Identification of Chemosensory Genes Based on the Antennal Transcriptomic Analysis of Plagiodera versicolora

Insects can sense surrounding chemical signals by their accurate chemosensory systems. This system plays a vital role in the life history of insects. Several gene families participate in chemosensory processes, including odorant receptors (ORs), ionotropic receptors (IRs), gustatory receptors (GRs), chemosensory proteins (CSPs), odorant binding proteins (OBPs), and sensory neuron membrane proteins (SNMPs). Plagiodera versicolora (Coleoptera: Chrysomelidae), is a leaf-eating forest pest found in salicaceous trees worldwide. In this study, a transcriptome analysis of male and female adult antennae in P. versicolora individuals was conducted, which identified a total of 98 candidate chemosensory genes including 40 ORs, 7 IRs, 13 GRs, 10 CSPs, 24 OBPs, and 4 SNMPs. Subsequently, the tissue expression profiles of 15 P. versicolora OBPs (PverOBPs) and 39 ORs (PverORs) were conducted by quantitative real-time PCR. The data showed that almost all PverOBPs and PverORs were highly expressed in the male and female antennae. In addition, several OBPs and ORs (PverOBP10, PverOBP12, PverOBP18, PverOR24, and PverOR35) had higher expression levels in female antennae than those in the male antennae, indicating that these genes may be taking part in some female-specific behaviors, such as find mates, oviposition site, etc. This study deeply promotes further understanding of the chemosensory system and functional studies of the chemoreception genes in P. versicolora.

Mosquito Host-Seeking Diel Rhythm and Chemosensory Gene Expression is Affected by Age and Plasmodium Stages

Malaria parasites can affect vector-related behaviours, increasing transmission success. Using Anopheles gambiae and Plasmodium falciparum, we consider the effect of interaction between infection stage and vector age on diel locomotion in response to human odour and the expression of antennal chemosensory genes. We demonstrate age-dependent behavioural diel compartmentalisation by uninfected females. Infection disrupts overall and diel activity patterns compared with age-matched controls. Mosquitoes carrying transmissible sporozoites are more active, shifting activity periods to coincide with human host availability, in response to human odour. Older, uninfected females reduce activity during their peak host-seeking period in response to human odour. Age- and infection stage-specific changes in odour-mediated locomotion coincide with altered transcript abundance of select chemosensory genes providing a possible molecular mechanism regulating the behaviour. Our results support the hypothesis that vector-related behaviours of female mosquitoes are altered by infection stage and further modulated by the age of the vector, and have important implications for malaria transmission and disease dynamics.

Transcriptome Analysis and Characterization of Chemosensory Genes in the Forest Pest, Dioryctria abietella (Lepidoptera: Pyralidae)

In Lepidoptera, RNA sequencing has become a useful tool in identifying chemosensory genes from antennal transcriptomes, but little attention is paid to non-antennal tissues. Though the antennae are primarily responsible for olfaction, studies have found that a certain number of chemosensory genes are exclusively or highly expressed in the non-antennal tissues, such as proboscises, legs and abdomens. In this study, we report a global transcriptome of 16 tissues from Dioryctria abietella, including chemosensory and non-chemosensory tissues. Through Illumina sequencing, totally 952,658,466 clean reads were generated, summing to 142.90 gigabases of data. Based on the transcriptome, 235 chemosensory-related genes were identified, comprising 42 odorant binding proteins (OBPs), 23 chemosensory proteins (CSPs), 75 odorant receptors (ORs), 62 gustatory receptors (GRs), 30 ionotropic receptors (IRs), and 3 sensory neuron membrane proteins (SNMPs). Compared to a previous study in this species, 140 novel genes were found. A transcriptome-wide analysis combined with PCR results revealed that except for GRs, the majority of other five chemosensory gene families in Lepidoptera were expressed in the antennae, including 160 chemosensory genes in D. abietella. Using phylogenetic and expression profiling analyses, members of the six chemosensory gene repertoires were characterized, in which 11 DabiORs were candidates for detecting female sex pheromones in D. abietella, and DabiOR23 may be involved in the sensing of plant-derived phenylacetaldehyde. Intriguingly, more than half of the genes were detected in the proboscises, and one fourth of the genes were found to have the expression in the legs. Our study not only greatly extends and improves the description of chemosensory genes in D. abietella, but also identifies potential molecular targets involved in olfaction, gustation and non-chemosensory functions for control of this pest.

