Gustatory Receptors Research Articles

Chemosensory function of Varroa gnathosoma: transcriptomic and proteomic analyses

In this study, we evaluated the role of the gnathosoma (mouthparts) in chemosensing of the most devastating honey bee parasite, Varroa destructor mite. Through transcriptomic analysis, we compared the expression of putative chemosensory genes between the body parts containing the main chemosensory organs (the forelegs), gnathosoma and the rest of the body devoid of these two body parts. Furthermore, we checked the presence of chemosensory-related transcripts in the proteome of the gnathosoma. Our comparative transcriptomic analysis revealed the presence of 83 transcripts with known characteristic conserved domains belonging to eight chemosensory gene families in the three Varroa transcriptomes. Among these transcripts, 11 were significantly upregulated in the mite’s forelegs, compared to 8 and 10 in the gnathosoma and body devoid of both organs, respectively. Whilst the gnathosoma and the forelegs share similar expression of some putative lipid carrier proteins, membrane-bound receptors, and associated proteins, they also differ in the expression profiles of some transcripts belonging to these protein families. This suggests two functional chemosensory organs that may differ in their chemosensory function according to specific characteristics of compounds they detect. Moreover, the higher expression of some chemosensory transcripts in the body devoid of forelegs and gnathosoma compared to the gnathosoma alone, may suggest the presence of additional function of these transcripts or alternatively presence of additional external or internal chemosensory organs. Insights into the functional annotation of a highly expressed gustatory receptor present in both organs using RNA interference (RNAi) are also revealed.

The gustatory receptor BdorGr43a mediated sucrose preference in the feeding of Bactrocera dorsalis

The feeding behavior of animals is pivotal for their reproductive success and energy acquisition. In our study, we found that the Bactrocera dorsalis had a pronounced preference for sucrose among six plant-derived sugars during feeding. Then, we searched the entire genome of B. dorsalis for the gustatory receptors (Grs) responsible for sucrose sensation. Putative gustatory receptors involved in the detection of sweetness, bitterness, CO2 and other unknown functions. Together with phylogenetic analysis, expression profiling, calcium imaging, and CRISPR/Cas9 mediated mutagenesis, we found that BdorGr43a is the key receptor responding to sucrose. Our study elucidated the molecular mechanism underlying the sucrose preferences in the feeding of B. dorsalis. Meanwhile, our results will serve as a reference for the understanding of gustatory sensing in insect. Furthermore, BdorGr43a may serve as an important target for the development of food attractants against the oriental fruit fly.

Olfactory and gustatory chemical sensor systems in the African turquoise killifish: Insights from morphology

Smell and taste are extensively studied in fish species as essential for finding food and selecting mates while avoiding toxic substances and predators. Depending on the evolutionary position and adaptation, a discrete variation in the morphology of these sense organs has been reported in numerous teleost species. Here, for the first time, we approach the phenotypic characterization of the olfactory epithelium and taste buds in the African turquoise killifish (Nothobranchius furzeri), a model organism known for its short lifespan and use in ageing research. Our observations indicate that the olfactory epithelium of N. furzeri is organized as a simple patch, lacking the complex folding into a rosette, with an average size of approximately 600 µm in length, 300 µm in width, and 70 µm in thickness. Three main cytotypes, including olfactory receptor neurons (CalbindinD28K), supporting cells (β-tubulin IV), and basal cells (Ki67), were identified across the epithelium. Further, we determined the taste buds’ distribution and quantification between anterior (skin, lips, oral cavity) and posterior (gills, pharynx, oesophagus) systems. We identified the key cytotypes by using immunohistochemical markers, i.e. CalbindinD28K, doublecortin, and neuropeptide Y (NPY) for gustatory receptor cells, glial fibrillary acidic protein (GFAP) for supporting cells, and Ki67, a marker of cellular proliferation for basal cells. Altogether, these results indicate that N. furzeri is a microsmatic species with unique taste and olfactory features and possesses a well-developed posterior taste system compared to the anterior. This study provides fundamental insights into the chemosensory biology of N. furzeri, facilitating future investigations into nutrient-sensing mechanisms and their roles in development, survival, and ageing.

