Repellency Mechanism of Natural Guar Gum-Based Film Incorporated with Citral against Brown Planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

Using of plant essential oil that coevolved as a defense mechanism against agriculture insects is an alternative means of controlling many insect pests. In order to repel brown planthoppers (BPHs), the most notorious rice insect pest, a new film based on guar gum incorporated with citral (GC film) was formulated, which was effective while being environmentally friendly. In this paper, the effect and mechanism of GC film repellency against BPHs were determined. Repellent activity test and olfactory reaction analysis showed that GC film had repellency effect against BPHs, with repellency of 60.00% and 73.93%, respectively. The result of olfactory reaction indicated that GC film repellency against BPHs relied on smell. EPG analysis showed the proportion and mean duration of np waveform were significantly higher than in CK and increased following the treatment concentration, which indicated that GC film affected the recognition of BPHs to rice. Further analysis by RNA sequencing analysis showed a total of 679 genes were significantly upregulated and 284 genes were significantly downregulated in the BPHs fed on the rice sprayed with GC film compared to control. Odorant-binding protein (OBP) gene 797 and gustatory receptor gene (GR)/odorant receptor (OR) gene 13110 showed a significant decrease in differential expression and significant increase in differential expression, respectively. There were 0.66 and 2.55 differential expression multiples between treated BPHs and control, respectively. According to the results described above, we reasoned that GC film repellency against BPHs due to smell, by release of citral, caused the recognition difficulties for BPHs to rice, and OBP gene 797 and GR/OR gene 13110 appeared to be the crucial candidate genes for GC film repellency against BPHs. The present study depicted a clear and consistent repellency effect for GC film against BPHs and preliminarily clarified the mechanism of GC film as a repellent against BPHs, which might offer an alternative approach for control of BPHs in the near future. Our results could also help in the development and improvement of GC films.

Screening for Odorant Receptor Genes Expressed in Aedes Aegypti Involved in Blood-Feeding and Oviposition Behaviors

Background: Aedes aegypti is one of the most important vector worldwide, and its survival and reproductive processes depend heavily on the olfactory system. In this study, the expression levels of all odorant receptor (OR) genes of Ae. aegypti were explored in different physiological periods to identify olfactory genes that may be associated with mosquito blood sucking and searching for oviposition sites.Methods: Four groups, consisting of Ae. aegypti males (M), pre-blood-feeding females (F), post-blood-feeding females (B) and post-oviposition females (O), were established. A total of 114 pairs of primer targeting all OR genes were designed based on the whole genome of Ae. aegypti. The expression of OR genes was evaluated by real-time fluorescence quantitative PCR for relative quantification and the comparison of differences between groups.Results: A total of 53 differentially expressed OR genes were identified between males and females in Ae. aegypti antennae. And 8, 5 and 13 differentially expressed OR genes were identified before versus after blood feeding, before versus after oviposition and post-blood-feeding versus post-oviposition, respectively. Meanwhile, 16 OR genes were significantly differentially expressed in multiple physiological periods of mosquitoes.Conclusions: A large number of ORs with significant intergroup differences and high expression levels were screened in this study, including OR75, OR88, OR110 and OR115 and so on. Some of these genes are reported for the first time, providing possible targets for the development of mosquito control pathways based on the olfactory system.

Human APOE ɛ3 and APOE ɛ4 Alleles Have Differential Effects on Mouse Olfactory Epithelium

