Neonicotinoid binding, toxicity and expression of nicotinic acetylcholine receptor subunits in the aphid Acyrthosiphon pisum

Neonicotinoid insecticides act on nicotinic acetylcholine receptor and are particularly effective against sucking pests. They are widely used in crops protection to fight against aphids, which cause severe damage. In the present study we evaluated the susceptibility of the pea aphid Acyrthosiphon pisum to the commonly used neonicotinoid insecticides imidacloprid (IMI), thiamethoxam (TMX) and clothianidin (CLT). Binding studies on aphid membrane preparations revealed the existence of high and low-affinity binding sites for [3H]-IMI (Kd of 0.16 ± 0.04 nM and 41.7 ± 5.9 nM) and for the nicotinic antagonist [125I]-α-bungarotoxin (Kd of 0.008 ± 0.002 nM and 1.135 ± 0.213 nM). Competitive binding experiments demonstrated that TMX displayed a higher affinity than IMI for [125I]-α-bungarotoxin binding sites while CLT affinity was similar for both [125I]-α-bungarotoxin and [3H]-IMI binding sites. Interestingly, toxicological studies revealed that at 48 h, IMI (LC50 = 0.038 µg/ml) and TMX (LC50 = 0.034 µg/ml) were more toxic than CLT (LC50 = 0.118 µg/ml). The effect of TMX could be associated to its metabolite CLT as demonstrated by HPLC/MS analysis. In addition, we found that aphid larvae treated either with IMI, TMX or CLT showed a strong variation of nAChR subunit expression. Using semi-quantitative PCR experiments, we detected for all insecticides an increase of Apisumα10 and Apisumβ1 expressions levels, whereas Apisumβ2 expression decreased. Moreover, some other receptor subunits seemed to be differently regulated according to the insecticide used. Finally, we also demonstrated that nAChR subunit expression differed during pea aphid development. Altogether these results highlight species specificity that should be taken into account in pest management strategies

Comparison of Gene Repertoires and Patterns of Evolutionary Rates in Eight Aphid Species That Differ by Reproductive Mode

In theory, the loss of sexual reproduction is expected to result in the accumulation of deleterious mutations. In aphids, two main types of life cycle, cyclic and obligate parthenogenesis, represent respectively “sexual” and “asexual” reproductive modes. We used the complete pea aphid genome and previously published expressed sequence tags (ESTs) from two other aphid species. In addition, we obtained 100,000 new ESTs from five more species. The final set comprised four sexual and four asexual aphid species and served to test the influence of the reproductive mode on the evolutionary rates of genes. We reconstructed coding sequences from ESTs and annotated these genes, discovering a novel peptide gene family that appears to be among the most highly expressed transcripts from several aphid species. From 203 genes found to be 1:1 orthologs among the eight species considered, we established a species tree that partly conflicted with taxonomy (for Myzus ascalonicus). We then used this topology to evaluate the dynamics of evolutionary rates and mutation accumulation in the four sexual and four asexual taxa. No significant increase of the nonsynonymous to synonymous ratio or of nonsynonymous mutation numbers was found in any of the four branches for asexual taxa. We however found a significant increase of the synonymous rate in the branch leading to the asexual species Rhopalosiphum maidis, which could be due to a change in the mutation rate or to an increased number of generations implied by its change of life cycle

Transcriptomic and proteomic analyses of seasonal photoperiodism in the pea aphid

<p>Abstract</p> <p>Background</p> <p>Aphid adaptation to harsh winter conditions is illustrated by an alternation of their reproductive mode. Aphids detect photoperiod shortening by sensing the length of the night and switch from viviparous parthenogenesis in spring and summer, to oviparous sexual reproduction in autumn. The photoperiodic signal is transduced from the head to the reproductive tract to change the fate of the future oocytes from mitotic diploid embryogenesis to haploid formation of gametes. This process takes place in three consecutive generations due to viviparous parthenogenesis. To understand the molecular basis of the switch in the reproductive mode, transcriptomic and proteomic approaches were used to detect significantly regulated transcripts and polypeptides in the heads of the pea aphid <it>Acyrthosiphon pisum</it>.</p> <p>Results</p> <p>The transcriptomic profiles of the heads of the first generation were slightly affected by photoperiod shortening. This suggests that trans-generation signalling between the grand-mothers and the viviparous embryos they contain is not essential. By analogy, many of the genes and some of the proteins regulated in the heads of the second generation are implicated in visual functions, photoreception and cuticle structure. The modification of the cuticle could be accompanied by a down-regulation of the <it>N</it>-β-alanyldopamine pathway and desclerotization. In <it>Drosophila</it>, modification of the insulin pathway could cause a decrease of juvenile hormones in short-day reared aphids.</p> <p>Conclusion</p> <p>This work led to the construction of hypotheses for photoperiodic regulation of the switch of the reproductive mode in aphids.</p

Identification de cibles d’insecticides spécifiques du puceron du pois Acyrthosiphon piusm par analyse des relations structure-fonction des récepteurs nicotiniques