Age-dependent switched taste behavior to ribose

Chemical detection is vital for animal survival, aiding in avoiding toxins and selecting nutritious foods. While Drosophila larvae exhibit appetitive feeding behavior toward ribose, an important sugar for RNA, nucleotide, and nucleoside synthesis, how adult Drosophila perceives ribose remains unclear. Through behavioral and electrophysiological investigations, we unexpectedly discovered that adult flies actively avoid ribose. Our external electrophysiological analysis revealed that ribose is detected through bitter-sensing gustatory receptor neurons in S-type sensilla, suggesting its perception as a bitter compound. Additionally, we identify painless as crucial for both ribose aversion and the neuronal response to ribose.

Advanced investigation of adsorption process of the five main responses of taste molecules onto the gerbil receptor sites (GCaMP3): Steric, molecular docking, and energy interpretations

In this research work, an adsorption phenomenon putatively in the process of taste at a molecular level for understanding the five principal tastes using experimental dose-gustatory responses on receptors sites of gerbil (GCaMP3). In order to perform theoretical interpretations of the experimental data of dose gustatory response curve were fitted with the single-layer physical model (PMM) for sucrose, cycloheximide, quinine and MSG. However, a two-layer with two-energies model for NaCl and citric acid. The modeling discussion indicated that all six molecules were linked with the gerbil receptor sites of tasting surface by a parallel and a no parallel orientations. In addition, the linking adsorption energies are ranged from 3.15 to 14.19 kJ/mol for all tasting molecules, which suggested that this process is performed by a reversible physical adsorption. These physico-chemical model parameters are utilized to determine the molar energy of adsorption for various taste-entities. By fitting the number of adsorbed molecules or molecular anchors per site, a stereographic and energetic characterization of interactions between six entities (sucrose, cycloheximide, MSG, citric acid, and NaCl) and the gerbil gustatory-receptor-sites is conducted. These distributions AED and PSD can be considered as a characterization of taste of not only not only not only of any gustatory entity but also a characterization of the gustatory receptor systems of the peripheric nerves. The docking computation between five gustatory molecules and the gerbil GCaMP3 cavity receptor sites is performed, showing a significant resemblance in the receptor-ligand detection process. Hence, the findings from docking confirm that the calculated binding affinities fell within the range of adsorption energies.

A Neuropeptide Signaling Network That Regulates Developmental Timing and Systemic Growth in Drosophila.

Animals sense chemical cues such as nutritious and noxious stimuli through the chemosensory system and adapt their behavior, physiology, and developmental schedule to the environment. In the Drosophila central nervous system, chemosensory interneurons that produce neuropeptides called Hugin (Hug) peptides receive signals from gustatory receptor neurons and regulate feeding behavior. Because Hug neurons project their axons to the higher brain region within the protocerebrum where dendrites of multiple neurons producing developmentally important neuropeptides are extended, it has been postulated that Hug neurons regulate development through the neuroendocrine system. In this study, we show that Hug neurons interact with a subset of protocerebrum neurons that produce prothoracicotropic hormone (PTTH) and regulate the onset of metamorphosis and systemic growth. Loss of the hug gene and silencing of Hug neurons caused a delay in larval-to-prepupal transition and an increase in final body size. Furthermore, deletion of Hug receptor-encoding genes also caused developmental delay and body size increase, and the phenotype was restored by expressing Hug receptors in PTTH-producing neurons. These results indicate that Hug neurons regulate developmental timing and body size via PTTH-producing neurons. This study provides a basis for understanding how chemosensation is converted into neuroendocrine signaling to control insect growth and development.

Molecular Functions and Physiological Roles of Gustatory Receptors of the Silkworm Bombyx mori.

