The diverse small proteins called odorant-binding proteins

Insecticidal Activity of Fatty Acids From the Fruit Extract of Momordica cymbalaria Fenzl Ex Naudin, Has Insecticidal Activities on Mosquito Larvae

The fruit and other parts of Momordica cymbalaria are known to have medicinal properties. The study investigates the chemical composition and functional groups of M. cymbalaria fruits to assess the insecticidal potential of its bioactive metabolites. In silico approach was used to understand the mechanism behind the insecticidal nature of these metabolites. Ethyl acetate extract has 18 compounds, whereas 20 compounds were identified in methanol using gas chromatography-mass spectroscopy analysis. The extracts contain several functional groups, including alkanes, esters, carboxylic acids, amides and aromatic groups. The insecticidal bioassay using methanol and ethyl acetate extracts of M. cymbalaria on Aedes aegypti and Culex quinquefasciatus mosquito larvae shows that the LC50 value for A. aegypti was 65.7 ppm, for C. quinquefasciatus was 96.9 ppm and for ethyl acetate and methanol extract is 282.36 and 388.09 ppm. Molecular docking of secondary metabolites was performed with five insect proteins, namely, odorant binding protein (OBP), cytochrome P450 (CYP450), prophenol oxidase (PPO), arylalkylamine n-acetyltransferease (aaNAT) and sterol carrier protein (SCP). Results show that methyl 6-cis, 9-cis, 11-trans-octadecatrienoate has high binding affinity with sterol carrier protein (SCP-2) besides showing binding with other insect proteins. The data suggest that methyl 6-cis, 9-cis, 11-trans-octadecatrienoate has multiple insecticidal actions and may serve as a green insecticide.

Structural Rearrangement of the Olfactory Epithelium in Male Baikal Yellowfin Sculpins Across the Reproductive Period

The morphological peculiarities of receptor neurons and support cells in the olfactory epithelium of male yellowfin sculpin (Cottocomephorus grewingkii; Dybowski, 1874) were studied during the pre-spawning, spawning (when males do not feed and have a higher sensitivity to female pheromones), and guarding (the fertilized eggs) periods. This study was performed using electron transmission and laser confocal microscopy. Structural changes in the fish olfactory epithelium are associated with the shift in olfactory signals from alimentary to pheromonal. These results expand our knowledge of the odorant-dependent plasticity of the periphery of the fish olfactory system.

Identification and optimization of volatile organic compounds to enhance bait attractiveness for red imported fire ants (Solenopsis invicta Buren)

BACKGROUND

The red imported fire ant (RIFA, Solenopsis invicta), a highly destructive invasive pest, has rapidly spread through human trade, posing significant threats to agricultural and forest ecosystems. Due to its preference for high-fat and high-protein foods, ham sausage is commonly used as bait to monitor RIFA populations in invaded areas. However, the presence of volatile organic compounds (VOCs) in such baits may affect their effectiveness because VOCs can act as either attractants or repellents. Identifying VOCs that specifically attract RIFA is essential to improve bait efficacy.

RESULTS

This study aimed to identify attractant compounds within bait VOCs for RIFA, leveraging the highly-expressed antennal odorant-binding protein 1 (OBP1) and reverse chemical ecology approach. Additionally, we examined the effects of mixtures of these attractants on RIFA behavior. Our findings revealed that anethole, 1S-(-)-β-pinene, and β-caryophyllene individually attracted RIFA at 0.1 μg/μL. Notably, a combination of anethole and 1S-(-)-β-pinene enhanced behavioral activity more than individual compounds, suggesting synergistic effects. Conversely, the addition of β-caryophyllene to anethole significantly reduced RIFA activity. These results provide a theoretical basis for developing behavioral regulators targeting RIFA.

CONCLUSION

This study demonstrates that the integration of OBP-based in vitro assays with computational simulations can effectively identify behaviorally active compounds for RIFA. Additionally, it clarifies the optimal ratios of active VOCs in baits, offering valuable theoretical guidance for enhancing RIFA population monitoring efforts. © 2025 Society of Chemical Industry.

Identification of Candidate Olfactory Genes in the Antennal Transcriptome of Loxostege sticticalis Trapped by Three Different Sex Pheromone Blends

Insects sense intraspecific or interspecific information about the chemical substances in the habitat through the sensitive olfactory system to carry out foraging, mating, oviposition, and other activities. The antennae serve as the primary olfactory organs in insects. The olfactory process involves the participation of many proteins, such as odorant-binding proteins (OBPs) and odorant receptors (ORs), but ORs play a central role in olfactory specificity and sensitivity. The beet webworm, Loxostege sticticalis, is an omnivorous agricultural pest that endangers crops and poses a significant risk to the agricultural and animal husbandry production in northern China. In this study, Illumina sequencing was conducted on the antennal transcriptome of male L. sticticalis trapped by three different sex pheromone blends. A total of 10,320 DEGs were identified, from which 46 candidate olfactory genes were selected for further analysis. These candidate olfactory genes comprise 13 odorant receptors, 6 ionotropic receptors (IRs), 3 gustatory receptors (GRs), 12 odorant-binding proteins, and 13 chemosensory proteins (CSPs). In summary, we analyzed the antennal transcriptome of male L. sticticalis trapped by three different sex pheromone blends and identified several candidate olfactory genes. This discovery offers a foundation for further molecular-level investigations into the olfactory system of L. sticticalis.

Key site residues of Cnaphalocrocis medinalis odorant-binding protein 13 CmedOBP13 involved in interacting with rice plant volatiles

Odorant binding proteins (OBPs) play key roles in the insect olfactory system by assisting the neuronal response to hydrophobic odor molecules, understanding their interaction with ligands will facilitate the virtual screening of behaviorally active compounds in insects. Here, we successfully cloned and confirmed CmedOBP13, an antennae-biased OBP from the rice leaffolder Cnaphalocrocis medinalis, as a secreted protein. Recombinant CmedOBP13 was obtained using the Escherichia coli system, and its binding affinities to 35 volatile compounds emitted by rice plants and three sex pheromone components from female moths were assessed by a competitive binding assay. The results revealed that CmedOBP13 exhibited binding affinity to 23 rice volatiles, while no binding affinity for sex pheromone components. Furthermore, the stability of its conformation was found to be dependent on the pH level. Finally, the interaction between CmedOBP13 and odorants was predicted and confirmed by molecular docking and mutation functional assays, respectively. The combination of multiple hydrophobic residues created an adequate hydrophobic setting for ligands, and three residues (Glu13, Arg34, and Tyr115) might form hydrogen bonds with 15 odorants. Single mutations of Glu13, Arg34, Leu72, and Tyr115 diminished the binding affinities of CmedOBP13 to corresponding odorants, respectively. These findings provided valuable insights into the mode of action of CmedOBP13 interacting with the volatiles of rice plants and will guide the screening of behaviorally active compounds against C. medinalis in future.

An integrated anatomical, functional and evolutionary view of the Drosophila olfactory system

The Drosophila melanogaster olfactory system is one of the most intensively studied parts of the nervous system in any animal. Composed of ~60 independent olfactory neuron classes, with several associated hygrosensory and thermosensory pathways, it has been subject to diverse types of experimental analyses. However, synthesizing the available data is limited by the incompleteness and inconsistent nomenclature found in the literature. In this work, we first "complete" the peripheral sensory map through the identification of a previously uncharacterized antennal sensory neuron population expressing Or46aB, and the definition of an exceptional "hybrid" olfactory neuron class comprising functional Or and Ir receptors. Second, we survey developmental, anatomical, connectomic, functional and evolutionary studies to generate an integrated dataset of these sensory neuron pathways - and associated visualizations - creating an unprecedented comprehensive resource. Third, we illustrate the utility of the dataset to reveal relationships between different organizational properties of this sensory system, and the new questions these stimulate. These examples emphasize the power of this resource to promote further understanding of the construction, function and evolution of these neural circuits.

Cracking the plant VOC sensing code and its practical applications

Volatile organic compounds (VOCs) are essential airborne mediators of interactions between plants. These plant-plant interactions require sophisticated VOC-sensing mechanisms that enable plants to regulate their defenses against pests. However, these interactions are not limited to specific plants or even conspecifics, and can function in very flexible interactions between plants. Sensing and responding to VOCs in plants is finely controlled by their uptake and transport systems as well as by cellular signaling via, for example, chromatin remodeling system-based transcriptional regulation for defense gene activation. Based on the accumulated knowledge about the interactions between plants and their major VOCs, companion plants and biostimulants are being developed for practical applications in agricultural and horticultural pest control, providing a sustainable alternative to harmful chemicals.

