Gene knockdown by RNAi in the pea aphid Acyrthosiphon pisum

<p>Abstract</p> <p>Background</p> <p>RNA interference (RNAi) is a powerful method to inhibit gene expression in a sequence specific manner.</p> <p>Results</p> <p>Here, we described the development of RNAi by micro-injection of double-stranded RNA (dsRNA) in the pea aphid <it>Acyrthosiphon pisum</it>. Injection of dsRNA into whole aphid body induced the silencing of two marker genes with different expression patterns: the ubiquitously expressed <it>Ap-crt </it>genes encoding a calreticulin and the gut specific <it>Ap-cath-L </it>gene encoding a cathepsin-L. Time-course analysis of the silencing showed similar temporal patterns for both genes: inhibition started at 1 day after injection, reached its maximum at 5 days and stopped at 7 days. A comparable 40% decrease of gene expression was observed for <it>Ap-crt </it>and <it>Ap-cath-L</it>.</p> <p>Conclusion</p> <p>The pea aphid is the first Hemipteran insect for which genome sequence will be available soon. The gene knockdown technique developed in this study will be an essential post-genomic tool for further investigations in aphidology.</p

Masculinization of the X Chromosome in the Pea Aphid

International audienceEvolutionary theory predicts that sexually antagonistic mutations accumulate differentially on the X chromosome and autosomes in species with an XY sex-determination system, with effects (masculinization or feminization of the X) depending on the dominance of mutations. Organisms with alternative modes of inheritance of sex chromosomes offer interesting opportunities for studying sexual conflicts and their resolution, because expectations for the preferred genomic location of sexually antagonistic alleles may differ from standard systems. Aphids display an XX/X0 system and combine an unusual inheritance of the X chromosome with the alternation of sexual and asexual reproduction. In this study, we first investigated theoretically the accumulation of sexually antagonistic mutations on the aphid X chromosome. Our results show that i) the X is always more favourable to the spread of male-beneficial alleles than autosomes, and should thus be enriched in sexually antagonistic alleles beneficial for males, ii) sexually antagonistic mutations beneficial for asexual females accumulate preferentially on autosomes, iii) in contrast to predictions for standard systems, these qualitative results are not affected by the dominance of mutations. Under the assumption that sex-biased gene expression evolves to solve conflicts raised by the spread of sexually antagonistic alleles, one expects that male-biased genes should be enriched on the X while asexual female-biased genes should be enriched on autosomes. Using gene expression data (RNA-Seq) in males, sexual females and asexual females of the pea aphid, we confirm these theoretical predictions. Although other mechanisms than the resolution of sexual antagonism may lead to sex-biased gene expression, we argue that they could hardly explain the observed difference between X and autosomes. On top of reporting a strong masculinization of the aphid X chromosome, our study highlights the relevance of organisms displaying an alternative mode of sex chromosome inheritance to understanding the forces shaping chromosome evolution

The Genome Sequence of the Grape Phylloxera Provides Insights into the Evolution, Adaptation, and Invasion Routes of an Iconic Pest

Background: Although native to North America, the invasion of the aphid-like grape phylloxera Daktulosphaira vitifoliae across the globe altered the course of grape cultivation. For the past 150 years, viticulture relied on grafting-resistant North American Vitis species as rootstocks, thereby limiting genetic stocks tolerant to other stressors such as pathogens and climate change. Limited understanding of the insect genetics resulted in successive outbreaks across the globe when rootstocks failed. Here we report the 294-Mb genome of D. vitifoliae as a basic tool to understand host plant manipulation, nutritional endosymbiosis, and enhance global viticulture. Results: Using a combination of genome, RNA, and population resequencing, we found grape phylloxera showed high duplication rates since its common ancestor with aphids, but similarity in most metabolic genes, despite lacking obligate nutritional symbioses and feeding from parenchyma. Similarly, no enrichment occurred in development genes in relation to viviparity. However, phylloxera evolved > 2700 unique genes that resemble putative effectors and are active during feeding. Population sequencing revealed the global invasion began from the upper Mississippi River in North America, spread to Europe and from there to the rest of the world. Conclusions: The grape phylloxera genome reveals genetic architecture relative to the evolution of nutritional endosymbiosis, viviparity, and herbivory. The extraordinary expansion in effector genes also suggests novel adaptations to plant feeding and how insects induce complex plant phenotypes, for instance galls. Finally, our understanding of the origin of this invasive species and its genome provide genetics resources to alleviate rootstock bottlenecks restricting the advancement of viticulture

Bases moléculaires du polyphenisme de reproduction chez le puceron du pois Acyrthosiphon pisum : analyse transcriptomique du photopériodisme