Complete elucidation of members of the gustatory receptor (Gr) family in lepidopteran insects began in the silkworm Bombyx mori. Grs of lepidopteran insects were initially classified into four subfamilies based on the results of phylogenetic studies and analyses of a few ligands. However, with further ligand analysis, it has become clear that plant secondary metabolites are important targets not only for Grs in the bitter subfamily but also for the Drosophila melanogaster Gr43a orthologue subfamily and Grs in the sugar subfamily. Gene knockout experiments showed that B. mori Gr6 (BmGr6) and BmGr9 are involved in the recognition of the feeding-promoting compounds chlorogenic acid and isoquercetin in mulberry leaves by the maxillary palps, suggesting that these Grs are responsible for palpation-dependent host recognition without biting. On the other hand, BmGr expression was also confirmed in nonsensory organs. Midgut enteroendocrine cells that produce specific neuropeptides were shown to express specific BmGrs, suggesting that BmGrs are involved in the induction of endocrine secretion in response to changes in the midgut contents. Furthermore, gene knockout experiments indicated that BmGr6 is indeed involved in the secretion of myosuppressin. On the other hand, BmGr9 was shown to induce signal transduction that is not derived from the intracellular signaling cascade mediated by G proteins but from the fructose-regulated cation channel of BmGr9 itself. Cryogenic electron microscopy revealed the mechanism by which the ion channel of the BmGr9 homotetramer opens upon binding of fructose to the ligand-binding pocket. Research on BmGrs has contributed greatly to our understanding of the functions and roles of Grs in insects.

Antennal Transcriptome Screening and Identification of Chemosensory Proteins in the Double-Spine European Spruce Bark Beetle, Ips duplicatus (Coleoptera: Scolytinae).

The northern bark beetle, Ips duplicatus, is an emerging economic pest, reportedly infesting various species of spruce (Picea spp.), pine (Pinus spp.), and larch (Larix spp.) in Central Europe. Recent climate changes and inconsistent forest management practices have led to the rapid spread of this species, leaving the current monitoring strategies inefficient. As understanding the molecular components of pheromone detection is key to developing novel control strategies, we generated antennal transcriptomes from males and females of this species and annotated the chemosensory proteins. We identified putative candidates for 69 odorant receptors (ORs), 50 ionotropic receptors (IRs), 25 gustatory receptors (GRs), 27 odorant-binding proteins (OBPs), including a tetramer-OBP, 9 chemosensory proteins (CSPs), and 6 sensory neuron membrane proteins (SNMPs). However, no sex-specific chemosensory genes were detected. The phylogenetic analysis revealed conserved orthology in bark beetle chemosensory proteins, especially with a major forest pest and co-habitant, Ips typographus. Recent large-scale functional studies in I. typographus chemoreceptors add greater significance to the orthologous sequences reported here. Nevertheless, identifying chemosensory genes in I. duplicatus is valuable to understanding the chemosensory system and its evolution in bark beetles (Coleoptera) and, generally, insects.

Functional and evolutionary insights into chemosensation and specialized herbivory from the genome of the red milkweed beetle, Tetraopes tetrophthalmus (Cerambycidae: Lamiinae).

Tetraopes are aposematic longhorn beetles (Cerambycidae) that feed primarily on toxic plants in the genus Asclepias (milkweeds). Studies of Tetraopes and their host plants have revealed compelling evidence for insect-plant coevolution and cospeciation. We sequenced, assembled and annotated the genome of the common red milkweed beetle, Tetraopes tetrophthalmus, and explored gene content and evolution, focusing on annotated genes putatively involved in chemosensation, allelochemical detoxification, and phytophagy. Comparisons were made to the Asian longhorned beetle (Anoplophora glabripennis) genome. The genome assembly comprised 779Mb distributed across 1057 contigs, with an N50 of 2.21Mb and 13,089 putative genes, including 97.3% of expected single-copy orthologs. Manual curation identified 122 putative odorant receptors (OR) and 162 gustatory receptors (GR), the former number similar to A. glabripennis but the latter only 69% of the A. glabripennis suite. We also documented a greater percentage of pseudogenic GRs and ORs compared to A. glabripennis, suggesting an ongoing reduction in chemosensory function, perhaps related to host specialization. We found lower diversity within certain well-studied gene families predicted to encode putative plant cell wall degrading enzymes in the T. tetrophthalmus genome, perhaps also due to host specialization. Exploring genes relevant to stress and allelochemical detoxification revealed evidence of an abundance of ABC-family genes in the T. tetrophthalmus genome, which may be related to sequestering toxic cardiac glycosides. Our studies further illuminate the genomic basis and evolution of chemosensation in longhorn beetles and provide a new vantage point from which to explore the ecology and evolution of specialized plant-feeding in Tetraopes and other phytophagous beetles.