Identification and odor exposure regulation of odorant-binding proteins in Picromerus lewisi

The highly developed sensitive olfactory system is essential for Picromerus lewisi Scott (Hemiptera: Pentatomidae) adults, an widely distributed natural predatory enemy, to locate host plants. During this process, odorant-binding proteins (OBPs) are thought to have significant involvement in the olfactory recognition. However, the roles of OBPs in the olfactory perception of P. lewisi are not frequently reported. Here, we conducted odor exposure and transcriptome sequencing experiments using healthy and Spodoptera litura-infested tobacco plants as odor sources. The transcriptomic data revealed that the alteration in the expression of mRNA levels upon exposure to odor was sex-dependent. As the expression profiles differed significantly between male and female adults of P. lewisi. A total of 15 P. lewisi OBPs (PlewOBPs) were identified from the P. lewisi transcriptome. Sequence and phylogenetic analysis indicated that PlewOBPs can be classified into two subfamilies (classic OBP and plus-C OBP). The qRT-PCR results showed that the transcript abundance of 8 PlewOBPs substantially altered following exposure to S. litura-infested tobacco plants, compared to the blank control or healthy plants. This implies that these PlewOBPs may have an olfactory function in detecting S. litura-infested tobacco plants. This study establishes the foundation for further understanding of the olfactory recognition mechanism of P. lewisi and helps discover novel targets for functional characterization in future research.

Trans regulation of an odorant binding protein by a proto-Y chromosome affects male courtship in house fly

The male-limited inheritance of Y chromosomes favors alleles that increase male fitness, often at the expense of female fitness. Determining the mechanisms underlying these sexually antagonistic effects is challenging because it can require studying Y-linked alleles while they still segregate as polymorphisms. We used a Y chromosome polymorphism in the house fly, Musca domestica, to address this challenge. Two male determining Y chromosomes (YM and IIIM) segregate as stable polymorphisms in natural populations, and they differentially affect multiple traits, including male courtship performance. We identified differentially expressed genes encoding odorant binding proteins (in the Obp56h family) as candidate agents for the courtship differences. Through network analysis and allele-specific expression measurements, we identified multiple genes on the house fly IIIM chromosome that could serve as trans regulators of Obp56h gene expression. One of those genes is homologous to Drosophila melanogaster CG2120, which encodes a transcription factor that binds near Obp56h. Upregulation of CG2120 in D. melanogaster nervous tissues reduces copulation latency, consistent with this transcription factor acting as a negative regulator of Obp56h expression. The transcription factor gene, which we name speed date, demonstrates a molecular mechanism by which a Y-linked gene can evolve male-beneficial effects.

Three odorant-binding proteins of small hive beetles, Aethina tumida, participate in the response of bee colony volatiles

Aethina tumida (small hive beetle, SHB) is a rapidly spreading invasive parasite of bee colonies. The olfactory system plays a key role in insect behavior, and odorant-binding proteins (OBPs) are involved in the first step of the olfactory signal transduction pathway and the detection of host volatiles. However, the olfactory mechanism of OBPs in SHB-localized bee colonies is unclear. In this study, electroantennogram (EAG) and behavioral bioassay showed that only three compounds (2-heptanone, ocimene, and ethyl palmitate) from bee colonies triggered high electrophysiological and behavioral responses. Three antenna-specific OBP genes (OBP6, OBP11, and OBP19) were identified, and they were significantly expressed on adult days 6-7. Furthermore, by combining RNA interference (RNAi) with EAG, olfactometer bioassay, competitive fluorescence binding assays, and molecular docking, we found that these three OBP genes were involved in the recognition of 2-heptanone and ethyl palmitate, and AtumOBP6 is also involved in the recognition of ocimene. These data indicate that AtumOBP6, AtumOBP11, and AtumOBP19 play an important role in the olfactory response to bee colony volatiles. Our results provide new insights into the functions of the OBP families in A. tumida and help to explore more potential target genes for environmentally friendly pest control strategies.

CRISPR/Cas9-Based Genome Editing of Fall Armyworm (Spodoptera frugiperda): Progress and Prospects

The fall armyworm (Spodoptera frugiperda) poses a substantial threat to many important crops worldwide, emphasizing the need to develop and implement advanced technologies for effective pest control. CRISPR/Cas9, derived from the bacterial adaptive immune system, is a prominent tool used for genome editing in living organisms. Due to its high specificity and adaptability, the CRISPR/Cas9 system has been used in various functional gene studies through gene knockout and applied in research to engineer phenotypes that may cause economical losses. The practical application of CRISPR/Cas9 in diverse insect orders has also provided opportunities for developing strategies for genetic pest control, such as gene drive and the precision-guided sterile insect technique (pgSIT). In this review, a comprehensive overview of the recent progress in the application of the CRISPR/Cas9 system for functional gene studies in S. frugiperda is presented. We outline the fundamental principles of applying CRISPR/Cas9 in S. frugiperda through embryonic microinjection and highlight the application of CRISPR/Cas9 in the study of genes associated with diverse biological aspects, including body color, insecticide resistance, olfactory behavior, sex determination, development, and RNAi. The ability of CRISPR/Cas9 technology to induce sterility, disrupt developmental stages, and influence mating behaviors illustrates its comprehensive roles in pest management strategies. Furthermore, this review addresses the limitations of the CRISPR/Cas9 system in studying gene function in S. frugiperda and explores its future potential as a promising tool for controlling this insect pest.

Identification and sex expression profiles of candidate chemosensory genes from Atherigona orientalis via the antennae and leg transcriptome analysis

Atherigona orientalis Schiner (1868) is an acknowledged agricultural pest owing to its feeding habits and breeding locations. This insect is a tropical and subtropical pest in fruits and vegetables, in which >50 varieties of fruits and vegetables in 26 families, such as Capsicum annuum, Lycopersicon esculentum, and Cucumis melo have been attacked. Moreover, A. orientalis may also develop in rotten crops and feces or insect carcasses, which are also considered one kind of sanitary pest and medical insect. At present, the invasion ranges of A. orientalis are still increasing and more preventive and management measures are to be processed. To gain a better understanding of the molecular mechanisms involved in olfactory reception in A. orientalis, the transcriptome of male and female antennae and legs was systematically analyzed. In total, 131 chemosensory-related genes, including 63 odorant receptors (ORs), 20 gustatory receptors (GRs), 18 ionotropic receptors (IRs), 27 odorant binding proteins (OBPs), 1 chemosensory protein (CSP), and 2 sensory neuron membrane proteins (SNMPs), were identified. The analysis focused on obtaining expression information of candidate olfactory genes at the transcriptomic level by examining the differentially expressed genes (DEGs) in all samples. Totally, 41 DEGs were identified between male antennae (MA) and female antennae (FA), including 32 ORs, 5 OBPs, 1 IR, 2 GRs and 1 SNMP. In MA versus male legs (ML), 78 DEGs were identified (45 ORs, 18 OBPs, 6 GRs, 6 IRs, 1 CSP and 2 SNMPs). In FA and female legs (FL), 96 DEGs were identified (51 ORs, 21 OBPs, 9 GRs, 12 IRs, 1 CSP and 2 SNMPs). For ML and FL, 3 DEGs were identified, including 2 ORs and 1 SNMP. Our results supplement valuable insights for future research on the chemoreception mechanisms in A. orientalis.

Molecular and cellular organization of odorant binding protein genes in Drosophila

Chemosensation is important for the survival and reproduction of animals. The odorant binding proteins (OBPs) are thought to be involved in chemosensation together with chemosensory receptors. While OBPs were initially considered to deliver hydrophobic odorants to olfactory receptors in the aqueous lymph solution, recent studies suggest more complex roles in various organs. Here, we use GAL4 transgenes to systematically analyze the expression patterns of all 52 members of the Obp gene family and 3 related chemosensory protein genes in adult Drosophila, focusing on chemosensory organs such as the antenna, maxillary palp, pharynx, and labellum, and other organs such as the brain, ventral nerve cord, leg, wing, and intestine. The OBPs were observed to express in diverse organs and in multiple cell types, suggesting that these proteins can indeed carry out diverse functional roles. Also, we constructed 10 labellar-expressing Obp mutants, and obtained behavioral evidence that these OBPs may be involved in bitter sensing. The resources we constructed should be useful for future Drosophila OBP gene family research.