Background: Alzheimer’s disease (AD) is a progressive age-dependent disorder whose risk is affected by genetic factors. Better models for investigating early effects of risk factors such as apolipoprotein E (APOE) genotype are needed. Objective: To determine whether APOE genotype produces neuropathologies in an AD-susceptible neural system, we compared effects of human APOE ɛ3 (E3) and APOE ɛ4 (E4) alleles on the mouse olfactory epithelium. Methods: RNA-Seq using the STAR aligner and DESeq2, immunohistochemistry for activated caspase-3 and phosphorylated histone H3, glucose uptake after oral gavage of 2-[1,2-3H (N)]-deoxy-D-glucose, and Seahorse Mito Stress tests on dissociated olfactory mucosal cells. Results: E3 and E4 olfactory mucosae show 121 differentially abundant mRNAs at age 6 months. These do not indicate differences in cell type proportions, but effects on 17 odorant receptor mRNAs suggest small differences in tissue development. Ten oxidoreductases mRNAs important for cellular metabolism and mitochondria are less abundant in E4 olfactory mucosae but this does not translate into differences in cellular respiration. E4 olfactory mucosae show lower glucose uptake, characteristic of AD susceptibility and consistent with greater expression of the glucose-sensitive gene, Asns. Olfactory sensory neuron apoptosis is unaffected at age 6 months but is greater in E4 mice at 10 months. Conclusion: Effects of human APOE alleles on mouse olfactory epithelium phenotype are apparent in early adulthood, and neuronal loss begins to increase by middle age (10 months). The olfactory epithelium is an appropriate model for the ability of human APOE alleles to modulate age-dependent effects associated with the progression of AD.

Identification of functional residues using machine learning provides insights into the evolution of odorant receptor gene families in solitary and social insects

The gene family of insect odorant receptors (ORs) has greatly expanded in the course of evolution. ORs allow insects to detect volatile chemicals and therefore play an important role in social interactions, the detection of enemies and preys, and during foraging. The sequences of several thousand ORs are known, but their specific function or ligands have been identified only for very few of them. To advance the functional characterization of ORs, we compiled, curated and aligned the sequences of 3,902 ORs from 21 insect species. We identified the amino acid positions that best predict the response to ligands using machine learning on sets of functionally characterized proteins from the fly Drosophila melanogaster, the mosquito Anopheles gambiae and the ant Harpegnathos saltator. We studied the conservation of these predicted relevant residues across all OR subfamilies and show that the subfamilies that expanded strongly in social insects exhibit high levels of conservation in their binding sites. This indicates that ORs of social insect families are typically finely tuned and exhibit a sensitivity to very similar odorants. Our novel approach provides a powerful tool to use functional information from a limited number of genes to investigate the functional evolution of large gene families.

Stage-specific expression of an odorant receptor underlies olfactory behavioral plasticity in Spodoptera littoralis larvae

Background The detection of environmental cues and signals via the sensory system directs behavioral choices in diverse organisms. Insect larvae rely on input from the chemosensory system, mainly olfaction, for locating food sources. In several lepidopteran species, foraging behavior and food preferences change across larval instars; however, the molecular mechanisms underlying such behavioral plasticity during larval development are not fully understood. Here, we hypothesize that expression patterns of odorant receptors (ORs) change during development, as a possible mechanism influencing instar-specific olfactory-guided behavior and food preferences. Results We investigated the expression patterns of ORs in larvae of the cotton leafworm Spodoptera littoralis between the first and fourth instar and revealed that some of the ORs show instar-specific expression. We functionally characterized one OR expressed in the first instar, SlitOR40, as responding to the plant volatile, β-caryophyllene and its isomer α-humulene. In agreement with the proposed hypothesis, we showed that first but not fourth instar larvae responded behaviorally to β-caryophyllene and α-humulene. Moreover, knocking out this odorant receptor via CRISPR-Cas9, we confirmed that instar-specific responses towards its cognate ligands rely on the expression of SlitOR40. Conclusion Our results provide evidence that larvae of S. littoralis change their peripheral olfactory system during development. Furthermore, our data demonstrate an unprecedented instar-specific behavioral plasticity mediated by an OR, and knocking out this OR disrupts larval behavioral plasticity. The ecological relevance of such behavioral plasticity for S. littoralis remains to be elucidated, but our results demonstrate an olfactory mechanism underlying this plasticity in foraging behavior during larval development.