Gustatory receptor 11 is involved in detecting the oviposition water of Asian tiger mosquito, Aedes albopictus

BackgroundAedes albopictus is a major arbovirus vector with small stagnant water containers being its oviposition sites. Mosquitoes search for these sites based on their olfactory cues (odor and moisture emanating from the water at the oviposition site), visual cues (size and color of the site), and gustatory cues (ion and nutrient concentration in that water). The gustatory mechanism through which mosquitoes search for oviposition sites remains unknown.MethodsTo investigate the role of taste receptors in Ae. albopictus oviposition site selection, we developed a laboratory model. This model assessed mosquito behavior in locating and detecting oviposition sites, using a location index to quantify site preference and detection time to measure response to water presence. We compared oviposition site-searching efficiency between mosquitoes with blocked and unblocked appendages, targeting the taste organs. Transcriptome sequencing was conducted to identify differentially expressed genes between water-exposed and unexposed mosquitoes. CRISPR/Cas9 technology was then employed to generate a mutant strain with a targeted gene knockout.ResultsThere was no significant difference between the blocked and unblocked groups in the location index. In contrast, the detection time of the unblocked group differed significantly from all other groups, including those with blocked foreleg tarsus, midleg tarsus, hindleg tarsus, all tibia, and all tarsus. Transcriptome sequencing analyses of water-exposed and unexposed mosquitoes revealed that the taste-related gene gustatory receptor 11(gr11) was differentially expressed. This gene was knocked out with CRISPR/Cas9 technology to generate a pure mutant strain with 2- and 4-bp deletions, which exhibited a significantly longer detection time than the wild-type strain.ConclusionsThis study reveals the role of Ae. albopictus gr11 in water detection at oviposition sites, thereby providing a theoretical basis and scientific guidelines for managing the breeding sites of these mosquitoes.Graphical

Sex Differences in Antennal Transcriptome of Hyphantria cunea and Analysis of Odorant Receptor Expression Profiles.

Insects rely on olfaction for mating, finding oviposition sites, and locating hosts. Hyphantria cunea is a serious pest that severely damages forests. Differential expression analysis of olfactory-related genes between males and females is the basis for elucidating the functions of olfactory-related proteins in H. cunea. In this study, Illumina HiSeqTM 4000 high-throughput sequencing technology was used to perform transcriptome sequencing of the antennal tissues of adult male and female H. cunea. Functional annotation was conducted using the NR, Swiss-Prot, KOG, KEGG, and GO databases, and the results showed that the antennal transcriptome of adult H. cunea contained 50,158 unigenes. Differential expression analysis identified 3923 genes that were significantly differentially expressed between male and female antennae. A total of 221 olfactory-related genes were annotated, and 96 sex-biased genes were identified, including 13 odorant receptors (ORs), 48 odorant binding proteins (OBPs), 7 chemosensory proteins (CSPs), 10 ionotropic receptors (IRs), 10 sensory neuron membrane proteins (SNMPs), 2 gustatory receptors (GRs), and 6 odorant-degrading enzymes (ODEs), indicating that there were differences in olfaction between male and female H. cunea. Quantitative real-time PCR was used to verify the expression levels of 21 putative general odorant receptor genes in male and female antennae. HcunOR4 and HcunOR5 showed female-biased expression; HcunOR48, HcunOR49 and HcunOR50 showed male-biased expression. The results were consistent with the transcriptome differential analysis. The screening of male-biased odorant receptor genes might provide a theoretical basis for the functional characterization of odorant receptors for recognizing sex pheromones in H. cunea.

Few chemoreceptor genes in the ambrosia beetle Trypodendron lineatum may reflect its specialized ecology

