N. Prunier-Leterme

Bio: N. Prunier-Leterme is an academic researcher from Institut national de la recherche agronomique. The author has contributed to research in topics: Acyrthosiphon pisum & Autosome. The author has an hindex of 16, co-authored 20 publications receiving 1217 citations. Previous affiliations of N. Prunier-Leterme include École nationale supérieure agronomique de Rennes & University of Rennes.

Host–based divergence in populations of the pea aphid: insights from nuclear markers and the prevalence of facultative symbionts

Abstract: In North America, the pea aphid Acyrthosiphon pisum encompasses ecologically and genetically distinct host races that offer an ideal biological system for studies on sympatric speciation. In addition to its obligate symbiont Buchnera, pea aphids harbour several facultative and phylogenetically distant symbionts. We explored the relationships between host races of A. pisum and their symbiotic microbiota to gain insights into the historical process of ecological specialization and symbiotic acquisition in this aphid. We used allozyme and microsatellite markers to analyse the extent of genetic differentiation between populations of A. pisum on pea, alfalfa and clover in France. In parallel, we examined: (i) the distribution of four facultative symbionts; and (ii) the genetic variation in the Buchnera genome across host-associated populations of A. pisum. Our study clearly demonstrates that populations of A. pisum on pea, clover and alfalfa in France are genetically divergent, which indicates that they constitute distinct host races. We also found a very strong association between host races of A. pisum and their symbiotic microbiota. We stress the need for phylogeographic studies to shed light on the process of host-race formation and acquisition of facultative symbionts in A. pisum. We also question the effects of these symbionts on aphid host fitness, including their role in adaptation to a host plant.

Cross-species amplification of microsatellite loci in aphids: assessment and application

Abstract: Despite the relative ease of isolating microsatellites, their development still requires substantial inputs of time, money and expertise For this reason there is considerable interest in using existing microsatellites on species from which markers were not cloned We tested cross-species amplification of 48 existing aphid loci in species of the following genera: Aphidinae: Aphidini: Aphis and Rhopalosiphum ; Aphidinae: Macrosiphini: Acyrthosiphum , Brevicoryne , Diuraphis , Illinoia , Macrosiphoniella , Macrosiphum , Metopeurum , Metapolophium , Myzus , Phorodon , Sitobion and Uroleucon and Neuquenaphidinae: Neuquenaphis Our results show cross-species application of known microsatellite loci is a highly promising source of codominant markers for population genetic and evolutionary studies in aphids

Large-scale gene discovery in the pea aphid Acyrthosiphon pisum (Hemiptera)

Abstract: Aphids are the leading pests in agricultural crops. A large-scale sequencing of 40,904 ESTs from the pea aphid Acyrthosiphon pisum was carried out to define a catalog of 12,082 unique transcripts. A strong AT bias was found, indicating a compositional shift between Drosophila melanogaster and A. pisum. An in silico profiling analysis characterized 135 transcripts specific to pea-aphid tissues (relating to bacteriocytes and parthenogenetic embryos). This project is the first to address the genetics of the Hemiptera and of a hemimetabolous insect.

Phylogenetic evidence for hybrid origins of asexual lineages in an aphid species.

Abstract: Understanding the mode of origin of asexuality is central to ongoing debates concerning the evolution and maintenance of sexual reproduction in eukaryotes. This is because it has profound consequences for patterns of genetic diversity and ecological adaptability of asexual lineages, hence on the outcome of competition with sexual relatives both in short and longer terms. Among the possible routes to asexuality, hybridization is a very common mechanism in animals and plants. Aphids present frequent transitions from their ancestral reproductive mode (cyclical parthe- nogenesis) to permanent asexuality, but the mode of origin of asexual lineages is generally not known because it has never been thoroughly investigated with appropriate molecular tools. Rhopalosiphum padi is an aphid species with coexisting sexual (cyclically parthenogenetic) and asexual (obligately parthenogenetic) lineages that are genetically distinct. Previous studies have shown that asexual lineages of R. padi are heterozygous at most nuclear loci, suggesting either that they have undergone long-term asexuality (under which heterozygosity tends to increase) or that they have hybrid origins. To discriminate between these alternatives, we conducted an extensive molecular survey combining the sequence analysis of alleles of two nuclear DNA markers and mitochondrial DNA haplotypes in sexual and asexual lineages of R. padi. Both nuclear and cytoplasmic markers clearly showed that many asexual lineages have hybrid origins, the first such demonstration in aphids. Our results also indicated that asexuals result from multiple events of hybridization between R. padi and an unknown sibling species, and are of recent origin (contradicting previous estimates that asexual R. padi lineages were of moderate longevity). This study constitutes another example that putatively ancient asexual lineages are actually of much more recent origin than previously thought. It also presents a robust approach for testing whether hybrid origin of asexuality is also a common phenomenon in aphids.

Neuropeptide and neurohormone precursors in the pea aphid, Acyrthosiphon pisum

Abstract: Aphids respond to environmental changes by developing alternative phenotypes with differing reproductive modes. Parthenogenetic reproduction occurs in spring and summer, whereas decreasing day lengths in autumn provoke the production of sexual forms. Changing environmental signals are relayed by brain neuroendocrine signals to the ovarioles. We combined bioinformatic analyses with brain peptidomics and cDNA analyses to establish a catalogue of pea aphid neuropeptides and neurohormones. 42 genes encoding neuropeptides and neurohormones were identified, of which several were supported by expressed sequence tags and/or peptide mass analyses. Interesting features of the pea aphid peptidome are the absence of genes coding for corazonin, vasopressin and sulfakinin and the presence of 10 different genes coding insulin related peptides, one of which appears to be very abundantly expressed.

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Genome Sequence of the Pea Aphid Acyrthosiphon pisum

Abstract: 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.

Facultative Symbionts in Aphids and the Horizontal Transfer of Ecologically Important Traits

Abstract: Aphids engage in symbiotic associations with a diverse assemblage of heritable bacteria. In addition to their obligate nutrient-provisioning symbiont, Buchnera aphidicola, aphids may also carry one or more facultative symbionts. Unlike obligate symbionts, facultative symbionts are not generally required for survival or reproduction and can invade novel hosts, based on both phylogenetic analyses and transfection experiments. Facultative symbionts are mutualistic in the context of various ecological interactions. Experiments on pea aphids (Acyrthosiphon pisum) have demonstrated that facultative symbionts protect against entomopathogenic fungi and parasitoid wasps, ameliorate the detrimental effects of heat, and influence host plant suitability. The protective symbiont, Hamiltonella defensa, has a dynamic genome, exhibiting evidence of recombination, phage-mediated gene uptake, and horizontal gene transfer and containing virulence and toxin-encoding genes. Although transmitted maternally with high fidelity, facultative symbionts occasionally move horizontally within and between species, resulting in the instantaneous acquisition of ecologically important traits, such as parasitoid defense.