Ligand carrier protein genes expressed in larval chemosensory organs of Bombyx mori

CRISPR/Cas9-mediated knockout of a male accessory glands-specific gene takeout1 decreases the fecundity of Zeugodacus cucurbitae female

BACKGROUND

The melon fly, Zeugodacus cucurbitae (Coquillett), is an invasive Tephritidae pest with robust fertility. The male accessory glands (MAGs) form a vital organ that ensures insect reproductive efficiency. Most of the secreted proteins by MAGs exhibit a male bias expression. Takeout, one of these proteins, is abundantly present in the MAGs of many insects.

RESULTS

In this study, we identified 32 takeout genes in Z. cucurbitae. The phylogenetic analysis and multiple sequence alignment results showed that Zctakeout1 is the most related homolog to the MAGs-specific takeout in Tephritidae. The real-time quantitative PCR results showed that Zctakeout1 was exclusively expressed in the male adult stage, and its expression level gradually increased with the increase in age and then remained stable at the sexually matured stage. The distribution among tissues demonstrated the specific expression of Zctakeout1 in the MAGs, and fluorescence immunohistochemical results confirmed the presence of Zctakeout1 in close proximity to binuclear cells of the mesoderm epidermal MAGs. In continuation, CRISPR/Cas9-mediated genome editing was employed, resulting in successfully generating a homozygous strain with an +8 bp insertion. The mating experiments with the Zctakeout1-/- males resulted in significant reductions in both the mating rate and egg production of females.

CONCLUSION

These findings prove that the MAGs-specific Zctakeout1 is essential in regulating fecundity in female Z. cucurbitae fruit flies. Our data suggests its utilization in future essential insect-specific gene-directed sterility insect technique (SIT) by the genetic manipulation to keep these important Tephritidae populations under control. © 2024 Society of Chemical Industry.

Identification and analysis of JHBP/TO family genes and their roles in the reproductive fitness cost of resistance in Frankliniella occidentalis (Pergande)

The juvenile hormone binding protein (JHBP) and takeout (TO) genes, mediated by the juvenile hormone (JH), play a crucial role in regulating the reproductive physiology of insects. Our previous study revealed that spinosad-resistant Frankliniella occidentalis (NIL-R) exhibited reduced fecundity and significant changes in JHBP/TO family gene expression. We hypothesized that these genes were involved in regulating the fitness costs associated with resistance. In this study, 45 JHBP/TO genes were identified in F. occidentalis, among which FoTO2 and FoTO10 were duplicates. Additionally, eight genes exhibited significant down-regulation in the NIL-R population. Two genes (FoTO6 and FoTO24) that exhibited the most significant differential expression between the spinosad-susceptible (Ivf03) and NIL-R populations were selected to investigate their roles in resistance fitness using RNA interference (RNAi). Following interference with FoTO6, FoTO24, and their combination, the expression levels of vitellogenin (Vg) were downregulated by 3%-30%, 13%-28%, and 14%-32% from the 2nd day to the 5th day, respectively; Krüppel-homolog 1 (Kr-h1) expression was down-regulated by 3%-65%, 11%-34%, and 11%-39% from the 2nd day to the 5th day, respectively; ovariole length was shortened by approximately 18%, 21%, and 24%, respectively; and the average number of eggs decreased from 407 to 260, 148, and 106, respectively. Additionally, a JH supplementation experiment on the NIL-R population revealed that the expression levels of both FoTO6, FoTO24, Vg and Kr-h1 were significantly upregulated compared with those observed in the Ivf03 population, resulting in increased fecundity. These results suggest that FoTO6 and FoTO24 are involved in JH-mediated regulation of the reproductive fitness cost of resistance to spinosad. Further, FoTO6 and FoTO24 can be considered potential target genes for applying RNAi technology in the scientific management of F. occidentalis.

Social environment affects sensory gene expression in ant larvae

Social insects depend on communication to regulate social behaviour. This also applies to their larvae, which are commonly exposed to social interactions and can react to social stimulation. However, how social insect larvae sense their environment is not known. Using RNAseq, we characterized expression of sensory-related genes in larvae of the ant Formica fusca, upon exposure to two social environments: isolation without contact to other individuals, and stimulation via the presence of other developing individuals. Expression of key sensory-related genes was higher following social stimulation, and larvae expressed many of the same sensory-related genes as adult ants and larvae of other insects, including genes belonging to the major insect chemosensory gene families. Our study provides first insights into the molecular changes associated with social information perception in social insect larvae.