Role of odorant binding protein C12 in the response of Tribolium castaneum to chemical agents

Tribolium castaneum is a worldwide pest of stored grain that mainly damages flour, and not only causes serious loss of flour quality but also leads to deterioration of flour quality. Chemical detection plays a key role in insect behavior, and the role of odorant-binding proteins (OBPs) in insect chemical detection has been widely studied. OBPs can interact with small molecule compounds and thereby modulate variation in insecticide susceptibility in insects. In this study, a total of 65 small molecule compounds are selected to investigate the bound effect with TcOBP C12. The molecular docking results showed that β-caryophyllene, (-)-catechin, butylated hydroxytoluene, diphenyl phthalate and quercetin were the top five compounds, with docking binding energies of -6.11, -5.25, -5.09, -5.05, and - 5.03 Kcal/mol, respectively. Molecular dynamics analysis indicated that odorant binding protein C12 (TcOBP C12) exhibited high binding affinity to all five tested chemical ligands, evidenced by fluorescence quenching assay in vitro. In addition, the contact toxicity assay results suggested that these chemical agents caused a dose-dependent increase in mortality rate for T. castaneum adults. The TcOBP C12 gene was upregulated >2 times after a 24-h exposure, indicating that OBP C12 may play an important role for T. castaneum in response to these chemical agents. In conclusion, our results provide a theoretical basis for future insecticide experiments and pest management.

Genetic and behavioral differences between above and below ground Culex pipiens bioforms

Efficiency of mosquito-borne disease transmission is dependent upon both the preference and fidelity of mosquitoes as they seek the blood of vertebrate hosts. While mosquitoes select their blood hosts through multi-modal integration of sensory cues, host-seeking is primarily an odor-guided behavior. Differences in mosquito responses to hosts and their odors have been demonstrated to have a genetic component, but the underlying genomic architecture of these responses has yet to be fully resolved. Here, we provide the first characterization of the genomic architecture of host preference in the polymorphic mosquito species, Culex pipiens. The species exists as two morphologically identical bioforms, each with distinct avian and mammalian host preferences. Cx. pipiens females with empirically measured host responses were prepared into reduced representation DNA libraries and sequenced to identify genomic regions associated with host preference. Multiple genomic regions associated with host preference were identified on all 3 Culex chromosomes, and these genomic regions contained clusters of chemosensory genes, as expected based on work in Anopheles gambiae complex mosquitoes and in Aedes aegypti. One odorant receptor and one odorant binding protein gene showed one-to-one orthologous relationships to differentially expressed genes in A. gambiae complex members with divergent host preferences. Overall, our work identifies a distinct set of odorant receptors and odorant binding proteins that may enable Cx. pipiens females to distinguish between their vertebrate blood host species, and opens avenues for future functional studies that could measure the unique contributions of each gene to host preference phenotypes.

Odorant binding protein 18 increases the pathogen resistance of the imported willow leaf beetle, Plagiodera versicolora

Background

Insect odorant-binding proteins (OBPs) are a class of small molecular weight soluble proteins. In the past few years, OBPs had been found to work as carriers of ligands and play a crucial role in olfaction and various other physiological processes, like immunity. A subset of insect OBPs had been found to be expressed differently and play a function in immunity of fungal infection. However, there are few studies on the role of OBPs in immunity of bacterial infection.

Methods

To identify the immune-related OBPs of Plagiodera versicolora after infected by Pseudomonas aeruginosa, we determined the mortality of P. versicolora to P. aeruginosa and selected the time point of 50% mortality of larvae to collect samples for RNA-seq. RNAi technology was used to investigate the function of immune-related OBPs after P. aeruginosa infection.

Results

RNA-seq data shows that PverOBP18 gene significantly up-regulated by 1.8-fold and further RT-qPCR affirmed its expression. Developmental expression profile showed that the expression of PverOBP18 was highest in the pupae, followed by the female adults, and lower in the 1st-3rd larvae and male adults with lowest in eggs. Tissue expression profiling showed that PverOBP18 was dominantly expressed in the epidermis. RNAi knockdown of PverOBP18 significantly reduced the expression of bacterial recognition receptor gene PGRP and antibacterial peptide gene Attacin and reduced the resistance of P. versicolora to P. aeruginosa infection.

Conclusion

Our results indicated that PverOBP18 gene increased the pathogen resistance of P. versicolora by cooperating with the immune genes and provided valuable insights into using OBPs as targets to design novel strategies for management of P. versicolora.

Insights on reproduction-related genes in the striped fruit fly, Zeugodacus scutellata (Hendel) (Diptera: Tephritidae)

The striped fruit fly, Zeugodacus scutellata is a significant pest in East and Southeast Asia by damaging Cucurbitaceae blossoms and fruits. To control this pest, a novel strategy to suppress the gene(s) associated with sexually dimorphic phenotypes has been devised and implemented in a laboratory scale. However, comprehensive transcriptomic analysis related to this sex differentiation of Z. scutellata was necessary to determine effective target genes for the genetic control. We performed de novo assembly of the transcript obtained by paired-end sequencing using an Illumina HiSeq platform and let to 217,967 unigenes (i.e., unique genes) with a minimum length of 200 bp. The female produced 31, 604, 442 reads with 97.93% of Q20, 94.76% of Q30, and the male produced 130, 592, 828 reads with 97.93% of Q20 and 94.76 of Q30%. The differentially expressed genes were used to predict genetic factors associated with sex differentiation, which included Rho1, extra-macrochaetae (emc), hopscotch (hop), doublesex (dsx), sex-lethal (sxl), transformer-2 (tra-2), testis-specific serine/threonine-protein kinase (tssk1), tektin1 (tkt1) and 2 (tkt2), odorant binding proteins (OBPs), fruitless (fru), vitellogenin receptor, and hormone receptors in Z. scutellata. In addition, this transcriptome analysis provides the additional gene associated with sex determination and mating behaviors, which would be applied to develop a novel sterile insect technique against Z. scutellata.

An insect chemosensory protein facilitates locust avoidance to fungal pathogens via recognition of fungal volatiles

Locusts (Locusta migratoria) are one of the most destructive insect pests worldwide. Entomopathogenic fungi can infect and kill locusts, with Metarhizium acridum having evolved as a specialized acridid pathogen. However, locusts have evolved countermeasures to limit or avoid microbial pathogens, although the underlying molecular mechanisms behind these defenses remain obscure. Here, we demonstrate that L. migratoria exhibit avoidance behaviors towards M. acridum contaminated food via recognition of fungal volatiles, with locust perception of the volatile mediated by the LmigCSP60 chemosensory protein. RNAi-knockdown of LmigCSP60 lowered locust M. acridum avoidance behavior and increased infection and mortality. The fungal volatile, 2-phenylethanol (PEA), was identified to participate in locust behavioral avoidance. RNAi-knockdown of LmigCSP60 reduced antennal electrophysiological responses to PEA and impaired locust avoidance to the compound. Purified LmigCSP60 was able to bind a set of fungal volatiles including PEA. Furthermore, reduction of PEA emission by M. acridum via construction of a targeted gene knockout mutant of the alcohol dehydrogenase gene (ΔMaAdh strain) that contributes to PEA production reduced locust avoidance behavior towards the pathogen. These findings identify an olfactory circuit used by locusts to detect and avoid potential microbial pathogens before they are capable of initiating infection and highlight behavioral and olfactory adaptations affecting the co-evolution of host-pathogen interactions.

The seminal odorant binding protein Obp56g is required for mating plug formation and male fertility in Drosophila melanogaster

In Drosophila melanogaster and other insects, the seminal fluid proteins (SFPs) and male sex pheromones that enter the female with sperm during mating are essential for fertility and induce profound post-mating effects on female physiology. The SFPs in D. melanogaster and other taxa include several members of the large gene family known as odorant binding proteins (Obps). Work in Drosophila has shown that some Obp genes are highly expressed in the antennae and can mediate behavioral responses to odorants, potentially by binding and carrying these molecules to odorant receptors. These observations have led to the hypothesis that the seminal Obps might act as molecular carriers for pheromones or other compounds important for male fertility, though functional evidence in any species is lacking. Here, we used functional genetics to test the role of the seven seminal Obps in D. melanogaster fertility and the post-mating response (PMR). We found that Obp56g is required for male fertility and the induction of the PMR, whereas the other six genes are dispensable. We found males lacking Obp56g fail to form a mating plug in the mated female's reproductive tract, leading to ejaculate loss and reduced sperm storage, likely due to its expression in the male ejaculatory bulb. We also examined the evolutionary history of these seminal Obp genes, as several studies have documented rapid evolution and turnover of SFP genes across taxa. We found extensive lability in gene copy number and evidence of positive selection acting on two genes, Obp22a and Obp51a. Comparative RNAseq data from the male reproductive tract of multiple Drosophila species revealed that Obp56g shows high male reproductive tract expression in a subset of taxa, though conserved head expression across the phylogeny. Together, these functional and expression data suggest that Obp56g may have been co-opted for a reproductive function over evolutionary time.