Diplôme : Dr. d'UniversitéLes pucerons sont d’importants ravageurs des cultures agronomiques qui se développent par parthénogénèse au printemps et en été. Ce mode de multiplication asexué explique leur importante dynamique démographique et les dégâts causés sur les cultures. Afin de survivre aux conditions environnementales délicates pendant la période hivernale, les pucerons produisent des individus sexués à la fin de l’été, lesquels vont s’accoupler pour produire un œuf résistant au froid. Ce polyphénisme de reproduction est principalement induit par la diminution de la photopériode à la fin de l’été. L’objectif de ce travail de thèse est donc de comprendre les bases génétiques et moléculaires de ce photopériodisme saisonnier chez les pucerons. Pour ce faire, l’approche transcriptomique a été choisie, avec mise au point et utilisation de la technique des puces à ADNc pour identifier des gènes puis des programmes génétiques régulés par la diminution de la photopériode. Différentes séries d’hybridations réalisées au moyen de 2 générations de lames de verres ont permis d’identifier des fonctions cellulaires impliquées dans la régulation du polyphénisme de reproduction. La détection d’une diminution de la photopériode pourrait ainsi impliquer les systèmes visuel et de photoréception. La modification de la structure de la cuticule induite par un changement de photopériode pourrait également constituer une voie de signalisation indiquant à l’insecte la diminution de la longueur du jour. Le système neuro-endocrine assurerait ensuite la transduction du signal photopériodique du cerveau jusqu’aux organes cibles, les ovarioles.Les résultats des analyses transcriptomiques ont également suggéré que les pucerons pourraient percevoir les modifications de la photopériode dès le stade embryonnaire, ce qui a été testé puis confirmé au moyen d’expérimentations biologiques spécifiques. Enfin, la réalisation d’analyses biologiques et transcriptomiques de la réponse du puceron à une diminution de la photopériode en conditions semi-naturelles a permis de confirmer l’implication des fonctions cellulaires détectées comme impliquées dans la régulation du polyphénisme de reproduction en conditions contrôlée

Bases moléculaires du polyphénisme de reproduction chez le puceron du pois Acyrthosiphon pisum (Analyse transcriptomique du photoperiodisme)

RENNES-Agrocampus-CRD (352382323) / SudocSudocFranceF

Identifier différentes morphologies phénotypiques du puceron (ici Acyrthosiphon pisum)

National audienceLe cycle de vie d’Acyrthosiphon pisum montre des individus parthénogénétiques presque toujours aptères au printemps, plusieurs générations asexuées par an, puis des individus sexués à l’automne. Ces changements du mode de reproduction sont conditionnés par la photopériode, laquelle induit des modifications neuro-hormonales et moléculaires, en particulier une sécrétion variable d’hormone juvénile

Mutagenèse dirigée par la système CRISPR-Cas9

National audienc

Small RNAs in angiosperm gametophytes: from epigenetics to gamete development

The established role of various small RNA pathways in the epigenetic regulation of gene expression in the dipolid sporophytic generation of flowering plants contrasts sharply with the lack of knowledge of their role in haploid gametophyte generation. Several recent studies now uncover the operation of multiple small RNA pathways in male and female gametophytes and their essential roles in genome integrity, cell specification, and, most recently, sperm cell function, as described in the May 15, 2010, issue of Genes & Development by Ron and colleagues (pp. 1010–1021)

Genome expression control during the photoperiodic response of aphids

International audienceAphids are major crop pests and show a high level of phenotypic plasticity. They display a seasonal, photoperiodically-controlled polyphenism during their life cycle. In spring and summer, they reproduce efficiently by parthenogenesis. At the end of summer, parthenogenetic individuals detect the transition from short nights to long nights, which initiates the production of males and oviparous females within their offspring. These are the morphs associated with the autumn season. Deciphering the physiological and molecular events associated with this switch in reproductive mode in response to photoperiodic conditions is thus of key interest for understanding and explaining the remarkable capacity of aphids to adapt to fluctuations in their environment. The present review aims to compile earlier physiological studies, focussing on the neuroendocrine control of seasonal photoperiodism, as well as a series of large-scale transcriptomic approaches made possible by the recent development of genomic resources for the model aphid species: the pea aphid Acyrthosiphon pisum. These analyses identify genetic programmes putatively involved in the control of the initial steps of detection and transduction of the photoperiodic signal, as well as in the regulation of the switch between asexual and sexual oogenesis within embryonic ovaries. The contribution of small RNAs pathways (and especially microRNAs) in the post-transcriptional control of gene expression, as well as the role of epigenetic mechanisms in the regulation of genome expression associated with the photoperiodic response, is also summarized

Contribution of Epigenetic Mechanisms in the Regulation of Environmentally-Induced Polyphenism in Insects

International audienceMany insect species display a remarkable ability to produce discrete phenotypes in response to changes in environmental conditions. Such phenotypic plasticity is referred to as polyphenism. Seasonal, dispersal and caste polyphenisms correspond to the most-studied examples that are environmentally-induced in insects. Cues that induce such dramatic phenotypic changes are very diverse, ranging from seasonal cues, habitat quality changes or differential larval nutrition. Once these signals are perceived, they are transduced by the neuroendocrine system towards their target tissues where gene expression reprogramming underlying phenotypic changes occur. Epigenetic mechanisms are key regulators that allow for genome expression plasticity associated with such developmental switches. These mechanisms include DNA methylation, chromatin remodelling and histone post-transcriptional modifications (PTMs) as well as non-coding RNAs and have been studied to various extents in insect polyphenism. Differential patterns of DNA methylation between phenotypes are usually correlated with changes in gene expression and alternative splicing events, especially in the cases of dispersal and caste polyphenism. Combinatorial patterns of histone PTMs provide phenotype-specific epigenomic landscape associated with the expression of specific transcriptional programs, as revealed during caste determination in honeybees and ants. Alternative phenotypes are also usually associated with specific non-coding RNA profiles. This review will provide a summary of the current knowledge of the epigenetic changes associated with polyphenism in insects and highlights the potential for these mechanisms to be key regulators of developmental transitions triggered by environmental cues