The Expression of UGT46A1 Gene and Its Effect on Silkworm Feeding

The silkworm, Bombyx mori, uses a complex olfactory system to determine whether the food is edible. As an odor degrading enzyme, UDP-glycosyltransferase (UGT) participates in the degradation of odor molecules in the olfactory system of the silkworm. By sequencing the whole genome of the silkworm NB and using comparative genomics methods, we found that UGT46A1 is unique in species that eat mulberry leaves. Bioinformatics shows that its function may be related to the feeding habits of the silkworm. In this study, it was found through quantitative real-time polymerase chain reaction (qRT-PCR) that UGT46A1 was highly expressed in the heads of silkworms, which was consistent with the conjecture that UGT46A1 was involved in silkworm olfactory recognition. RNA interference (RNAi) was used to knock down the expression of UGT46A1. By observing the silkworm’s tendency toward mulberry leaves and food selectivity, it was found that the silkworms that successfully knocked down the UGT46A1 gene altered their feeding habits and that their ability to find food was weakened, but they could eat more leaves of plants other than mulberry leaves. This evidence indicates that UGT46A1 may affect the silkworm’s feeding by influencing the olfactory system of the silkworm.

Characterization of Rhopalosiphum padi takeout-like genes and their role in insecticide susceptibility

Due to the extensive use of chemical insecticides, the field populations of Rhopalosiphum padi, a serious wheat pest worldwide, have developed resistance to insecticides. Therefore, deep understanding of the mechanisms of the aphid's physiological response to insecticides would be of importance for the management of insecticide resistance in pests. Takeout belongs to a protein superfamily found exclusively in insects. Previous research showed that the takeout gene had various functions in insect physiology and behavior. However, few studies have explored the functions of takeout in insect insecticide susceptibility. The susceptibility of R. padi to imidacloprid and beta-cypermethrin was tested. Thirteen takeout-like genes were identified based on the genome database of R. padi. The number of exons was variable in these takeout-like genes, and nine highly conserved amino acids (two Cysteine, two Proline, four Glycine and one Aspartic acid) were identified. Expression levels of takeout-like-2, takeout-like-3, takeout-like-5, takeout-like-8, takeout-like-10 and takeout-like-11 were significantly increased after imidacloprid treatment; seven genes (takeout-like-1, takeout-like-2, takeout-like-5, takeout-like-6, takeout-like-7, takeout-like-8 and takeout-like-11) tended to be upregulated after beta-cypermethrin treatment. RNA interference results showed that the mortalities of R. padi injected with dsTOL-2, dsTOL-5, dsTOL-8, dsTOL-10 and dsTOL-11 were significantly increased after exposure to imidacloprid in comparison with control (injection of dsGFP). Under two sublethal concentrations of beta-cypermethrin, the silencing of takeout-like-2, takeout-like-5 and takeout-like-11 significantly increased the mortalities of R. padi. These results provide evidence for the involvement of takeout-like genes in insecticide susceptibility of R. padi, which improves our understanding the determinant of insecticide susceptibility.

A Chemosensory Protein Detects Antifeedant in Locust (Locusta migratoria)

Simple Summary

Chemosensory proteins (CSPs) in insects are small compact polypeptides which can bind and carry hydrophobic semiochemicals. CSPs distribute in many organs of insect and have multiple functions. In chemosensory system, CSPs are thought to be responsible for detecting chemical signals from the environment. In this study, we proved that LmigCSPIII, a CSP in Locusta migratoria is involved in detecting an antifeedant. LmigCSPIII exhibits high binding affinity to α-amylcinnamaldehyde, a natural compound from non-host plant which was subsequently demonstrated to be an effective antifeedant. Knockdown of LmigCSPIII gene by RNA interference showed reduced sensitivity to α-amylcinnamaldehyde but showed no changes in their physiological development or food consumption. Our findings provided new evidence that CSPs can detect antifeedant in chemosensory system of insects.