Identification of the Major Protein Components of Human and Cow Saliva

Cows produce saliva in very large quantities to lubricate and facilitate food processing. Estimates indicate an amount of 50-150 L per day. Human saliva has previously been found to contain numerous antibacterial components, such as lysozyme, histatins, members of the S-100 family and lactoferrin, to limit pathogen colonization. Cows depend on a complex microbial community in their digestive system for food digestion. Our aim here was to analyze how this would influence the content of their saliva. We therefore sampled saliva from five humans and both nose secretions and saliva from six cows and separated the saliva on SDS-PAGE gradient gels and analyzed the major protein bands with LC-MS/MS. The cow saliva was found to be dominated by a few major proteins only, carbonic anhydrase 6, a pH-stabilizing enzyme and the short palate, lung and nasal epithelium carcinoma-associated protein 2A (SPLUNC2A), also named bovine salivary protein 30 kDa (BSP30) or BPIFA2B. This latter protein has been proposed to play a role in local antibacterial response by binding bacterial lipopolysaccharides (LPSs) and inhibiting bacterial growth but may instead, according to more recent data, primarily have surfactant activity. Numerous peptide fragments of mucin-5B were also detected in different regions of the gel in the MS analysis. Interestingly, no major band on gel was detected representing any of the antibacterial proteins, indicating that cows may produce them at very low levels that do not harm the microbial flora of their digestive system. The nose secretions of the cows primarily contained the odorant protein, a protein thought to be involved in enhancing the sense of smell of the olfactory receptors and the possibility of quickly sensing potential poisonous food components. High levels of secretory IgA were also found in one sample of cow mouth drippings, indicating a strong upregulation during an infection. The human saliva was more complex, containing secretory IgA, amylase, carbonic anhydrase 6, lysozyme, histatins and a number of other less abundant proteins, indicating a major difference to the saliva of cows that show very low levels of antibacterial components, most likely to not harm the microbial flora of the rumen.

Activity of Single Insect Olfactory Receptors Triggered by Airborne Compounds Recorded in Self-Assembled Tethered Lipid Bilayer Nanoarchitectures

Membrane proteins are among the most difficult to study as they are embedded in the cellular membrane, a complex and fragile environment with limited experimental accessibility. To study membrane proteins outside of these environments, model systems are required that replicate the fundamental properties of the cellular membrane without its complexity. We show here a self-assembled lipid bilayer nanoarchitecture on a solid support that is stable for several days at room temperature and allows the measurement of insect olfactory receptors at the single-channel level. Using an odorant binding protein, we capture airborne ligands and transfer them to an olfactory receptor from Drosophila melanogaster (OR22a) complex embedded in the lipid membrane, reproducing the complete olfaction process in which a ligand is captured from air and transported across an aqueous reservoir by an odorant binding protein and finally triggers a ligand-gated ion channel embedded in a lipid bilayer, providing direct evidence for ligand capture and olfactory receptor triggering facilitated by odorant binding proteins. This model system presents a significantly more user-friendly and robust platform to exploit the extraordinary sensitivity of insect olfaction for biosensing. At the same time, the platform offers a new opportunity for label-free studies of the olfactory signaling pathways of insects, which still have many unanswered questions.

Roles of insect odorant binding proteins in communication and xenobiotic adaptation

Odorant binding proteins (OBPs) are small water-soluble proteins mainly associated with olfaction, facilitating the transport of odorant molecules to their relevant receptors in the sensillum lymph. While traditionally considered essential for olfaction, recent research has revealed that OBPs are engaged in a diverse range of physiological functions in modulating chemical communication and defense. Over the past 10 years, emerging evidence suggests that OBPs play vital roles in purifying the perireceptor space from unwanted xenobiotics including plant volatiles and pesticides, potentially facilitating xenobiotic adaptation, such as host location, adaptation, and pesticide resistance. This multifunctionality can be attributed, in part, to their structural variability and effectiveness in transporting, sequestering, and concealing numerous hydrophobic molecules. Here, we firstly overviewed the classification and structural properties of OBPs in diverse insect orders. Subsequently, we discussed the myriad of functional roles of insect OBPs in communication and their adaptation to xenobiotics. By synthesizing the current knowledge in this field, our review paper contributes to a comprehensive understanding of the significance of insect OBPs in chemical ecology, xenobiotic adaptation, paving the way for future research in this fascinating area of study.

Identification of essential oil phytocompounds as natural inhibitors of Odorant-binding protein to prevent malaria through in silico approach

Malaria predominantly affects millions annually in the African and Asian tropical and subtropical countries. With no effective vaccine, malaria prevention is exclusively dependent on preventing human-vector interaction. Anopheles gambiae, the main vector of the malaria parasite Plasmodium falciparum contains Odorant Binding proteins (OBPs) which are considered an attractive drug target for anti-malarial therapy. To identify a potential anti-malarial compound, we performed a structure-based screening of 876 phytocompounds derived from essential oils against the OBP4 by molecular docking. The compounds having better docking scores were assessed for drug-likeness, toxicity, and molecular interaction analysis. As per the results, strong affinities and high stability were demonstrated by two phytocompounds viz. Alpha-cyperone (-8.1 kcal mol-1) and Humulene oxide (-8.1 kcal mol-1) with OBP4. The hydrophobic interactions involve Phe123, Ala106, Thr57, Ala52, Thr69, and Ile64 within the binding cavities, which may block the OBP4 receptor resulting in disorientation. After that, the potential compounds were subjected to molecular dynamics (MD) simulation to evaluate their structural stability and dynamics at the active site of OBP4. The MM-PBSA result revealed that Alpha-cyperone and Humulene oxide had binding free energy of -92.44 kJ mol-1 and -113.25 kJ mol-1, respectively. Simulation outcomes demonstrate that these phytocompounds displayed considerable significant structural and pharmacological properties. The LD50 value of Alpha-cyperone and Humulene oxide also suggested that both are safe and suitable for use in natural repellent development. We suggest that the use of these compounds can minimize the treatment period and the various side effects associated with the currently available anti-malarial drugs.Communicated by Ramaswamy H. Sarma.

Neuronal expression in Drosophila of an evolutionarily conserved metallophosphodiesterase reveals pleiotropic roles in longevity and odorant response

Evolutionarily conserved genes often play critical roles in organismal physiology. Here, we describe multiple roles of a previously uncharacterized Class III metallophosphodiesterase in Drosophila, an ortholog of the MPPED1 and MPPED2 proteins expressed in the mammalian brain. dMpped, the product of CG16717, hydrolyzed phosphodiester substrates including cAMP and cGMP in a metal-dependent manner. dMpped is expressed during development and in the adult fly. RNA-seq analysis of dMppedKO flies revealed misregulation of innate immune pathways. dMppedKO flies showed a reduced lifespan, which could be restored in Dredd hypomorphs, indicating that excessive production of antimicrobial peptides contributed to reduced longevity. Elevated levels of cAMP and cGMP in the brain of dMppedKO flies was restored on neuronal expression of dMpped, with a concomitant reduction in levels of antimicrobial peptides and restoration of normal life span. We observed that dMpped is expressed in the antennal lobe in the fly brain. dMppedKO flies showed defective specific attractant perception and desiccation sensitivity, correlated with the overexpression of Obp28 and Obp59 in knock-out flies. Importantly, neuronal expression of mammalian MPPED2 restored lifespan in dMppedKO flies. This is the first description of the pleiotropic roles of an evolutionarily conserved metallophosphodiesterase that may moonlight in diverse signaling pathways in an organism.

