6 research outputs found

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

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    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.Beatriz Sabater-Muñoz... et al

    L'évolution des virus à ARN : rôles de la sélection et de la dérive génétique

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    International audienceLes virus à ARN, tout comme les rétrovirus et pararétrovirus, ont la capacité d'évoluer très rapidement, grâce à des taux de mutations élevés et des temps de génération très courts. Les erreurs de réplication du génome (mutations et recombinaisons « imparfaites ») sont la source d'une grande variabilité. Cependant, des pressions de sélection sculptent les populations virales dans leur diversité en agissant à tous les niveaux du cycle infectieux des virus : stratégies d'expression du génome, interactions avec l'hôte et le vecteur sont les principales cibles de la sélection. La sélection trie en fonction de la valeur adaptative. Le second paramètre important modulant la diversité des populations virales est la dérive génétique qui intervient lorsque la taille efficace de la population est faible, ce qui semble être fréquent lors de l'initiation de l'infection d'un hôte ou d'un tissu. Contrairement à la sélection, la dérive est un facteur largement aléatoire, indépendant de la valeur adaptative et peut avoir pour conséquence la fixation de mutations délétères. Malgré des taux de mutations exceptionnellement élevés, les virus à ARN semblent également répondre aux principes classiques de la génétique des populations, comme cela a été montré au cours des deux dernières décennies

    Sequence analysis of potato leafroll virus isolates reveals genetic stability, major evolutionary events and differential selection pressure between overlapping reading frame products.

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    In order to investigate the genetic diversity of Potato leafroll virus (PLRV), seven new complete genomic sequences of isolates collected worldwide were compared with the five sequences available in GenBank. Then, a restricted polymorphic region of the genome was chosen to further analyse new sequences. The sequences of PLRV open reading frames (ORFs) 3 and 4 were also compared with those of two other poleroviruses and the non-synonymous to synonymous substitution ratio distribution was analysed in overlapping and non-overlapping regions of the genome using maximum-likelihood models. Results confirmed that PLRV sequences from around the world are very closely related and showed that the region encoding protein P0 allowed the detection of three groups of isolates. When compared to other poleroviruses, PLRV was the most conserved in both ORFs 3 and 4. However, the results suggest that important events, such as deletion, mutation at a stop codon and intraspecific homologous recombination events, have occurred during the evolution of PLRV. Finally, it was shown that the translation products of ORFs 0 and 3 are significantly more conserved than those of the overlapping ORFs 1 and 4, respectively. All together, the results allow the proposal of new hypotheses to explain the apparent genetic stability of PLRV and its evolution.Sébastien Guyader and Danièle Giblot Ducra

    Analysis of a three-dimensional structure of potato leafroll virus coat protein obtained by homology modeling

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    Viruses of the family Luteoviridae are ssRNA plant viruses that have particles that exhibit icosahedral symmetry. To identify the residues that might be exposed on the surface of the Potato leafroll virus (PLRV; genus Polerovirus, family Luteoviridae) capsid, and therefore involved in biological interactions, we performed a structural analysis of the PLRV coat protein (CP) on the basis of comparisons with protein sequences and known crystal structures of CPs of other viruses. The CP of PLRV displays 33% sequence similarity with that of Rice yellow mottle virus (genus Sobemovirus) when the sequences were aligned by using the hidden Markov model method. A structure model for PLRV CP was designed by protein homology modeling, using the crystal structure of RYMV as a template. The resulting model is consistent with immunological and site-directed mutagenesis data previously reported. On the basis of this model it is possible to predict some surface properties of the PLRV CP and also speculate about the structural evolution of small icosahedral viruses.Laurent Terradot, Michel Souchet, Vinh Tran and Danièle Giblot Ducray-Bourdi
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