Abstract

Chemosensory system is vitally important for animals to select food. Antifeedants that herbivores encounter can interfere with feeding behavior and exert physiological effects. Few studies have assessed the molecular mechanisms underlying the chemoreception of antifeedants. In this study, we demonstrated that a chemosensory protein (CSP) in Locusta migratoria is involved in detecting an antifeedant. This CSP, LmigEST6 (GenBank Acc. No. AJ973420), we named as LmigCSPIII, expressed in sensory organs where chemosensilla are widely distributed. Fluorescent binding experiments indicated that LmigCSPIII exhibits high binding affinity to α-amylcinnamaldehyde (AMCAL), a natural compound from non-host plant. This compound was subsequently demonstrated to be an effective antifeedant to locusts in feeding bioassay. By injection of double-stranded RNA (dsRNA) of LmigCSPIII, we generated LmigCSPIII knockdown locusts. The feeding behaviour assays demonstrated that the LmigCSPIII knockdown locusts had reduced sensitivity to the antifeedant but showed no changes in their physiological development or food consumption. Therefore, we inferred that this chemosensory protein is involved in antifeedant detection.

Expression Profiles and Biochemical Analysis of Chemosensory Protein 3 from Nilaparvata lugens (Hemiptera: Delphacidae)

Insects have evolved highly sensitive olfactory sensory systems to detect plant hosts and mates, with plant volatiles playing an important role in informing insect behavior. Chemosensory proteins (CSPs) are thought to play a key role in this process, but in this respect, there is limited information on brown planthopper Nilaparvata lugens, one of the most destructive pests of rice. To expand our understanding of CSP function in N. lugens we explored expression profiles and binding characteristics of NlugCSP3. The ligands with higher binding affinity were also validated by molecular docking and behavioral assays. NlugCSP3 mRNA was expressed at relatively higher levels in antennae and abdomen of 3-day-old unmated macropterous males as well as in antennae of 3-day mated macropterous and brachypterous females. Fluorescence competitive binding assays revealed that 5 out of 25 candidate volatiles are strong binders (Ki < 10 μM). Behavioral assays revealed that nonadecane and 2-tridecanone, which have high binding affinities in fluorescence competition-binding assays, displayed strong attractiveness to N. lugens. Pursuing this further, molecular docking analysis identified key amino acid residues involved in binding volatile compounds. Overall, our data provide a base for further investigation of the potential physiological functions of CSP3 in Nilaparvata lugens, and extend the function of NlugCSP3 in chemoreception of N. lugens.

Collisional mechanism of ligand release by Bombyxmori JHBP, a member of the TULIP / Takeout family of lipid transporters

Juvenile hormones (JHs) regulate important processes in insects, such as postembryonic development and reproduction. In the hemolymph of Lepidoptera, these lipophilic sesquiterpenic hormones are transported from their site of synthesis to target tissues by high affinity carriers, the juvenile hormone binding proteins (JHBPs). Lepidopteran JHBPs belong to a recently uncovered, yet very ancient family of proteins sharing a common lipid fold (TULIP domain) and involved in shuttling various lipid ligands. One important, but poorly understood aspect of JHs action, is the mechanism of hormone transfer to or through the plasma membranes of target cells. Since many membrane-active peptides and proteins, such as the pore-forming bacterial toxins, are activated by low pH or interaction with phospholipid membranes, we have examined the effect of these factors on JH binding by JHBPs. The affinity of Bombyx mori and Manduca sexta JHBPs for JH III was determined by the DCC assay, equilibrium dialysis, and isothermal titration calorimetry, and found to be greatly reduced at low pH, in agreement with previous observations. Loss of binding was accompanied by changes in fluorescence and near-UV CD spectra, indicating significant changes in protein structure in the environment of aromatic residues. The apparent dissociation rate constant (k_off) of the JHBP-JH III complex was greater at acidic pH, suggesting that low pH favors ligand release by opening of the binding pocket. The affinity of recombinant B. mori JHBP (rBmJHBP) was also decreased in the presence of anionic phospholipid vesicles. Measurements of steady-state fluorescence anisotropy with the lipophilic probe TMA-DPH demonstrated that rBmJHBP specifically interacts with anionic membranes. These results suggest the existence of a collisional mechanism for ligand release that may be important for delivery of JHs to the target cells, and could be relevant to the function of related members of this emerging family of lipid-transport proteins.