A mosquito-specific antennal protein is critical for the attraction to human odor in the malaria vector Anopheles gambiae

Mosquitoes rely mainly on the sense of smell to decipher their environment and locate suitable food sources, hosts for blood feeding and oviposition sites. The molecular bases of olfaction involve multigenic families of olfactory proteins that have evolved to interact with a narrow set of odorants that are critical for survival. Understanding the complex interplay between diversified repertoires of olfactory proteins and ecologically-relevant odorant signals, which elicit important behaviors, is fundamental for the design of novel control strategies targeting the sense of smell of disease vector mosquitoes. Previously, large multigene families of odorant receptor and ionotropic receptor proteins, as well as a subset of odorant-binding proteins have been shown to mediate the selectivity and sensitivity of the mosquito olfactory system. In this study, we identify a mosquito-specific antennal protein (MSAP) gene as a novel molecular actor of odorant reception. MSAP is highly conserved across mosquito species and is transcribed at an extremely high level in female antennae. In order to understand its role in the mosquito olfactory system, we generated knockout mutant lines in Anopheles gambiae, and performed comparative analysis of behavioral and physiological responses to human-associated odorants. We found that MSAP promotes female mosquito attraction to human odor and enhances the sensitivity of the antennae to a variety of odorants. These findings suggest that MSAP is an important component of the mosquito olfactory system, which until now has gone completely unnoticed.

Gain control in olfactory receptor neurons and the detection of temporal fluctuations in odor concentration

The ability of the cockroach to locate an odor source in still air suggests that the temporal dynamic of odor concentration in the slowly expanding stationary plume alone is used to infer odor source distance and location. This contradicts with the well-established view that insects use the wind direction as the principle directional cue. This contribution highlights the evidence for, and likely functional relevance of, the capacity of the cockroach's olfactory receptor neurons to detect and process-from one moment to the next-not only a succession of odor concentrations but also the rates at which concentration changes. This presents a challenge for the olfactory system because it must detect and encode the temporal concentration dynamic in a manner that simultaneously allows invariant odor recognition. The challenge is met by a parallel representation of odor identity and concentration changes in a dual pathway that starts from olfactory receptor neurons located in two morphologically distinct types of olfactory sensilla. Parallel processing uses two types of gain control that simultaneously allocate different weight to the instantaneous odor concentration and its rate of change. Robust gain control provides a stable sensitivity for the instantaneous concentration by filtering the information on fluctuations in the rate of change. Variable gain control, in turn, enhances sensitivity for the concentration rate according to variations in the duration of the fluctuation period. This efficiently represents the fluctuation of concentration changes in the environmental context in which such changes occur.

SDS-PAGE-Based Quantitative Assay of Hemolymph Proteins in Honeybees: Progress and Prospects for Field Application

In human and veterinary medicine, serum proteins are considered to be useful biomarkers for assessing the health and nutritional status of the organism. Honeybee hemolymph has a unique proteome that could represent a source of valuable biomarkers. Therefore, the aims of this study were to separate and identify the most abundant proteins in the hemolymph of worker honeybees to suggest a panel of these proteins that could represent useful biomarkers for assessing the nutritional and health status of the colonies and, finally, to analyze them in different periods of the year. Four apiaries were selected in the province of Bologna, and the bees were analyzed in April, May, July, and November. Thirty specimens from three hives of each apiary were sampled and their hemolymph was collected. The most represented bands obtained after 1D sodium-dodecyl-sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were cut from the gel, and the proteins were identified using an LC-ESI-Q-MS/MS System. A total of twelve proteins were unmistakably identified; the two most abundant proteins were apolipophorin and vitellogenin, which are known biomarkers of bee trophic and health status. The two other proteins identified were transferrin and hexamerin 70a, the first being involved in iron homeostasis and the second being a storage protein. Most of these proteins showed an increase from April to November, mirroring the physiological changes of honeybees during the productive season. The current study suggests a panel of biomarkers from honeybee hemolymph worth testing under different physiological and pathological field conditions.

Predicted structure of odorant-binding protein 12 from Monochamus alternatus (Hope) suggests a mechanism of flexible odorant-binding

Odorant-binding proteins (OBPs) are thought to bind and deliver hydrophobic odorants from the environment to receptors on insect sensory neurons, and have been used to screen behaviorally active compounds of insects. In order to screen behaviorally active compounds for Monochamus alternatus by OBPs, we cloned full length of Obp12 coding sequence from M. alternatus and proved secretion property of MaltOBP12, then tested binding affinities of recombinant MaltOBP12 to 12 pine volatiles in vitro. We confirmed MaltOBP12 has binding affinities to 9 pine volatiles. The structure of MaltOBP12 and protein-ligand interactions were further analyzed by homology modeling, molecular docking, site-directed mutagenesis, and ligand-binding assays. These results demonstrated that the binding pocket of MaltOBP12 consists of several large aromatic and hydrophobic residues, and four aromatic residues (Tyr50, Phe109, Tyr112, Phe122) are essential for odorant-binding; ligands adopt extensive hydrophobic interactions with an overlapping subset of residues in the binding pocket. Finally, based on non-directional hydrophobic interactions, MaltOBP12 binds odorants flexibly. These findings will not only help us understand how OBPs flexibly bind odorants but also promote to screen of behaviourally active compounds by computer methods to prevent M. alternatus in the future.

Expression and functional analysis of an odorant binding protein PopeOBP16 from Phthorimaea operculella (Zeller)

Odorant binding proteins (OBPs) are essential proteins in the peripheral olfactory system, responsible for odorant recognition and transport to olfactory receptors. Phthorimaea operculella (potato tuber moth) is an important oligophagous pest on Solanaceae crops in many countries and regions. PopeOBP16 is one of the OBPs in potato tuber moth. This study examined the expression profiles of PopeOBP16. The results of qPCR indicated that PopeOBP16 was highly expressed in the antennae of adults, especially in males, suggesting that it may be involved in odor recognition in adults. The electroantennogram (EAG) was used to screen candidate compounds with the antennae of P. operculella. The relative affinities of PopeOBP16 to 27 host volatiles and two sex pheromone components with the highest relative EAG responses were examined with competitive fluorescence-based binding assays. PopeOBP16 had the strongest binding affinity with the plant volatiles: nerol, 2-phenylethanol, linalool, 1,8-cineole, benzaldehyde, β-pinene, d-limonene, terpinolene, α-terpinene, and the sex pheromone component trans-4, cis-7, cis-10-tridecatrien-1-ol acetate. The results provide a foundation for further research into the functioning of the olfactory system and the potential development of green chemistry for control of the potato tuber moth.

Chemosensory Coding in Drosophila Single Sensilla

The chemical senses-smell and taste-detect and discriminate an enormous diversity of environmental stimuli and provide fascinating but challenging models to investigate how sensory cues are represented in the brain. Important stimulus-coding events occur in peripheral sensory neurons, which express specific combinations of chemosensory receptors with defined ligand-response profiles. These receptors convert ligand recognition into spatial and temporal patterns of neural activity that are transmitted to, and interpreted in, central brain regions. Drosophila melanogaster provides an attractive model to study chemosensory coding because it possesses relatively simple peripheral olfactory and gustatory systems that display many organizational parallels to those of vertebrates. Moreover, nearly all peripheral chemosensory neurons have been molecularly characterized and are accessible for physiological analysis, as they are exposed on the surface of sensory organs housed in specialized hairs called sensilla. Here, we briefly review anatomical, molecular, and physiological properties of adult Drosophila olfactory and gustatory systems and provide background to methods for electrophysiological recordings of ligand-evoked activity from different types of chemosensory sensilla.

Pleiotropic fitness effects of a Drosophila odorant-binding protein

Insect odorant-binding proteins (OBPs) are members of a rapidly evolving multigene family traditionally thought to facilitate chemosensation. However, studies on Drosophila have shown that members of this family have evolved functions beyond chemosensation, as evident from their expression in reproductive tissues and the brain. Previous studies implicated diverse functions of Obp56h, a member of the largest gene cluster of the D. melanogaster Obp repertoire. Here, we examined the effect of CRISPR/Cas9-mediated deletion of Obp56h on 2 fitness phenotypes, on resistance to starvation stress and heat stress, and on locomotion and sleep phenotypes. Obp56h-/- mutants show a strong sexually dimorphic effect on starvation stress survival, with females being more resistant to starvation stress than the control. In contrast, Obp56h-/- females, but not males, are highly sensitive to heat stress. Both sexes show changes in locomotion and sleep patterns. Transcriptional profiling of RNA from heads of Obp56h-/- flies and the wildtype control reveals differentially expressed genes, including gene products associated with antimicrobial immune responses and members of the Turandot family of stress-induced secreted peptides. In addition, differentially expressed genes of unknown function were identified in both sexes. Genes encoding components of the mitochondrial electron transport chain, cuticular proteins, gene products associated with regulation of feeding behavior (Lst and CCHa2), ribosomal proteins, lncRNAs, snoRNAs, tRNAs, and snRNAs show changes in transcript abundances in Obp56h-/- females. These differentially expressed genes are likely to contribute to Obp56h-mediated effects on the diverse phenotypes that arise upon deletion of this OBP.