BackgroundChemoreception is crucial for insect fitness, underlying for instance food-, host-, and mate finding. Chemicals in the environment are detected by receptors from three divergent gene families: odorant receptors (ORs), gustatory receptors (GRs), and ionotropic receptors (IRs). However, how the chemoreceptor gene families evolve in parallel with ecological specializations remains poorly understood, especially in the order Coleoptera. Hence, we sequenced the genome and annotated the chemoreceptor genes of the specialised ambrosia beetle Trypodendron lineatum (Coleoptera, Curculionidae, Scolytinae) and compared its chemoreceptor gene repertoires with those of other scolytines with different ecological adaptations, as well as a polyphagous cerambycid species.ResultsWe identified 67 ORs, 38 GRs, and 44 IRs in T. lineatum (‘Tlin’). Across gene families, T. lineatum has fewer chemoreceptors compared to related scolytines, the coffee berry borer Hypothenemus hampei and the mountain pine beetle Dendroctonus ponderosae, and clearly fewer receptors than the polyphagous cerambycid Anoplophora glabripennis. The comparatively low number of chemoreceptors is largely explained by the scarcity of large receptor lineage radiations, especially among the bitter taste GRs and the ‘divergent’ IRs, and the absence of alternatively spliced GR genes. Only one non-fructose sugar receptor was found, suggesting several sugar receptors have been lost. Also, we found no orthologue in the ‘GR215 clade’, which is widely conserved across Coleoptera. Two TlinORs are orthologous to ORs that are functionally conserved across curculionids, responding to 2-phenylethanol (2-PE) and green leaf volatiles (GLVs), respectively.ConclusionsTrypodendron lineatum reproduces inside the xylem of decaying conifers where it feeds on its obligate fungal mutualist Phialophoropsis ferruginea. Like previous studies, our results suggest that stenophagy correlates with small chemoreceptor numbers in wood-boring beetles; indeed, the few GRs may be due to its restricted fungal diet. The presence of TlinORs orthologous to those detecting 2-PE and GLVs in other species suggests these compounds are important for T. lineatum. Future functional studies should test this prediction, and chemoreceptor annotations should be conducted on additional ambrosia beetle species to investigate whether few chemoreceptors is a general trait in this specialized group of beetles.

Identification and expression profiles of olfactory-related genes in the antennal transcriptome of Graphosoma rubrolineatum (Hemiptera: Pentatomidae).

Graphosoma rubrolineatum (Hemiptera: Pentatomidae) is an important pest of vegetables and herbs (e.g., Umbelliferae and Cruciferae) in China, Siberia, Korea, and Japan. Insects are highly dependent on their olfactory system to detect odorants. However, no molecular-mediated olfactory genes in G. rubrolineatum have yet been identified. In this study, we first established the antennal transcriptome of G. rubrolineatum and identified 189 candidate olfactory genes, including 31 odorant-binding proteins (OBPs), 15 chemosensory proteins (CSPs), four sensory neuron membrane proteins (SNMPs),94 odorant receptors (ORs), 23 ionotropic receptors (IRs), and 22 gustatory receptors (GRs). Additionally, phylogenetic trees were constructed for olfactory genes between G. rubrolineatum and other hemipteran insects. We also detected the expression profiles of ten OBPs, five CSPs, two SNMPs, five ORs, four IRs, and four GRs by real-time quantitative PCR. The results revealed that most genes (GrubOBP1/11/31, GrubCSP3/8, GrubSNMP1a/1b, GrubOrco/OR9/11/13, GrubGR1/4/22, GrubIR25/75h/76b/GluR1) were highly expressed in the antennae, GrubOBP13/31 and GrubCSP4/11/12 were highly expressed in the legs, while GrubOBP20 and GrubGR19 were highly expressed in the wings. Our results will enrich the gene inventory of G. rubrolineatum and provide further insight into the molecular chemosensory mechanisms of G. rubrolineatum.

Finding the sweet spot of the insect gustatory receptor

In a recent issue of Nature, Gomes etal.1 utilized structural, experimental, and computational biology to investigate the ligand-gated activation of BmGr9, an insect gustatory receptor specifically tuned to D-fructose. Together with two other studies published elsewhere, they are the first to describe how sugars bind to insect gustatory receptors.

Drosophila HCN mediates gustatory homeostasis by preserving sensillar transepithelial potential in sweet environments.

Establishing transepithelial ion disparities is crucial for sensory functions in animals. In insect sensory organs called sensilla, a transepithelial potential, known as the sensillum potential (SP), arises through active ion transport across accessory cells, sensitizing receptor neurons such as mechanoreceptors and chemoreceptors. Because multiple receptor neurons are often co-housed in a sensillum and share SP, niche-prevalent overstimulation of single sensory neurons can compromise neighboring receptors by depleting SP. However, how such potential depletion is prevented to maintain sensory homeostasis remains unknown. Here, we find that the Ih-encoded hyperpolarization-activated cyclic nucleotide-gated (HCN) channel bolsters the activity of bitter-sensing gustatory receptor neurons (bGRNs), albeit acting in sweet-sensing GRNs (sGRNs). For this task, HCN maintains SP despite prolonged sGRN stimulation induced by the diet mimicking their sweet feeding niche, such as overripe fruit. We present evidence that Ih-dependent demarcation of sGRN excitability is implemented to throttle SP consumption, which may have facilitated adaptation to a sweetness-dominated environment. Thus, HCN expressed in sGRNs serves as a key component of a simple yet versatile peripheral coding that regulates bitterness for optimal food intake in two contrasting ways: sweet-resilient preservation of bitter aversion and the previously reported sweet-dependent suppression of bitter taste.