Identification of Odorant-Binding Proteins (OBPs) and Functional Analysis of Phase-Related OBPs in the Migratory Locust

Olfactory plasticity, which is one of the major characteristics of density-dependent phase polyphenism, plays critical roles in the large-scale aggregation formation of Locusta migratoria. It is still unknown whether odorant-binding proteins (OBPs) are involved in phase-related olfactory plasticity of locusts, despite the confirmed involvement of several types of olfactory perception genes. In this study, we performed a large-scale search for OBPs and verified their expression patterns in the migratory locust. We identified 17 OBPs in the L. migratoria genome, of which 10 were novel, and we found their scattering distribution characteristics by mapping the genomic loci. Next, we revealed that these OBPs with close phylogenic relationships displayed similar tissue-specific expression profiles by a combined analysis of qRT-PCR and phylogenetic tree reconstruction. In all identified locust OBPs, seven OBPs showed differential mRNA expression levels in antenna tissue between gregarious and solitarious nymphs. Six of these seven OBPs displayed higher mRNA expression in the antennae of gregarious nymphs. The mRNA expression of LmigOBP2 and LmigOBP4 increased during gregarization and decreased during solitarization. RNAi experiments confirmed that only LmigOBP4 regulates the behavioral traits to affect gregarious behavior. These results demonstrated that OBPs also play important roles in the regulation of phase-related behavior of the locusts.

Silencing of Chemosensory Protein Gene NlugCSP8 by RNAi Induces Declining Behavioral Responses of Nilaparvata lugens

Chemosensory proteins (CSPs) play imperative functions in chemical and biochemical signaling of insects, as they distinguish and transfer ecological chemical indications to a sensory system in order to initiate behavioral responses. The brown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera: Delphacidae), has emerged as the most destructive pest, causing serious damage to rice in extensive areas throughout Asia. Biotic characteristics like monophagy, dual wing forms, and annual long-distance migration imply a critical role of chemoreception in N. lugens. In this study, we cloned the full-length CSP8 gene from N. lugens. Protein sequence analysis indicated that NlugCSP8 shared high sequence resemblance with the CSPs of other insect family members and had the typical four-cysteine signature. Analysis of gene expression indicated that NlugCSP8 mRNA was specifically expressed in the wings of mated 3-day brachypterous females with a 175-fold difference compare to unmated 3-day brachypterous females. The NlugCSP8 mRNA was also highly expressed in the abdomen of unmated 5-day brachypterous males and correlated to the age, gender, adult wing form, and mating status. A competitive ligand-binding assay demonstrated that ligands with long chain carbon atoms, nerolidol, hexanal, and trans-2-hexenal were able to bind to NlugCSP8 in declining order of affinity. By using bioinformatics techniques, three-dimensional protein structure modeling and molecular docking, the binding sites of NlugCSP8 to the volatiles which had high binding affinity were predicted. In addition, behavioral experiments using the compounds displaying the high binding affinity for the NlugCSP8, revealed four compounds able to elicit significant behavioral responses from N. lugens. The in vivo functions of NlugCSP8 were further confirmed through the testing of RNAi and post-RNAi behavioral experiments. The results revealed that reduction in NlugCSP8 transcript abundance caused a decrease in behavioral response to representative attractants. An enhanced understanding of the NlugCSP8 is expected to contribute in the improvement of more effective and eco-friendly control strategies of BPH.

Identification, Expression Patterns, and Functional Characterization of Chemosensory Proteins in Dendroctonus armandi (Coleoptera: Curculionidae: Scolytinae)

The Chinese white pine beetle, Dendroctonus armandi Tsai and Li (Coleoptera: Curculionidae: Scolytinae), is a serious pest of coniferous forests in China. Thus, there is considerable interest in developing eco-friendly pest-control methods, with the use of semiochemicals as a distinct possibility. Olfaction is extremely important for fitness of D. armandi because it is the primary mechanism through which the insect locates hosts and mates. Thus, here we characterized nine full-length genes encoding chemosensory proteins (CSPs) from D. armandi. The genes were ubiquitously and multiply expressed across different developmental stages and adult tissues, indicating various roles in developmental metamorphosis, olfaction, and gustation. Ligand-binding assays implied that DarmCSP2 may be the carrier of D. armandi pheromones and various plant host volatiles. These volatiles were identified through RNA interference of DarmCSP2 as: (+)-α-pinene, (+)-β-pinene, (−)-β-pinene, (+)-camphene, (+)-3-carene, and myrcene. The systematic chemosensory functional analysis of DarmCSP2 in this study clarified the molecular mechanisms underlying D. armandi olfaction and provided a theoretical foundation for eco-friendly pest control.