Session 1 - Thérapies et résistancesNational audienc

Expansion of the miRNA Pathway in the Hemipteran Insect Acyrthosiphon pisum

The pathways that allow short noncoding RNAs such as the microRNAs (miRNAs) to mediate gene regulation and control critical cellular and developmental processes involve a limited number of key protein components. These proteins are the Dicer-like RNases, double-stranded RNA (dsRNA)-binding proteins, and the Argonaute (AGO) proteins that process stem-loop hairpin transcripts of endogenous genes to generate miRNAs or long dsRNA precursors (either exogenous or endogenous). Comparative genomics studies of metazoans have shown the pathways to be highly conserved overall; the major difference observed is that the vertebrate pathways overlap in sharing a single Dicer (DCR) and AGO proteins, whereas those of insects appear to be parallel, with distinct Dicers and AGOs required for each pathway. The genome of the pea aphid is the first available for a hemipteran insect and discloses an unexpected expansion of the miRNA pathway. It has two copies of the miRNA-specific dicr-1 and ago1 genes and four copies of pasha a cofactor of drosha involved in miRNA biosynthesis. For three of these expansions, we showed that one copy of the genes diverged rapidly and in one case (ago1b) shows signs of positive selection. These expansions occurred concomitantly within a brief evolutionary period. The pea aphid, which reproduces by viviparous parthenogenesis, is able to produce several adapted phenotypes from one single genotype. We show by reverse transcriptase-polymerase chain reaction that all the duplicated copies of the miRNA machinery genes are expressed in the different morphs. Investigating the function of these novel genes offers an exciting new challenge in aphid biology

Functional insights from the GC-poor genomes of two aphid parasitoids, Aphidius ervi and Lysiphlebus fabarum.

Parasitoid wasps have fascinating life cycles and play an important role in trophic networks, yet little is known about their genome content and function. Parasitoids that infect aphids are an important group with the potential for biological control. Their success depends on adapting to develop inside aphids and overcoming both host aphid defenses and their protective endosymbionts. We present the de novo genome assemblies, detailed annotation, and comparative analysis of two closely related parasitoid wasps that target pest aphids: Aphidius ervi and Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae). The genomes are small (139 and 141 Mbp) and the most AT-rich reported thus far for any arthropod (GC content: 25.8 and 23.8%). This nucleotide bias is accompanied by skewed codon usage and is stronger in genes with adult-biased expression. AT-richness may be the consequence of reduced genome size, a near absence of DNA methylation, and energy efficiency. We identify missing desaturase genes, whose absence may underlie mimicry in the cuticular hydrocarbon profile of L. fabarum. We highlight key gene groups including those underlying venom composition, chemosensory perception, and sex determination, as well as potential losses in immune pathway genes. These findings are of fundamental interest for insect evolution and biological control applications. They provide a strong foundation for further functional studies into coevolution between parasitoids and their hosts. Both genomes are available at https://bipaa.genouest.org

Combining Next-Generation Sequencing Strategies for Rapid Molecular Resource Development from an Invasive Aphid Species, Aphis glycines

Aphids are one of the most important insect taxa in terms of ecology, evolutionary biology, genetics and genomics, and interactions with endosymbionts. Additionally, many aphids are serious pest species of agricultural and horticultural plants. Recent genetic and genomic research has expanded molecular resources for many aphid species, including the whole genome sequencing of the pea aphid, Acrythosiphon pisum. However, the invasive soybean aphid, Aphis glycines, lacks in any significant molecular resources.Two next-generation sequencing technologies (Roche-454 and Illumina GA-II) were used in a combined approach to develop both transcriptomic and genomic resources, including expressed genes and molecular markers. Over 278 million bp were sequenced among the two methods, resulting in 19,293 transcripts and 56,688 genomic sequences. From this data set, 635 SNPs and 1,382 microsatellite markers were identified. For each sequencing method, different soybean aphid biotypes were used which revealed potential biotype specific markers. In addition, we uncovered 39,822 bp of sequence that were related to the obligatory endosymbiont, Buchnera aphidicola, as well as sequences that suggest the presence of Hamiltonella defensa, a facultative endosymbiont.Molecular resources for an invasive, non-model aphid species were generated. Additionally, the power of next-generation sequencing to uncover endosymbionts was demonstrated. The resources presented here will complement ongoing molecular studies within the Aphididae, including the pea aphid whole genome, lead to better understanding of aphid adaptation and evolution, and help provide novel targets for soybean aphid control

Genome Sequence of the Pea Aphid Acyrthosiphon pisum

Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetabolous insect provides an outgroup to the multiple published genomes of holometabolous insects. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. Here we highlight findings from whole genome analysis that may be related to these unusual biological features. These findings include discovery of extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, purine salvage, and the entire urea cycle. The pea aphid genome reveals that only a limited number of genes have been acquired from bacteria; thus the reduced gene count of Buchnera does not reflect gene transfer to the host genome. The inventory of metabolic genes in the pea aphid genome suggests that there is extensive metabolite exchange between the aphid and Buchnera, including sharing of amino acid biosynthesis between the aphid and Buchnera. The pea aphid genome provides a foundation for post-genomic studies of fundamental biological questions and applied agricultural problems