Identification and comparative expression profiles of chemosensory genes in major chemoreception organs of a notorious pests, Laodelphax striatellus

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Highlights

  • We identified 15 OBPs, 12 CSPs, 7 SNMPs and 95 ORs in Laodelphax striatellus.

  • Six LstrOBPs, four LstrSNMP and most LstrORs were highly expressed in antennae.

  • These findings provide information for disrupting the feeding behavior of L. striatellus.

Abstract

The small brown planthopper, Laodelphax striatellus (Stål) (SBPH), is a notorious rice pest in East Asia and damages the host by feeding on the phloem and transmitting virus particles. Although SBPH relies on chemosensory perception for seeking the host, courtship, selecting oviposition sites and spreading virus particles, a systematic study of chemosensory genes in SBPH is lacking. In this study, we identified multi-gene chemosensory families from the transcriptome of SBPH olfactory organs and analyzed their expression patterns in male and female tissues. Among the chemosensory genes, 14 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 7 sensory neuron membrane proteins (SNMPs) and 95 odorant receptors (ORs) were identified and annotated in SBPH olfactory organs. Based on expression profile and phylogenetic analysis, LstrOBP1, 2, 5, 6, 7, 10, LstrSNMP1, and most LstrORs showed an antennae-enriched expression pattern, which suggests an olfactory role for these genes. Relative expression of LstrOBPs was validated by quantitative real-time PCR. Our findings provide the genetic information for disrupting the feeding behavior of SBPH, which is essential for developing eco-friendly pest management technologies.

Introduction

The ability to respond to a wide range of olfactory cues drive insects to seek hosts, mates and spawning sites, which depend on insect chemosensation (Renou and Guerrero, 2000). The semiochemicals from the environment are initially detected by olfactory sensilla on the main periphery, such as the main sensory organ antennae (Morita, 1972). Odorant signals are then processed at the antennal lobes, and conveyed to insect brain. Cascade reactions from sensory organs to the brain result in olfactory signal transduction to electric signals, which eventually modulate insect behavior (Leal, 2013; Pelosi et al., 2014). Interactions between semiochemicals and proteins enable insects to distinguish multiple odorant cues. A number of protein families as active roles in this peripheral process have been identified. These include two classes of carrier proteins: chemosensory proteins (CSPs) and odorant-binding proteins (OBPs), and four classes of membrane proteins: ionotropic (IR), gustatory (GRs), membrane-bound odorant receptors (ORs), and sensory neuron membrane proteins (SNMPs) (Clyne et al., 2000; Benton et al., 2007, Benton et al., 2006; Leal, 2013; Pelosi et al., 2018, Pelosi et al., 2006).

CSPs and OBPs are carriers of odorants and pheromones in insect chemoreception. These are low-molecular weight, soluble proteins excreted by accessory cells that accumulate in the lymph of sensilla (Pelosi et al., 2014). Classic OBPs present a conservative domain formed by six cysteine pairs interlocked disulfide bridges (Leal et al., 1999; Scaloni et al., 1999). Based on structural differences, OBP family members are grouped into minus-C, plus-C and atypical OBPs (Xu et al., 2003; Zhou et al., 2004; Spinelli et al., 2012). Compared to OBPs, CSPs are smaller and usually share four conserved cysteines that are connected by two disulfide bridges (Campanacci et al., 2003). Both OBPs and CSPs participate in insect olfaction (Jacquin-Joly et al., 2001; Briand et al., 2002), and CSPs also function in other physiological processes including regeneration, development, and pesticide resistance (He et al., 2017; Zhang et al., 2017, Zhang et al., 2016; Mei et al., 2018).

Sensory neuron membrane proteins (SNMPs) were initially identified in the membrane of odorant sensory neurons (OSNs) of Lepidoptera where they participated in odorant perception (Rogers et al., 1997, Rogers et al., 2001). SNMPs possess two transmembrane domains (TMDs) and are subdivided into two groups, SNMP1 and SNMP2 (Forstner et al., 2008; Nichols and Vogt, 2008). Insect SNMPs are primarily involved in the perception of pheromones (Rogers et al., 2001, Rogers et al., 1997; Benton et al., 2007).