Identification and characterization of olfactory gene families in Macrobrachium rosenbergii based on full-length transcripts and genome sequences

The olfactory gene families include odorant binding proteins (OBPs), chemosensory proteins (CSPs), olfactory receptors (ORs), ionotropic receptors (IRs) and gustatory receptors (GRs). To investigate the molecular function of olfactory perception in Macrobrachium rosenbergii, we integrated the full-length transcripts and whole-genome sequences to identify the olfactory gene families. In this study, a total of 38,955 full-length transcripts with an N50 length of 3383 bp were obtained through PacBio SMRT sequencing. Through the annotation of full-length transcripts and whole-genome sequences, several olfactory gene families were identified, including 18 MrORs, 16 MrIRs, 151 MrIGluRs (ionotropic glutamate receptors), 2 MrVIGluRs (variant ionotropic glutamate receptors) and 3 MrCRs (chemosensory receptors). Notably, the CRs were first identified in prawns and shrimps. Additionally, the olfactory gene families in M. nipponense were identified, comprising 4 MnORs, 21 MnIRs, 79 MnIGluRs, 5 MnVIGluRs, 1 MnGR and 1 MnOBP, using the available whole-genome sequences. Meanwhile, the external morphology of the chemical sensory organs of M. rosenbergii was explored, and the presence of plumose setae (PS), hard thorn setae (HTS), bamboo shoot setae (BSS), soft thorn setae (STS) and aesthetascs (AE) on the antennules, HTS and BSS on the second antennae, and PS on the pereiopods were observed by scanning electron microscope. This study provides valuable insights for future functional studies into the olfactory perception of crustaceans and establishes a theoretical basis for molecular design breeding in M. rosenbergii.

Stop Codon Usage of Three Gene Families in Selected Medical Insects, and their Phylogenetic Relationships

Medical insects pose significant health risks, transmitting disease causing agents with significant morbidity and mortality globally. Understanding their genetic composition and evolutionary relationship is crucial to developing control techniques to combat them. This study aims to compare the stop codon usage of gustatory, odorant and kinase genes, and assess their use as markers for evaluating the phylogenetic relationship between selected medical insects. Fifteen genes from three gene families including gustatory receptors, odorant receptors, and kinases were studied in thirty-four insect species. Gene and transcript sequences were retrieved from Ensembl Metazoa database. The stop codon usage was obtained by identifying the stop codon present at the end of the transcript sequences. Multiple sequence alignment of the gene sequences was performed and phylogenetic trees were computed. There were variations in the stop codon usage across the different insect species. The odorant receptor and kinase genes grouped the insects into two major clusters. The stop codon usage highlighted the variation within and among the species. The phylogenetic analysis results supported existing insect classification. These approaches could be considered for phylogenetic analyses of other arthropod groups. Accurate measurement of stop codon usage will be important for understanding natural selection, the genetic variation of coding sequences of genes, and useful in design of more efficient expression constructs in gene-editing techniques for vector control.

Antennal transcriptome analysis reveals sensory receptors potentially associated with host detection in the livestock pest Lucilia cuprina