A Highly Expressed Antennae Odorant-Binding Protein Involved in Recognition of Herbivore-Induced Plant Volatiles in Dastarcus helophoroides

Natural enemies such as parasitoids and parasites depend on sensitive olfactory to search for their specific hosts. Herbivore-induced plant volatiles (HIPVs) are vital components in providing host information for many natural enemies of herbivores. However, the olfactory-related proteins involved in the recognition of HIPVs are rarely reported. In this study, we established an exhaustive tissue and developmental expression profile of odorant-binding proteins (OBPs) from Dastarcus helophoroides, an essential natural enemy in the forestry ecosystem. Twenty DhelOBPs displayed various expression patterns in different organs and adult physiological states, suggesting a potential involvement in olfactory perception. In silico AlphaFold2-based modeling and molecular docking showed similar binding energies between six DhelOBPs (DhelOBP4, 5, 6, 14, 18, and 20) and HIPVs from Pinus massoniana. While in vitro fluorescence competitive binding assays showed only recombinant DhelOBP4, the most highly expressed in the antennae of emerging adults could bind to HIPVs with high binding affinities. RNAi-mediated behavioral assays indicated that DhelOBP4 was an essential functional protein for D. helophoroides adults recognizing two behaviorally attractive substances: p-cymene and γ-terpinene. Further binding conformation analyses revealed that Phe 54, Val 56, and Phe 71 might be the key binding sites for DhelOBP4 interacting with HIPVs. In conclusion, our results provide an essential molecular basis for the olfactory perception of D. helophoroides and reliable evidence for recognizing the HIPVs of natural enemies from insect OBPs' perspective.

The seminal odorant binding protein Obp56g is required for mating plug formation and male fertility in Drosophila melanogaster

In Drosophila melanogaster and other insects, the seminal fluid proteins (SFPs) and male sex pheromones that enter the female with sperm during mating are essential for fertility and induce profound post-mating effects on female physiology and behavior. The SFPs in D. melanogaster and other taxa include several members of the large gene family known as odorant binding proteins (Obps). Previous work in Drosophila has shown that some Obp genes are highly expressed in the antennae and can mediate behavioral responses to odorants, potentially by binding and carrying these molecules to odorant receptors. These observations have led to the hypothesis that the seminal Obps might act as molecular carriers for pheromones or other compounds important for male fertility in the ejaculate, though functional evidence in any species is lacking. Here, we used RNAi and CRISPR/Cas9 generated mutants to test the role of the seven seminal Obps in D. melanogaster fertility and the post-mating response (PMR). We found that Obp56g is required for male fertility and the induction of the PMR, whereas the other six genes had no effect on fertility when mutated individually. Obp56g is expressed in the male's ejaculatory bulb, an important tissue in the reproductive tract that synthesizes components of the mating plug. We found males lacking Obp56g fail to form a mating plug in the mated female's reproductive tract, leading to ejaculate loss and reduced sperm storage. We also examined the evolutionary history of these seminal Obp genes, as several studies have documented rapid evolution and turnover of SFP genes across taxa. We found extensive lability in gene copy number and evidence of positive selection acting on two genes, Obp22a and Obp51a. Comparative RNAseq data from the male reproductive tract of multiple Drosophila species revealed that Obp56g shows high male reproductive tract expression only in species of the melanogaster and obscura groups, though conserved head expression in all species tested. Together, these functional and expression data suggest that Obp56g may have been co-opted for a reproductive function over evolutionary time.

Conserved Odorant Receptor, EcorOR4, Mediates Attraction of Mated Female Eupeodes corollae to 1-Octen-3-ol

Odorant receptors (ORs) in insects are crucial for the detection of chemical signals. However, the functions of the conserved OR genes among insect species are rarely studied. In this study, we analyzed a well-conserved OR clade in Diptera insects and cloned a gene from this clade, EcorOR4, in the hoverfly Eupeodes corollae. Real-time quantitative PCR showed that EcorOR4 was highly expressed in the antennae and upregulated in the mated females, and in vitro functional characterization showed that EcorOR4 was narrowly tuned to 1-octen-3-ol. Electroantennogram assays revealed that the antennal response of mated females to 1-octen-3-ol was significantly higher than that of mated males, but no significant differences were observed between male and female virgins. Finally, a Y-tube olfactometer bioassay showed that 1-octen-3-ol is an attractant for only mated female E. corollae adults. These results demonstrate that EcorOR4 is involved in the detection of 1-octen-3-ol and that this compound may affect the host-finding and oviposition behavior in female E. corollae.

Proteinaceous Venom Expression of the Yellow Meadow Ant, Lasius flavus (Hymenoptera: Formicidae)

Ants are one of the important groups of venomous animals with about 14,000 described species. Studies so far focused on the discovery of venom proteins are only available for limited stinging ants, and the proteinaceous compositions of the stingless ants are completely unknown. Here, we used the transcriptomic approach to identify venom components from the yellow meadow ant, Lasius flavus, a stingless ant. The transcriptomic analysis yielded an extraordinary simplicity of the venom expression profile, with 17 venom proteins, such as phospholipase B, odorant binding protein, and apolipoprotein D. Ten of them were discovered as novel toxins for future functional investigations. Quantitative real time PCR analysis revealed that genes encoding the identified venom proteins display exclusively or highly expression profiles in venom glands, validating them as venom compositions. Our findings contribute to the understanding of the evolutional diversity of toxins between stinging and stingless ants.

A draft Diabrotica virgifera virgifera genome: insights into control and host plant adaption by a major maize pest insect

BACKGROUND

Adaptations by arthropod pests to host plant defenses of crops determine their impacts on agricultural production. The larval host range of western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), is restricted to maize and a few grasses. Resistance of D. v. virgifera to crop rotation practices and multiple insecticides contributes to its status as the most damaging pest of cultivated maize in North America and Europe. The extent to which adaptations by this pest contributes to host plant specialization remains unknown.

RESULTS

A 2.42 Gb draft D. v. virgifera genome, Dvir_v2.0, was assembled from short shotgun reads and scaffolded using long-insert mate-pair, transcriptome and linked read data. K-mer analysis predicted a repeat content of ≥ 61.5%. Ortholog assignments for Dvir_2.0 RefSeq models predict a greater number of species-specific gene duplications, including expansions in ATP binding cassette transporter and chemosensory gene families, than in other Coleoptera. A majority of annotated D. v. virgifera cytochrome P450s belong to CYP4, 6, and 9 clades. A total of 5,404 transcripts were differentially-expressed between D. v. virgifera larvae fed maize roots compared to alternative host (Miscanthus), a marginal host (Panicum virgatum), a poor host (Sorghum bicolor) and starvation treatments; Among differentially-expressed transcripts, 1,908 were shared across treatments and the least number were between Miscanthus compared to maize. Differentially-expressed transcripts were enriched for putative spliceosome, proteosome, and intracellular transport functions. General stress pathway functions were unique and enriched among up-regulated transcripts in marginal host, poor host, and starvation responses compared to responses on primary (maize) and alternate hosts.

CONCLUSIONS

Manual annotation of D. v. virgifera Dvir_2.0 RefSeq models predicted expansion of paralogs with gene families putatively involved in insecticide resistance and chemosensory perception. Our study also suggests that adaptations of D. v. virgifera larvae to feeding on an alternate host plant invoke fewer transcriptional changes compared to marginal or poor hosts. The shared up-regulation of stress response pathways between marginal host and poor host, and starvation treatments may reflect nutrient deprivation. This study provides insight into transcriptomic responses of larval feeding on different host plants and resources for genomic research on this economically significant pest of maize.