A Genomic Survey of Mayetiola destructor Mobilome Provides New Insights into the Evolutionary History of Transposable Elements in the Cecidomyiid Midges

The availability of the Whole-Genome Sequence of the wheat pest Mayetiola destructor offers the opportunity to investigate the Transposable Elements (TEs) content and their relationship with the genes involved in the insect virulence. In this study, de novo annotation carried out using REPET pipeline showed that TEs occupy approximately 16% of the genome and are represented by 1038 lineages. Class II elements were the most frequent and most TEs were inactive due to the deletions they have accumulated. The analyses of TEs ages revealed a first burst at 20% of divergence from present that mobilized many TE families including mostly Tc1/mariner and Gypsy superfamilies and a second burst at 2% of divergence, which involved mainly the class II elements suggesting new TEs invasions. Additionally, 86 TEs insertions involving recently transposed elements were identified. Among them, several MITEs and Gypsy retrotransposons were inserted in the vicinity of SSGP and chemosensory genes. The findings represent a valuable resource for more in-depth investigation of the TE impact onto M. destructor genome and their possible influence on the expression of the virulence and chemosensory genes and consequently the behavior of this pest towards its host plants.

Identification and analysis of chemosensory genes encoding odorant-binding proteins, chemosensory proteins and sensory neuron membrane proteins in the antennae of Lissorhoptrus oryzophilus

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is a destructive pest that causes damage to rice crops worldwide. The olfactory system is critical for host or mate location by weevils, but only limited information about the molecular mechanism of olfaction-related behaviour has been reported in this insect. In this study, we conducted SMRT-seq transcriptome analysis and obtained 54,378 transcripts, 38,706 of which were annotated. Based on these annotations, we identified 40 candidate chemosensory genes, including 31 odorant-binding proteins (OBPs), six chemosensory proteins (CSPs) and three sensory neuron membrane proteins (SNMPs). Phylogenetic analysis showed that LoryOBPs, LoryCSPs and LorySNMPs were distributed in various clades. The results of tissue expression patterns indicated that LoryOBPs were highly abundant in the antennae, whereas LoryCSPs were highly abundant not only in the antennae but also in the abdomen, head and wings. Our findings substantially expand the gene database of L. oryzophilus and may serve as a basis for identifying novel targets to disrupt key olfactory genes, potentially providing an eco-friendly strategy to control this pest in the future.

Identification and Expression Profile of Chemosensory Genes in the Small Hive Beetle Aethina tumida

Aethina tumida is a parasite and predator of honeybee causing severe loss to the bee industry. No effective and environmentally friendly methods are available to control this pest at present. Chemosensory genes play key roles in insect behavior which can potentially be used as targets for developing environmentally friendly pest control agents. In this study, the putative chemosensory genes in antennae and forelegs of A. tumida involved in olfaction or contact chemical communication of adults were investigated using RNA transcriptome sequencing and PCR methods. Based on transcriptomic data, unigenes encoding 38 odorant receptors (ORs), 24 ionotropic receptors (IRs), 14 gustatory receptors (GRs), 3 sensory neuron membrane proteins (SNMPs), 29 odorant binding proteins (OBPs), and 22 chemosensory proteins (CSPs) were identified. The analyses of tissue expression profiles revealed that genes encoding 38 ORs, 13 antennal IRs, 11 GRs, 1 SNMP, 24 OBPs, and 12 CSPs were predominately expressed in antennae. No significant differences in expression levels of these genes were found between males and females. Genes encoding 5 non-NMDA iGluRs, 3 GRs, 2 SNMPs, 5 OBPs, and 12 CSPs were predominately expressed in forelegs. RT-PCR assays for SNMPs, OBPs and CSPs further revealed that 3 OBPs (AtumOBP3, 26 and 28) and 3 CSPs (AtumCSP7, 8 and 21) were highly expressed in antennae. Our results enrich the gene inventory of A. tumida and facilitate the discovery of potential novel targets for developing new pest control measures.

Description of Chemosensory Genes in Unexplored Tissues of the Moth Spodoptera littoralis

Illumina-based transcriptome sequencing of chemosensory organs has become a standard in deciphering the molecular bases of chemical senses in insects, especially in non-model species. A plethora of antennal transcriptomes is now available in the literature, describing large sets of chemosensory receptors and binding proteins in a diversity of species. However, little is still known on other organs such as mouthparts, legs and ovipositors, which are also known to carry chemosensory sensilla. This is the case of the noctuid Spodoptera littoralis, which has been established as a model insect species in molecular chemical ecology thanks to the description of many—but not all—chemosensory genes. To fulfill this gap, we present here an unprecedented transcriptomic survey of chemosensory tissues in this species. RNAseq from male and female proboscis, labial palps, legs and female ovipositors allowed us to annotate 115 putative chemosensory gene transcripts, including 30 novel genes in this species. Especially, we doubled the number of candidate gustatory receptor transcripts described in this species. We also evidenced ectopic expression of many chemosensory genes. Remarkably, one third of the odorant receptors were found to be expressed in the proboscis. With a total of 196 non-overlapping chemosensory genes annotated, the S. littoralis repertoire is one of the most complete in Lepidoptera. We further evaluated the expression of transcripts between males and females, pinpointing sex-specific transcripts. We identified five female-specific transcripts, including one odorant receptor, one gustatory receptor, one ionotropic receptor and one odorant-binding protein, and one male-specific gustatory receptor. Such sex-biased expression suggests that these transcripts participate in sex-specific behaviors, such as host choice for oviposition in females and/or mating partner recognition in both sexes.