Expression of a sugar clade gustatory receptor, BmGr6, in the oral sensory organs, midgut, and central nervous system of larvae of the silkworm Bombyx mori

Insects taste nonvolatile chemicals through gustatory receptors (Grs) and make choices for feeding, mating, and oviposition. To date, genome projects have identified 69 Gr genes in the silkworm, Bombyx mori; however, the expression sites of these Grs remain to be explored. In this study, we used reverse transcription (RT)-PCR to investigate expression of the B. mori Gr-6 (BmGr6) gene, a member of the putative sugar clade gene family in various tissues. BmGr6 is expressed in the midgut, central nervous system (CNS), and oral sensory organs. Moreover, immunohistochemistry using an anti-BmGr6 antiserum demonstrated that BmGr6 is expressed in cells by oral sensory organs, midgut and nervous system. Furthermore, double-immunohistochemistry indicated that BmGr6 is expressed in midgut enteroendocrine cells, also in CNS neurosecretory cells. In particular, a portion of BmGr6-expressing cells, in both midgut and CNS, secretes FMRFamide-related peptides (FaRPs). These results suggest that BmGr6 functions not only as a taste receptor, but also as a chemical sensor such as for the regulation of gut movement, physiological conditions, and feeding behavior of larvae.

Identification, expression profiling and fluorescence-based binding assays of a chemosensory protein gene from the Western flower thrips, Frankliniella occidentalis

Using RT-PCR and RACE-PCR strategies, we cloned and identified a new chemosensory protein (FoccCSP) from the Western flower thrips, Frankliniella occidentalis, a species for which no chemosensory protein (CSP) has yet been identified. The FoccCSP gene contains a 387 bp open-reading frame encoding a putative protein of 128 amino acids with a molecular weight of 14.51 kDa and an isoelectric point of 5.41. The deduced amino acid sequence contains a putative signal peptide of 19 amino acid residues at the N-terminus, as well as the typical four-cysteine signature found in other insect CSPs. As FoccCSP is from a different order of insect than other known CSPs, the GenBank FoccCSP homolog showed only 31-50% sequence identity with them. A neighbor-joining tree was constructed and revealed that FoccCSP is in a group with CSPs from Homopteran insects (e.g., AgosCSP4, AgosCSP10, ApisCSP, and NlugCSP9), suggesting that these genes likely developed from a common ancestral gene. The FoccCSP gene expression profile of different tissues and development stages was measured by quantitative real-time PCR. The results of this analysis revealed this gene is predominantly expressed in the antennae and also highly expressed in the first instar nymph, suggesting a function for FoccCSP in olfactory reception and in particular life activities during the first instar nymph stage. We expressed recombinant FoccCSP protein in a prokaryotic expression system and purified FoccCSP protein by affinity chromatography using a Ni-NTA-Sepharose column. Using N-phenyl-1-naphthylamine (1-NPN) as a fluorescent probe in fluorescence-based competitive binding assay, we determined the binding affinities of 19 volatile substances for FoccCSP protein. This analysis revealed that anisic aldehyde, geraniol and methyl salicylate have high binding affinities for FoccCSP, with KD values of 10.50, 15.35 and 35.24 μM, respectively. Thus, our study indicates that FoccCSP may play an important role in regulating the development of the first instar nymph and mediate F. occidentalis host recognition.