De Novo Genome Assembly of Chinese Plateau Honeybee Unravels Intraspecies Genetic Diversity in the Eastern Honeybee, Apis cerana

Apis cerana abansis, widely distributed in the southeastern margin of the Qinghai-Tibet Plateau, is considered an excellent model to study the phenotype and genetic variation for highland adaptation of Asian honeybee. Herein, we assembled and annotated the chromosome-scale assembly genome of A. cerana abansis with the help of PacBio, Illumina and Hi-C sequencing technologies in order to identify the genome differences between the A. cerana abansis and the published genomes of different A. cerana strains. The sequencing methods, assembly and annotation strategies of A. cerana abansis were more comprehensive than previously published A. cerana genomes. Then, the intraspecific genetic diversity of A. cerana was revealed at the genomic level. We re-identified the repeat content in the genome of A. cerana abansis, as well as the other three A. cerana strains. The chemosensory and immune-related proteins in different A. cerana strains were carefully re-identified, so that 132 odorant receptor subfamilies, 12 gustatory receptor subfamilies and 22 immune-related pathways were found. We also discovered that, compared with other published genomes, the A. ceranaabansis lost the largest number of chemoreceptors compared to other strains, and hypothesized that gene loss/gain might help different A. cerana strains to adapt to their respective environments. Our work contains more complete and precise assembly and annotation results for the A. cerana genome, thus providing a resource for subsequent in-depth related studies.

Odorant receptor copy number change, co-expression, and positive selection establish peripheral coding differences between fly species

Animals sample their chemical environment using sensory neurons that express diverse chemosensory receptors, which trigger responses when they bind environmental molecules. In addition to modifications in the ligand binding properties of receptors, chemosensory receptor evolution is characterized by copy number changes, often resulting in large gene family size differences between species. Though chemosensory receptor expansions and contractions are frequently described, it is unknown how this is accompanied by changes in the neural circuitry in which they are expressed. Among Drosophila's chemosensory receptor families, the Odorant receptors (Ors) are ideal for addressing this question because, other than an essential co-receptor (Orco), a large majority of Ors are uniquely expressed in single olfactory sensory neuron (OSN) populations. Between-species changes in Or copy number, therefore, may indicate diversification or reduction of peripheral sensory neuron populations. To test this possibility, we focused on a rapidly duplicated/deleted Or subfamily - named Or67a - within Drosophila melanogaster and its most closely-related sister species (D. simulans, D. sechellia, and D. mauritiana). Evolutionary genetic analyses and in vivo physiological assays demonstrate that the common ancestor of these four species possessed three Or67a paralogs that had already diverged adaptively in their odor-evoked responses. Following the group's speciation events, two Or67a paralogs were independently lost in D. melanogaster and D. sechellia, with positive selection continuing to act on the intact genes. Instead of the expected singular expression of each of the functionally diverged Ors in different neurons, we found that the three D. simulans Or67a paralogs are co-expressed in the same cells. Thus, while neuroanatomy is conserved between these species, independent selection on co-expressed receptors has contributed to species-specific peripheral coding of olfactory information. This work reveals a model of adaptive change previously not considered for olfactory evolution and raises the possibility that similar processes may be operating among the largely uninvestigated cases of Or co-expression.

Genetic and functional odorant receptor variation in the Homo lineage

The largest and rapidly evolving gene family of odorant receptors detect odors to variable degrees due to amino acid sequence and protein structure. Hybridization between humans, Neandertals, and Denisovans implies shared behavior1,2, although some speculate that Neandertals were poor smellers 3,4. We identified genetic and functional variation in humans and extinct lineages in 30 receptors with known function. We show that structural changes in receptor proteins altered odor sensitivity not specificity, indicating a common repertoire across lineages. In humans, variation in receptors may change odor perception or induce odor-specific anosmia 5,6. Variation in sensitivity may reflect local adaptations (e.g., Denisovan sensitivity to honey, Neandertals sensitivity to grass and sulphur). Extinct human lineages had highly conserved receptor genes and proteins. We observe a similar pattern in the Neandertal OR5P3 variant, which produced no response to ∼350 odors. Our data suggest that receptor structure was highly conserved in our closest relatives, but not in living humans. The diversity of geographic adaptations in humans may have produced greater functional variation, increasing our olfactory repertoire and expanding our adaptive capacity 5. Our results provide insight into odorant receptor function and shed light on the olfactory ecology of ancient humans and their extinct relatives. By studying the function of ancient odorant receptor genes, we have been able to get a glimpse of the sensory world of our extinct ancestors and relatives, with some of the variants giving specific insights into potential adaptations shown by these long-dead populations. The functional variability we have identified in the molecular structure of the odorant receptor proteins will aid in the more general problem of understanding the function of odorant receptor proteins and the neurons they are carried by, opening the road to linking receptor function to perception.