Abstract

Neuropeptides are the most abundant and diverse signal molecules in insects. They act as neurohormones and neuromodulators to regulate the physiology and behavior of insects. The majority of neuropeptides initiate downstream signaling pathways through binding to G protein-coupled receptors (GPCRs) on the cell surface. In this study, RNA-seq technology and bioinformatics were used to search for genes encoding neuropeptides and their GPCRs in the cowpea aphid Aphis craccivora. And the expression of these genes at different developmental stages of A. craccivora was analyzed by quantitative real-time PCR (qRT-PCR). A total of 40 candidate genes encoding neuropeptide precursors were identified from the transcriptome data, which is roughly equivalent to the number of neuropeptide genes that have been reported in other insects. On this basis, software analysis combined with homologous prediction estimated that there could be more than 60 mature neuropeptides with biological activity. In addition, 46 neuropeptide GPCRs were obtained, of which 40 belong to rhodopsin-like receptors (A-family GPCRs), including 21 families of neuropeptide receptors and 7 orphan receptors, and 6 belong to secretin-like receptors (B-family GPCRs), including receptors for diuretic hormone 31, diuretic hormone 44 and pigment-dispersing factor (PDF). Compared with holometabolous insects such as Drosophila melanogaster, the coding genes for sulfakinin, corazonin, arginine vasopressin-like peptide (AVLP), and trissin and the corresponding receptors were not found in A. craccivora. It is speculated that A. craccivora likely lacks the above neuropeptide signaling pathways, which is consistent with Acyrthosiphon pisum and that the loss of these pathways may be a common feature of aphids. In addition, expression profiling revealed neuropeptide genes and their GPCR genes that are differentially expressed at different developmental stages and in different wing morphs. This study will help to deepen our understanding of the neuropeptide signaling systems in aphids, thus laying the foundation for the development of new methods for aphid control targeting these signaling systems.

Highlights

  • Insect neuropeptides are trace polypeptides produced by neurosecretory glands or neurosecretory cells in insects [1]

  • Based on RNA-seq technology, we identified a large number of genes encoding neuropeptides and their G protein-coupled receptors (GPCRs) from A. craccivora in this study

  • The sequenced samples probably did not cover all stages of the A. craccivora life cycle, and some genes may not have been expressed in these measured samples; in other cases, some genes are expressed at low abundance in certain tissues or at certain developmental stages and the transcripts would be further diluted in the mixed sample

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Summary

Introduction

Insect neuropeptides are trace polypeptides produced by neurosecretory glands or neurosecretory cells in insects [1]. They are the most abundant and diverse signal molecules and play important regulatory roles in the physiology and behavior in insects such as the growth, development, metabolism, reproduction, and feeding of insects [2]. Insect GPCRs have been proposed to be used as potential targets to explore new insecticides or behavioral regulators, opening up new ways for the safe control of pests [4] By targeting neuropeptide GPCRs, future insecticides or behavioral regulators can prevent or over-stimulate the normal activity of these proteins, producing a lethal or deleterious effect on pests. Aphids are model organisms for studying phenotypic plasticity, insect-plant interactions, insect-plant-virus interactions and endosymbionts and have attracted much attention from researchers [5]

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