaviors [1,2]
By comparing the number of odorant receptors (ORs) genes retrieved in this study with those found in previous studies in Hemiptera, H. halys [39], R. prolixus [12], A. lucorum [17], A. pisum [23], A. gossypii [25], and N. lugens [50], we detected more OR genes than previously reported (Figure 2)
H. halys has specific expansion into Clades Three and Four. We discovered that these two branches were being driven by positive selection, and nine positive selection sites were identified in the OR gene of H. halys in Clade Three
Summary
Insect behavior and ecology are closely related to their chemosensory system and are involved in various activities, such as host plant selection, mating, intra-specific communication, and avoidance behaviors [1,2]. A key step in insect chemosensation is the detection of chemicals by receptor proteins located on the membranes of peripheral sensory neurons, which convert chemical signals into electrical signals that travel into the insect’s central nervous system, resulting in behavioral responses. Chemoreceptors primarily include three main receptor families [3], gustatory receptors (GRs), ionotropic receptors (IRs), and odorant receptors (ORs). IRs mainly detect acids and amines [7], and ORs are key receptors involved in the detection of volatile compounds, including host plant volatiles [6]. The insect odorant receptors are seven-transmembrane domain proteins [8] that are classified into an odorant receptor co-receptor (Orco) and conventional ORx. The Orco and ORx form a heterotetrameric receptor complex on the membrane of olfactory sensory neurons, which is involved in olfactory recognition [9,10].
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