Insect ORs are transmembrane proteins that localize to the dendritic membrane of OSNs (Hallem et al., 2006; Eyun et al., 2017). Typical ORs contain diverse, seven-transmembrane domains and a reversed membrane topology (Mombaerts, 1999). After stimulation by chemical odors, heterodimeric ion channels are formed by activated ORs and a common subfamily of ORs, the odorant receptor co-receptor (Orco); this triggers the odorant signal transduction cascade (Benton et al., 2006). OR genes exhibit little sequence identity within insect species, while Orco sequences are highly-conserved (Sato et al., 2008; Leal, 2013).

Laodelphax striatellus (Stål), the small brown planthopper (SBPH), is a notorious rice pest in East Asia (Heong et al., 2015). SBPH can cause enormous economic losses to rice production by feeding on the phloem and by transmitting plant viruses, including rice black-streaked dwarf virus (RBSDV) and rice stripe virus (RSV) (Wei and Li, 2016). Extracts from rice plants attract SBPHs, indicating that the olfaction system plays key roles in SBPH behavior (Obata et al., 1983). Genomic and transcriptome analysis recently identified 16 OBPs, 12 CSPs, and 37 ORs in intact bodies of SBPH (He et al., 2019, He et al., 2018). The number of chemosensory genes in SBPH was far fewer than the number reported in other insect, such as 116 chemosensory genes in Chilo suppressalis, 130 chemosensory genes in Mythimna separate and 118 chemosensory genes in Plutella xyllostella (Cao et al., 2014; Chang et al., 2017; Yang et al., 2017). Furthermore, there are fewer studies documenting SNMPs in L. striatellus. Thus, to better understand the SBPH olfactory system for developing eco-friendly control strategies, we analyzed samples of the primary olfactory organs, along with legs and heads of both SBPH sexes. Moreover, we identified novel chemosensory genes in SBPH, investigated phylogenetic relationships and motifs, and profiled transcript accumulation of chemosensory genes in three important olfactory organs.

Section snippets

Insects

L. striatellus was collected from Jiangsu province, China, and reared on rice cv. Wuyujing 3 at 25 ± 1 °C, 80 ± 5% RH and a 13-h light:11-h dark photoperiod.

Preparation of L. striatellus tissues

More than 3000 SBPH female or male adults were collected. All antennae, heads (without antennae) and legs of these adults were dissected and stored in ice-cold RNAlater Reagent (Ambion, Austin, TX, USA) at −80 °C for each RNA libraries.

Illumina sequencing

Total RNA was extracted from insect samples using Trizol as recommended by the manufacturer (Ambion,

Transcriptome sequencing and assembly of SBPH tissues

The transcriptomes of male and female SBPH antennae, heads and legs were sequenced using the Illumina HiSeq™ 2000 platform. Approximately 53.7, 57.2, 61.2, 63.9, 52.2, and 58.3 million raw reads were obtained from six cDNA libraries of male and female antennae, legs, and heads. After filtering raw data, 53.4, 56.8, 61.0, 63.5, 51.9, and 58.1 million respective clean-reads were generated (Table S2). Over 61.4% paired-end clean reads of each transcriptome were mapped to the SBPH genome (Table

Discussion

In the current study, transcriptomes of SBPH antennae, heads and legs from male and female adults were sequenced. The tissue-specific SBPH transcriptomes generated in this study contained 14 OBPs, 12 CSPs (two novel CSPs), seven novel SNMPs and 95 ORs (58 novel ORs). Also belong to Delphacidae, other two rice planthoppers, the white-backed planthopper (WBPH) Sogatella furcifera and the brown planthopper (BPH) Nilaparvata lugens, are notorious rice pests. The SBPH and the WBPH are oligophagous

Data deposition

Illumina sequencing reads from these transcriptomes were submitted to the NCBI Sequence Read Archive under accession number PRJNA589749.

Declaration of competing interest

The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Acknowledgement

This research was financially supported by National Natural Science Foundation of China (No. 31801732 & 31701786), National Key Research Program (2018YFD0300804), and the Key Research Program of Jiangsu Province (BE2018355), Jiangsu Agricultural Scientific Self-innovation Fund (No. CX[18]3057).

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