Evolution of Mutational Robustness in an RNA Virus

Mutational (genetic) robustness is phenotypic constancy in the face of mutational changes to the genome. Robustness is critical to the understanding of evolution because phenotypically expressed genetic variation is the fuel of natural selection. Nonetheless, the evidence for adaptive evolution of mutational robustness in biological populations is controversial. Robustness should be selectively favored when mutation rates are high, a common feature of RNA viruses. However, selection for robustness may be relaxed under virus co-infection because complementation between virus genotypes can buffer mutational effects. We therefore hypothesized that selection for genetic robustness in viruses will be weakened with increasing frequency of co-infection. To test this idea, we used populations of RNA phage φ6 that were experimentally evolved at low and high levels of co-infection and subjected lineages of these viruses to mutation accumulation through population bottlenecking. The data demonstrate that viruses evolved under high co-infection show relatively greater mean magnitude and variance in the fitness changes generated by addition of random mutations, confirming our hypothesis that they experience weakened selection for robustness. Our study further suggests that co-infection of host cells may be advantageous to RNA viruses only in the short term. In addition, we observed higher mutation frequencies in the more robust viruses, indicating that evolution of robustness might foster less-accurate genome replication in RNA viruses

Symptom evolution following the emergence of maize streak virus

For pathogens infecting single host species evolutionary trade-offs have previously been demonstrated between pathogen-induced mortality rates and transmission rates. It remains unclear, however, how such trade-offs impact sub-lethal pathogen-inflicted damage, and whether these trade-offs even occur in broad host-range pathogens. Here, we examine changes over the past 110 years in symptoms induced in maize by the broad host-range pathogen, maize streak virus (MSV). Specifically, we use the quantified symptom intensities of cloned MSV isolates in differentially resistant maize genotypes to phylogenetically infer ancestral symptom intensities and check for phylogenetic signal associated with these symptom intensities. We show that whereas symptoms reflecting harm to the host have remained constant or decreased, there has been an increase in how extensively MSV colonizes the cells upon which transmission vectors feed

Interet de la spectroscopie RMN pour l'etude in vivo du metabolisme cerebral dans le cas de pathologies globales et localisees

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 20331 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

New experimental and theoretical approaches towards the understanding of the emergence of viral infections

Peer reviewe

Four Amino Acids of an Insect Densovirus Capsid Determine Midgut Tropism and Virulence

International audienceDensoviruses are insect parvoviruses that are orally infectious for Lepidoptera. To assess the mechanisms underlying their specificity and their virulence, we investigated the role of eight candidate residues in the densovirus capsid. We showed that the substitutions of four amino acids were associated with decreased virulence due to a decreased ability to cross the host midgut epithelium, without an effect on viral replication in other tissues

“French Phage Network”-Second Meeting Report

International audienceThe study of bacteriophages (viruses of bacteria) includes a variety of approaches, such as structural biology, genetics, ecology, and evolution, with increasingly important implications for therapeutic and industrial uses. Researchers working with phages in France have recently established a network to facilitate the exchange on complementary approaches, but also to engage new collaborations. Here, we provide a summary of the topics presented during the second meeting of the French Phage Network that took place in Marseille in November 2016

Increase in taxonomic assignment efficiency of viral reads in metagenomic studies

BGPI Cirad : équipe 7Metagenomics studies have revolutionized the field of biology by revealing the presence of many previously unisolated and uncultured micro-organisms. However, one of the main problems encountered in metagenomic studies is the high percentage of sequences that cannot be assigned taxonomically using commonly used similarity-based approaches (e.g. BLAST or HMM). These unassigned sequences are allegorically called "dark matter" in the metagenomic literature and are often referred to as being derived from new or unknown organisms. Here, based on published and original metagenomic datasets coming from virus-like particle enriched samples, we present and quantify the improvement of viral taxonomic assignment that is achievable with a new similarity-based approach. Indeed, prior to any use of similarity based taxonomic assignment methods, we propose assembling contigs from short reads as is currently routinely done in metagenomic studies, but then to further map unassembled reads to the assembled contigs. This additional mapping step increases significantly the proportions of taxonomically assignable sequence reads from a variety plant, insect and environmental (estuary, lakes, soil, feces) - of virome studies

Differences in Virus Robustness Are Not Confounded by Increased Mutation Frequencies in Viruses Evolved under High Co-Infection

<p>Mean mutation frequency (± 95% confidence interval) was assayed for wild-type ϕ6 (ANC), and for one pre-bottleneck clone isolated from each population evolved under low co-infection (L1–L3) and high co-infection (H1–H3). Assays on <i>P. tomato</i> (circles) and <i>P. atrofaciens</i> (squares) were replicated 5-fold. Assays for <i>P. atrofaciens</i> mutants challenged with growth on <i>P. tomato</i> (diamonds) were replicated 6-fold, except for H3 (<i>n</i> = 2).</p