Starvation-responsive glycine-rich protein gene in the silkworm Bombyx mori

Four glycine-rich protein (GRP) genes were identified from expressed sequence tags of the maxillary galea of the silkworm. All four genes were expressed in the maxillary pulp, antenna, labrum, and labium, but none of the genes were expressed in most internal organs. Expression of one of the genes, termed bmSIGRP, was further increased approximately fivefold in the mouth region (including the maxilla, antenna, labrum, labium, and mandible) after 24 h of starvation. bmSIGRP expression peaked at 24 h and gradually declined during the subsequent 2 days. When a synthetic diet not containing proteins was fed, bmSIGRP expression increased significantly in the mouth region to levels similar to that observed in starved larvae. Synthetic diets that lacked vitamins or salts but contained amino acids did not significantly affect bmSIGRP expression. These results suggest that amino acid depletion increases bmSIGRP expression.

Daily rhythms in antennal protein and olfactory sensitivity in the malaria mosquito Anopheles gambiae

We recently characterized 24-hr daily rhythmic patterns of gene expression in Anopheles gambiae mosquitoes. These include numerous odorant binding proteins (OBPs), soluble odorant carrying proteins enriched in olfactory organs. Here we demonstrate that multiple rhythmically expressed genes including OBPs and takeout proteins, involved in regulating blood feeding behavior, have corresponding rhythmic protein levels as measured by quantitative proteomics. This includes AgamOBP1, previously shown as important to An. gambiae odorant sensing. Further, electrophysiological investigations demonstrate time-of-day specific differences in olfactory sensitivity of antennae to major host-derived odorants. The pre-dusk/dusk peaks in OBPs and takeout gene expression correspond with peak protein abundance at night, and in turn coincide with the time of increased olfactory sensitivity to odorants requiring OBPs and times of increased blood-feeding behavior. This suggests an important role for OBPs in modulating temporal changes in odorant sensitivity, enabling the olfactory system to coordinate with the circadian niche of An. gambiae.

Comparative genomics of odorant binding proteins in Anopheles gambiae, Aedes aegypti, and Culex quinquefasciatus

About 1 million people in the world die each year from diseases spread by mosquitoes, and understanding the mechanism of host identification by the mosquitoes through olfaction is at stake. The role of odorant binding proteins (OBPs) in the primary molecular events of olfaction in mosquitoes is becoming an important focus of biological research in this area. Here, we present a comprehensive comparative genomics study of OBPs in the three disease-transmitting mosquito species Anopheles gambiae, Aedes aegypti, and Culex quinquefasciatus starting with the identification of 110 new OBPs in these three genomes. We have characterized their genomic distribution and orthologous and phylogenetic relationships. The diversity and expansion observed with respect to the Aedes and Culex genomes suggests that the OBP gene family acquired functional diversity concurrently with functional constraints posed on these two species. Sequences with unique features have been characterized such as the "two-domain OBPs" (previously known as Atypical OBPs) and "MinusC OBPs" in mosquito genomes. The extensive comparative genomics featured in this work hence provides useful primary insights into the role of OBPs in the molecular adaptations of mosquito olfactory system and could provide more clues for the identification of potential targets for insect repellants and attractants.

Crystal structure of Apis mellifera OBP14, a C-minus odorant-binding protein, and its complexes with odorant molecules

Apis mellifera (Amel) relies on its olfactory system to detect and identify new-sources of floral food. The Odorant-Binding Proteins (OBPs) are the first proteins involved in odorant recognition and interaction, before activation of the olfactory receptors. The Amel genome possess a set of 21 OBPs, much fewer compared to the 60-70 OBPs found in Diptera genomes. We have undertaken a structural proteomics study of Amel OBPs, alone or in complex with odorant or model compounds. We report here the first 3D structure of a member of the C-minus class OBPs, AmelOBP14, characterized by only two disulfide bridges of the three typical of classical OBPs. We show that AmelOBP14 possesses a core of 6 α-helices comparable to that of classical OBPs, and an extra exposed C-terminal helix. Its binding site is located within this core and is completely closed. Fluorescent experiments using 1-NPN displacement demonstrate that AmelOBP14 is able to bind several compounds with sub micromolar dissociation constants, among which citralva and eugenol exhibit the highest affinities. We have determined the structures of AmelOBP14 in complex with 1-NPN, eugenol and citralva, explaining their strong binding. Finally, by introducing a double cysteine mutant at positions 44 and 97, we show that a third disulfide bridge was formed in the same position as in classical OBPs without disturbing the fold of AmelOBP14.