An Overview of D7 Protein Structure and Physiological Roles in Blood-Feeding Nematocera

Each time an insect bites a vertebrate host, skin and vascular injury caused by piercing triggers a series of responses including hemostasis, inflammation and immunity. In place, this set of redundant and interconnected responses would ultimately cause blood coagulation, itching and pain leading to host awareness, resulting in feeding interruption in the best-case scenario. Nevertheless, hematophagous arthropod saliva contains a complex cocktail of molecules that are crucial to the success of blood-feeding. Among important protein families described so far in the saliva of blood sucking arthropods, is the D7, abundantly expressed in blood feeding Nematocera. D7 proteins are distantly related to insect Odorant-Binding Proteins (OBP), and despite low sequence identity, observation of structural similarity led to the suggestion that like OBPs, they should bind/sequester small hydrophobic compounds. Members belonging to this family are divided in short forms and long forms, containing one or two OBP-like domains, respectively. Here, we provide a review of D7 proteins structure and function, discussing how gene duplication and some modifications in their OBP-like domains during the course of evolution lead to gain and loss of function among different hematophagous Diptera species.

Drosophila olfaction: past, present and future

Among the many wonders of nature, the sense of smell of the fly Drosophila melanogaster might seem, at first glance, of esoteric interest. Nevertheless, for over a century, the 'nose' of this insect has been an extraordinary system to explore questions in animal behaviour, ecology and evolution, neuroscience, physiology and molecular genetics. The insights gained are relevant for our understanding of the sensory biology of vertebrates, including humans, and other insect species, encompassing those detrimental to human health. Here, I present an overview of our current knowledge of D. melanogaster olfaction, from molecules to behaviours, with an emphasis on the historical motivations of studies and illustration of how technical innovations have enabled advances. I also highlight some of the pressing and long-term questions.

Pheromone sensing in Drosophila requires support cell-expressed Osiris 8

Background

The nose of most animals comprises multiple sensory subsystems, which are defined by the expression of different olfactory receptor families. Drosophila melanogaster antennae contain two morphologically and functionally distinct subsystems that express odorant receptors (Ors) or ionotropic receptors (Irs). Although these receptors have been thoroughly characterized in this species, the subsystem-specific expression and roles of other genes are much less well-understood.

Results

Here we generate subsystem-specific transcriptomic datasets to identify hundreds of genes, encoding diverse protein classes, that are selectively enriched in either Or or Ir subsystems. Using single-cell antennal transcriptomic data and RNA in situ hybridization, we find that most neuronal genes—other than sensory receptor genes—are broadly expressed within the subsystems. By contrast, we identify many non-neuronal genes that exhibit highly selective expression, revealing substantial molecular heterogeneity in the non-neuronal cellular components of the olfactory subsystems. We characterize one Or subsystem-specific non-neuronal molecule, Osiris 8 (Osi8), a conserved member of a large, insect-specific family of transmembrane proteins. Osi8 is expressed in the membranes of tormogen support cells of pheromone-sensing trichoid sensilla. Loss of Osi8 does not have obvious impact on trichoid sensillar development or basal neuronal activity, but abolishes high sensitivity responses to pheromone ligands.

Conclusions

This work identifies a new protein required for insect pheromone detection, emphasizes the importance of support cells in neuronal sensory functions, and provides a resource for future characterization of other olfactory subsystem-specific genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01425-w.

Proteomic analysis of pharate pupal molting fluid from the tobacco hornworm, Manduca sexta

The insect cuticle is a key component of their success, being important for protection, communication, locomotion, and support. Conversely, as an exoskeleton, it also limits the size of the insect and must be periodically molted and a new one synthesized, to permit growth. To achieve this, the insect secretes a solution of chitinases, proteases and other proteins, known collectively as molting fluid, during each molting process to break down and recycle components of the old cuticle. Previous research has focused on the degradative enzymes in molting fluid and offered some characterization of their biochemical properties. However, identification of the specific proteins involved remained to be determined. We have used 2D SDS-PAGE and LC/MS-based proteomic analysis to identify proteins in the molting fluid of the tobacco hornworm, Manduca sexta, undergoing the larval to pupal molt. We categorized these proteins based on their proposed functions including chitin metabolism, proteases, peptidases, and immunity. This analysis complements previous reported work on M. sexta molting fluid and identifies candidate genes for enzymes involved in cuticle remodeling. Proteins classified as having an immune function highlight potential for molting fluid to act as an immune barrier to prevent infections during the cuticle degradation and ecdysis processes. Several proteins known to function in melanin synthesis as an immune response in hemolymph were present in molting fluid. We demonstrated that the bacterium Micrococcus luteus and the entomopathogenic fungus Beauveria bassiana can stimulate activation of phenoloxidase in molting fluid, indicating that the recognition proteins, protease cascade, and prophenoloxidase needed for melanin synthesis are present as a defense against infection during cuticle degradation. This analysis offers insights for proteins that may be important not only for molting in M. sexta but for insects in general.

Identification of Candidate Chemosensory Gene Families by Head Transcriptomes Analysis in the Mexican Fruit Fly, Anastrepha ludens Loew (Diptera: Tephritidae)

Insect chemosensory systems, such as smell and taste, are mediated by chemosensory receptor and non-receptor protein families. In the last decade, many studies have focused on discovering these families in Tephritidae species of agricultural importance. However, to date, there is no information on the Mexican fruit fly Anastrepha ludens Loew, a priority pest of quarantine importance in Mexico and other countries. This work represents the first effort to identify, classify and characterize the six chemosensory gene families by analyzing two head transcriptomes of sexually immature and mature adults of A. ludens from laboratory-reared and wild populations, respectively. We identified 120 chemosensory genes encoding 31 Odorant-Binding Proteins (OBPs), 5 Chemosensory Proteins (CSPs), 2 Sensory Neuron Membrane Proteins (SNMPs), 42 Odorant Receptors (ORs), 17 Ionotropic Receptors (IRs), and 23 Gustatory Receptors (GRs). The 120 described chemosensory proteins of the Mexican fruit fly significantly contribute to the genetic databases of insects, particularly dipterans. Except for some OBPs, this work reports for the first time the repertoire of olfactory proteins for one species of the genus Anastrepha, which provides a further basis for studying the olfactory system in the family Tephritidae, one of the most important for its economic and social impact worldwide.

EsigGOBP1: The Key Protein Binding Alpha-Phellandrene in Endoclita signifer Larvae

Endoclita signifer larvae show olfactory recognition towards volatiles of eucalyptus trunks and humus soils. Further, EsigGOBP1 was identified through larval head transcriptome and speculated as the main odorant-binding proteins in E. signifer larvae. In this study, the highest expression of EsigGOBP1 was only expressed in the heads of 3rd instar larvae of E. signifer, compared with the thorax and abdomen; this was consistent with the phenomenon of habitat transfer of 3rd instar larvae, indicating that EsigGOBP1 was a key OBP gene in E. signifer larvae. Results of fluorescence competition binding assays (FCBA) showed that EsigGOBP1 had high binding affinities to eight GC-EAD active ligands. Furthermore, screening of key active odorants for EsigGOBP1 and molecular docking analysis, indicated that EsigGOBP1 showed high binding activity to alpha-phellandrene in 3rd instar larvae of E. signifer. Conformational analysis of the EsigGOBP1-alpha-phellandrene complex, showed that MET49 and GLU38 were the key sites involved in binding. These results demonstrated that EsigGOBP1 is a key odorant-binding protein in E. signifer larvae, which recognizes and transports eight key volatiles from eucalyptus trunk, especially the main eucalyptus trunks volatile, alpha-phellandrene. Taken together, our results showed that EsigGOBP1 is involved in host selection of E. signifer larvae, which would aid in developing EsigGOBP1 as molecular targets for controlling pests at the larval stage.

Key Residues Affecting Binding Affinity of Sirex noctilio Fabricius Odorant-Binding Protein (SnocOBP9) to Aggregation Pheromone

Sirex noctilio Fabricius (Hymenoptera Siricidae) is a major quarantine pest responsible for substantial economic losses in the pine industry. To achieve better pest control, (Z)-3-decen-ol was identified as the male pheromone and used as a field chemical trapping agent. However, the interactions between odorant-binding proteins (OBPs) and pheromones are poorly described. In this study, SnocOBP9 had a higher binding affinity with Z3D (Ki = 1.53 ± 0.09 μM) than other chemical ligands. Molecular dynamics simulation and binding mode analysis revealed that several nonpolar residues were the main drivers for hydrophobic interactions between SnocOBP9 and Z3D. Additionally, computational alanine scanning results indicated that five amino acids (MET54, PHE57, PHE71, PHE74, LEU116) in SnocOBP9 could potentially alter the binding affinity to Z3D. Finally, we used single-site-directed mutagenesis to substitute these five residues with alanine. These results imply that the five residues play crucial roles in the SnocOBP9-Z3D complex. Our research confirmed the function of SnocOBP9, uncovered the key residues involved in SnocOBP9-Z3D interactions, and provides an inspiration to improve the effects of pheromone agent traps.

