Identification of Chemosensory Genes Based on the Transcriptomic Analysis of Six Different Chemosensory Organs in Spodoptera exigua

Abstract

Insects have a complex chemosensory system that accurately perceives external chemicals and plays a pivotal role in many insect life activities. Thus, the study of the chemosensory mechanism has become an important research topic in entomology. Spodoptera exigua Hübner (Lepidoptera: Noctuidae) is a major agricultural polyphagous pest that causes significant agricultural economic losses worldwide. However, except for a few genes that have been discovered, its olfactory and gustatory mechanisms remain uncertain. In the present study, we acquired 144,479 unigenes of S. exigua by assembling 65.81 giga base reads from 6 chemosensory organs (female and male antennae, female and male proboscises, and female and male labial palps), and identified many differentially expressed genes in the gustatory and olfactory organs. Analysis of the transcriptome data obtained 159 putative chemosensory genes, including 24 odorant binding proteins (OBPs; 3 were new), 19 chemosensory proteins (4 were new), 64 odorant receptors (57 were new), 22 ionotropic receptors (16 were new), and 30 new gustatory receptors. Phylogenetic analyses of all genes and SexiGRs expression patterns using quantitative real-time polymerase chain reactions were investigated. Our results found that several of these genes had differential expression features in the olfactory organs compared to the gustatory organs that might play crucial roles in the chemosensory system of S. exigua, and could be utilized as targets for future functional studies to assist in the interpretation of the molecular mechanism of the system. They could also be used for developing novel behavioral disturbance agents to control the population of the moths in the future.

Identification and expression profiles of candidate chemosensory receptors in Histia rhodope (Lepidoptera: Zygaenidae)

“…In the present study, we identified 45 ORs, 9 IRs, 8 GRs and 2 SNMPs from our previous H. rhodope transcriptomic data ( Yang et al, 2020 ). The number of chemoreceptor genes in H. rhodope was less compared to previously reported numbers in other nocturnal lepidopteran species, such as 62 ORs, 20 IRs and 16 GRs in Mythimna separata ( Du et al, 2018 ), 64 ORs, 22 IRs and 30 GRs in Spodoptera exigua ( Zhang et al, 2018 ), 60 ORs, 21 IRs and 197 GRs in H. armigera ( Liu et al, 2014 ; Xu et al, 2016 ), 60 ORs, 17 IRs and 17 GRs in S. littoralis ( Walker III et al, 2019 ) and 58 ORs, 21 IRs and 22 GRs in C. pomonella ( Walker III et al, 2016 ). Previous studies reported that different chemosensory behavior ( Zhang et al, 2017 ), life stage ( He et al, 2017 ), ecological niche breadth ( Gouin et al, 2017 ), phenotype ( Purandare & Brisson, 2020 ), mating status ( Jin et al, 2017 ), circadian rhythm ( Gadenne, Barrozo & Anton, 2016 ) and feeding trait ( Taparia, Ignell & Hill, 2017 ) influence the variation in chemosensory gene number.…”

Coupling transcriptomics and behaviour to unveil the olfactory system ofSpodoptera exigualarvae

“…In contrast, the molecular and physiological mechanisms that underlie olfactory behaviours in larvae are poorly understood and only few reports have described the chemosensory gene set expressed at the larval stage (Chang et al, 2017;Di et al, 2017;McCormick et al, 2017;Poivet et al, 2013;Tanaka et al, 2009;Walker et al, 2016) compared to the plethora of adult transcriptomes available (Montagné et al, 2015). Here, we identified chemosensory-related genes expressed in S. exigua larval heads using RNA-seq and RT-PCR data, expanding previous datasets built from adult data (Du et al, 2018;Zhang et al, 2018). We also developed a method to analyse S.…”

“…( Supplementary Figure 4). Two of the transcripts described by Zhang et al (2018) (OBP25 and OBPN-3) were not identified in our transcriptome. Compared to Du et al (2018), our annotation missed 19 putative OBPs.…”

“…Thus, the final dataset contains a non-redundant list of putatively unique transcripts, which likely correspond to unique genes, although we cannot exclude that some of them might be allelic variants of the same gene. Maximum-likelihood (ML) trees were built with protein sequences annotated from S. frugiperda (Gouin et al, 2017), S. litura and B. mori genomes (Forêt et al, 2007;Tanaka et al, 2009;van Schooten et al, 2016;Vogt et al, 2015;Wanner and Robertson, 2008), as well as putative proteins deduced from S. littoralis (Walker et al, 2019), S. litura (Gu et al, 2015), Helicoverpa armigera, H. assulta (Chang et al, 2017) and previous S. exigua transcriptomes (Du et al, 2018;Zhang et al, 2018). Trees were built using RAxML (Stamatakis, 2014) and amino acid MUSCLE alignments (Edgar, 2004) generated by MEGAX (Kumar et al, 2018).…”

“…Five ORs have not been previous reported by any previous study (SexiOR46, SexiOR54, SexiOR56, SexiOR69 and SexiOr40b) (SupplementaryTable 2).All S. exigua ORs (SexiORs) have a one-to-one ortholog relationship with S. frugiperdaORs except SexiOR40b and SexiOR40c that might represent OR40 lineage-specific duplications in S. exigua, although we cannot exclude they are transcriptional isoforms of the same gene(Figure 2). Our annotation effort missed three incomplete candidate SexiORs described byZhang et al (2018) (namely OR8, OR56, and OR59 according to Zhang's nomenclature). likelihood (ML) tree built with protein sequences annotated from S. frugiperda(Gouin et al, 2017) and B. mori genomes(Tanaka et al, 2009) as well as putative proteins annotated from S. littoralis transcriptome(Walker et al, 2019).…”