BackgroundLucilia cuprina (Wiedemann, 1830) (Diptera: Calliphoridae) is the main causative agent of flystrike of sheep in Australia and New Zealand. Female flies lay eggs in an open wound or natural orifice, and the developing larvae eat the host’s tissues, a condition called myiasis. To improve our understanding of host-seeking behavior, we quantified gene expression in male and female antennae based on their behavior.MethodsA spatial olfactometer was used to evaluate the olfactory response of L. cuprina mated males and gravid females to fresh or rotting beef. Antennal RNA-Seq analysis was used to identify sensory receptors differentially expressed between groups.ResultsLucilia cuprina females were more attracted to rotten compared to fresh beef (> fivefold increase). However, males and some females did not respond to either type of beef. RNA-Seq analysis was performed on antennae dissected from attracted females, non-attracted females and males. Transcripts encoding sensory receptors from 11 gene families were identified above a threshold (≥ 5 transcript per million) including 49 ATP-binding cassette transporters (ABCs), two ammonium transporters (AMTs), 37 odorant receptors (ORs), 16 ionotropic receptors (IRs), 5 gustatory receptors (GRs), 22 odorant-binding proteins (OBPs), 9 CD36-sensory neuron membrane proteins (CD36/SNMPs), 4 chemosensory proteins (CSPs), 4 myeloid lipid-recognition (ML) and Niemann-Pick C2 disease proteins (ML/NPC2), 2 pickpocket receptors (PPKs) and 3 transient receptor potential channels (TRPs). Differential expression analyses identified sex-biased sensory receptors.ConclusionsWe identified sensory receptors that were differentially expressed between the antennae of both sexes and hence may be associated with host detection by female flies. The most promising for future investigations were as follows: an odorant receptor (LcupOR46) which is female-biased in L. cuprina and Cochliomyia hominivorax Coquerel, 1858; an ABC transporter (ABC G23.1) that was the sole sensory receptor upregulated in the antennae of females attracted to rotting beef compared to non-attracted females; a female-biased ammonia transporter (AMT_Rh50), which was previously associated with ammonium detection in Drosophila melanogaster Meigen, 1830. This is the first report suggesting a possible role for ABC transporters in L. cuprina olfaction and potentially in other insects.Graphical

HcGr76 responds to fructose and chlorogenic acid and is involved in regulation of peptide expression in the midgut of Hyphantria cunea larvae.

Sensing dietary components in the gut is important to ensure an appropriate hormonal response and metabolic regulation after food intake. The fall webworm, Hyphantria cunea, is a major invasive pest in China and has led to significant economic losses and ecosystem disruption. The larvae's broad host range and voracious appetite for leaves make H. cunea a primary cause of serious damage to both forests and crops. To date, however, the gustatory receptors (Grs) of H. cunea and their regulatory function remain largely unknown. We identified the fall webworm gustatory receptor HcGr76 as a fructose and chlorogenic acid receptor using Ca2+ imaging and determination of intracellular Ca2+ concentration by a microplate reader. Moreover, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis revealed that HcGr76 is highly expressed in the anterior and middle midgut. Knockdown of HcGr76 caused a significant reduction in the expression of neuropeptide F 1 (NPF1) and CCHamide-2, and led to a decrease in carbohydrate and lipid levels in the hemolymph. Our studies provide circumstantial evidence that HcGr76 expressed in the midgut is involved in sensing dietary components, and regulates the expression of relevant peptide hormones to alter metabolism in H. cunea larvae, thus providing a promising molecular target for the development of new insect-specific control products. © 2024 Society of Chemical Industry.

Transcriptome and differential expression analysis of chemosensory genes in the antennae and heads of Apis cerana cerana drones

The olfactory system plays a critical role in honey bee adaptation to complex and constantly changing environments, as well as in the maintenance of social cohesion. Honey bees have evolved a sophisticated chemical communication system to regulate their intricate social interactions. Despite there is a preliminary understanding of the components, cells, and physiological pathways involved in pheromone response, the molecular mechanisms underlying honey bee drones’ mating behavior and pheromone communication remain largely unknown. This study presented the first comprehensive transcriptome analysis of the antennae and heads of Apis cerana cerana drones in response to 9-ODA. Based on gene ontology and KEGG pathway, we found the majority of differentially expressed genes associated with molecular functions and signal transduction. Additionally, we identified 153 genes closely related to olfaction in the transcriptome datasets, including 111 odorant receptors (ORs), 16 odorant-binding proteins (OBPs), nine ionotropic receptors (IRs), 10 gustatory receptors (GRs), five chemosensory proteins (CSPs), and two sensory neuron membrane proteins (SNMPs), and most of them showed relatively high expression levels in the drone antennae. The reliability of these differential genes was validated using RT-qPCR. Our results will contribute to detect the molecular mechanisms of odorant and investigate olfactory functions in the Asian honey bees.