Odorant Binding Proteins (OBPs) and Odorant Receptors (ORs) of Anopheles stephensi: Identification and comparative insights

Anopheles stephensi is an important vector of malaria in the South Asia, the Middle East, and Eastern Africa. The olfactory system of An. stephensi plays an important role in host-seeking, oviposition, and feeding. Odorant binding proteins (OBPs) are globular proteins that play a pivotal role in insect olfaction by transporting semiochemicals through the sensillum lymph to odorant receptors (ORs). Custom motifs designed from annotated OBPs of Aedes aegypti, Drosophila melanogaster, and Anopheles gambiae were used for the identification of putative OBPs from protein sequences of the An. stephensi Indian strain. Further, BLASTp was also performed to identify missing OBPs and ORs. Subsequently, the presence of domains common to OBPs was confirmed. Identified OBPs were further classified into three sub-classes. Phylogenetic and syntenic analyses were carried out to find homology, and thus the evolutionary relationship between An. stephensi OBPs and ORs with those of An. gambiae, Ae. aegypti and D. melanogaster. Gene structure and physicochemical properties of the OBPs and ORs were also predicted. A total of 44 OBPs and 45 ORs were predicted from the protein sequences of An. stephensi. OBPs were further classified into the classic (27), atypical (10) and plus-C (7) OBP subclasses. The phylogeny revealed close relationship of An. stephensi OBPs and ORs with An. gambiae homologs whereas only five OBPs and two ORs of An. stephensi were related to Ae. aegypti OBPs and ORs, respectively. However, D. melanogaster OBPs and ORs were distantly rooted. Synteny analyses showed the presence of collinear block between the OBPs and ORs of An. stephensi and An. gambiae as well as Ae. aegypti’s. No homology was found with D. melanogaster OBPs and ORs. As an important component of the olfactory system, correctly identifying a species’ OBPs and ORs provide a valuable resource for downstream translational research that will ultimately aim to better control the malaria vector An. stephensi.

Photoperiod-Dependent Expression of MicroRNA in Drosophila

Like many other insects in temperate regions, Drosophila melanogaster exploits the photoperiod shortening that occurs during the autumn as an important cue to trigger a seasonal response. Flies survive the winter by entering a state of reproductive arrest (diapause), which drives the relocation of resources from reproduction to survival. Here, we profiled the expression of microRNA (miRNA) in long and short photoperiods and identified seven differentially expressed miRNAs (dme-mir-2b, dme-mir-11, dme-mir-34, dme-mir-274, dme-mir-184, dme-mir-184*, and dme-mir-285). Misexpression of dme-mir-2b, dme-mir-184, and dme-mir-274 in pigment-dispersing, factor-expressing neurons largely disrupted the normal photoperiodic response, suggesting that these miRNAs play functional roles in photoperiodic timing. We also analyzed the targets of photoperiodic miRNA by both computational predication and by Argonaute-1-mediated immunoprecipitation of long- and short-day RNA samples. Together with global transcriptome profiling, our results expand existing data on other Drosophila species, identifying genes and pathways that are differentially regulated in different photoperiods and reproductive status. Our data suggest that post-transcriptional regulation by miRNA is an important facet of photoperiodic timing.

Odorant Binding Protein C17 Contributes to the Response to Artemisia vulgaris Oil in Tribolium castaneum

The red flour beetle, Tribolium castaneum (T. castaneum), generates great financial losses to the grain storage and food processing industries. Previous studies have shown that essential oil (EO) from Artemisia vulgaris (A. vulgaris) has strong contact toxicity to larvae of the beetle, and odorant-binding proteins (OBPs) contribute to the defense of larvae against A. vulgaris. However, the functions of OBPs in insects defending against plant oil is still not clear. Here, expression of one OBP gene, TcOBPC17, was significantly induced 12–72 h after EO exposure. Furthermore, compared to the control group, RNA interference (RNAi) against TcOBPC17 resulted in a higher mortality rate after EO treatment, which suggests that TcOBPC17 involves in the defense against EO and induces a declining sensitivity to EO. In addition, the tissue expression profile analysis revealed that the expression of TcOBPC17 was more abundant in the metabolic detoxification organs of the head, fat body, epidermis, and hemolymph than in other larval tissue. The expression profile of developmental stages showed that TcOBPC17 had a higher level in early and late adult stages than in other developmental stages. Taken together, these results suggest that TcOBPC17 could participate in the sequestration process of exogenous toxicants in T. castaneum larvae.

Time-Dependent Odorant Sensitivity Modulation in Insects

Simple Summary

Insects, including blood-feeding female mosquitoes, can transmit deadly diseases, such as malaria, encephalitis, dengue, and yellow fever. Insects use olfaction to locate food sources, mates, and hosts. The nature of odorant plumes poses a challenge for insects in locating odorant sources in the environment. In order to modulate the system for the detection of fresh stimuli or changes in odorant concentrations, the olfaction system desensitizes to different concentrations and durations of stimuli. Without this ability, the chemotaxis behaviors of insects are defective. Thus, understanding how insects adjust their olfactory response dynamics to parse the chemical language of the external environment is not only a basic biology question but also has far-reaching implications for repellents and pest control.

Abstract

Insects use olfaction to detect ecologically relevant chemicals in their environment. To maintain useful responses over a variety of stimuli, olfactory receptor neurons are desensitized to prolonged or high concentrations of stimuli. Depending on the timescale, the desensitization is classified as short-term, which typically spans a few seconds; or long-term, which spans from minutes to hours. Compared with the well-studied mechanisms of desensitization in vertebrate olfactory neurons, the mechanisms underlying invertebrate olfactory sensitivity regulation remain poorly understood. Recently, using a large-scale functional screen, a conserved critical receptor phosphorylation site has been identified in the model insect Drosophila melanogaster, providing new insight into the molecular basis of desensitization in insects. Here, we summarize the progress in this area and provide perspectives on future directions to determine the molecular mechanisms that orchestrate the desensitization in insect olfaction.

Perspectives on Odor-Based Control of Tsetse Flies in Africa

Tsetse-transmitted trypanosomiases are among the most neglected tropical diseases in sub-Sahara Africa. Although all tsetse species are susceptible to trypanosome infections, their differential attraction/feeding preferences for different wildlife, domestic animals, and/or humans constitute critical determinants of trypanosomes species they predominantly transmit. Artificial bait technologies, based on long-range tsetse olfactory responses to natural cues emitted by preferred hosts and blends of synthetic versions that mimic these cues, have successfully been applied in attractant-odor-based (“pull” tactic) reduction of field populations of some tsetse species. Olfactory attribute associated with active avoidance of tsetse-refractory non-hosts has similarly been exploited in design of repellent-odor-based (“push” tactic) protection of livestock. These tactics have opened possibility of spatially strategic deployment of the two sets of odor baits in “push-pull” tactics. Possibility of developing blends with enhanced attraction and repellence compared with those associated with savannah tsetse fly hosts and non-hosts, respectively, have been explored, where structure activity and blends of different components generated two novel blends. The studies evaluated structure activity and blends of different components. One based on attractive constituents associated with buffalo (Syncerus caffer) comprised of ε-nonalactone, nonanoic acid, 2-nonanone (in 1:3:2 proportion) delivered together with acetone, which showed significantly better attractancy on savannah tsetse fly than the standard blend comprised of 3-propylphenol, octenol, p-cresol, and acetone (POCA). The other blend comprised of δ-nonalactone, heptanoic acid, 4-methylguaiacol and geranylacetone (in 6:4:2:1 proportion) was significantly more repellent than previously characterized blend based on tsetse fly refractory waterbuck (Kobus defassa) constituents (δ-octalactone, pentanoic acid, guaiacol and geranylacetone). So far, no effective attractants or repellents of riverine tsetse fly species have been characterized. Optimized attractant and repellent blends for savannah tsetse flies lay down useful groundwork for future development of the “push-pull” deployment tactic for area-wide control of tsetse flies. Better understanding of the physiological, cellular, and molecular basis of response in the tsetse fly to odors can potentially augment the current tsetse fly-control interventions.