Circulating virus load determines the size of bottlenecks in viral populations progressing within a host

For any organism, population size, and fluctuations thereof, are of primary importance in determining the forces driving its evolution. This is particularly true for viruses—rapidly evolving entities that form populations with transient and explosive expansions alternating with phases of migration, resulting in strong population bottlenecks and associated founder effects that increase genetic drift. A typical illustration of this pattern is the progression of viral disease within a eukaryotic host, where such demographic fluctuations are a key factor in the emergence of new variants with altered virulence. Viruses initiate replication in one or only a few infection foci, then move through the vasculature to seed secondary infection sites and so invade distant organs and tissues. Founder effects during this within-host colonization might depend on the concentration of infectious units accumulating and circulating in the vasculature, as this represents the infection dose reaching new organs or “territories”. Surprisingly, whether or not the easily measurable circulating (plasma) virus load directly drives the size of population bottlenecks during host colonization has not been documented in animal viruses, while in plants the virus load within the sap has never been estimated. Here, we address this important question by monitoring both the virus concentration flowing in host plant sap, and the number of viral genomes founding the population in each successive new leaf. Our results clearly indicate that the concentration of circulating viruses directly determines the size of bottlenecks, which hence controls founder effects and effective population size during disease progression within a host

A pluricellular way of life for a multipartite virus

BGPI : équipe 2A pluricellular way of life for a multipartite virus. 16. Rencontres de Virologie Végétale (RVV 2017

Localizing Genome Segments and Protein Products of a Multipartite Virus in Host Plant Cells

International audienceA founding paradigm in virology is that the spatial unit of the viral replication cycle is an individual cell. This concept applied to multipartite viruses-which have a genome composed of two or more nucleic acid segments, each individually encapsulated-implies that all segments constituting a viral genome need to coinfect the same host cell for replication to occur. Would this requirement be verified, it would constitute a major cost for extreme cases of multipartition such as the Faba bean necrotic stunt virus (FBNSV, nanovirus) whose genome is composed of eight complementary segments, each encoding a single gene (Grigoras et al., 2009). To address this question, we followed the distribution of the FBNSV genome segments by fluorescence in situ hybridization combined to immunolocalization of the replication-controlling viral protein within the cells of the host plant: Vicia Faba.A rapid and efficient protocol to localize viral transcripts in plant and insect hosts has been developed earlier (Ghanim et al., 2009). We here improve this method by using random-primed labeled probes and apply it to the detection and quantification of the individual segments composing the FBNSV genome. Moreover, we combine this technique with immunolocalization so that both viral segments and proteins can be visualized within the same samples

Characterization of the Acrostyle, an organ present at the tip of aphid maxillary stylets involved in non-circulative virus transmission

International audienc

Identification of the Cauliflower mosaic virus receptor in its insect vector et characterisation of the acrostyle : antibodies library and peptide array approaches

National audienc

Dynamics of the effective size of Cauliflower mosaic virus population during host colonisation

National audienc

The cauliflower mosaic virus transmission helper protein P2 modifies directly the probing behavior of the aphid vector Myzus persicae to facilitate transmission

International audienceThere is growing evidence that plant viruses manipulate their hosts and vectors in ways that increase transmission. However, to date only few viral components underlying these phenomena have been identified. Here we show that cauliflower mosaic virus (CaMV) protein P2 modifies the feeding behavior of its aphid vector. P2 is necessary for CaMV transmission because it mediates binding of virus particles to the aphid mouthparts. We compared aphid feeding behavior on plants infected with the wild-type CaMV strain Cabb B-JI or with a deletion mutant strain, Cabb B-JIΔP2, which does not produce P2. Only aphids probing Cabb B-JI infected plants doubled the number of test punctures during the first contact with the plant, indicating a role of P2. Membrane feeding assays with purified P2 and virus particles confirmed that these viral products alone are sufficient to cause the changes in aphid probing. The behavior modifications were not observed on plants infected with a CaMV mutant expressing P2Rev5, unable to bind to the mouthparts. These results are in favor of a virus manipulation, where attachment of P2 to a specific region in the aphid stylets-the acrostyleexercises a direct effect on vector behavior at a crucial moment, the first vector contact with the infected plant, which is essential for virus acquisition

Understanding the proteomic composition of the acrostyle through novel methods and the identification of cuticular proteins available for viral binding

BGPI : équipe 2The acrostyle is a distinct anatomical region present along the surface of the common duct at the distal tip of the maxillary stylets, after the fusing of the food and salivary canals. This structure is known to be conserved across multiple aphid species which vector plant viruses and is known to contain the receptor of at least one plant virus, Cauliflower mosaic virus(CaMV), and presumably other viruses (Uzest et al., 2007). This receptor is known to be a non-glycosylated protein embedded within the matrix of chitin fibers of the stylet. Additionally a motif present within many RR-2 family proteins was earlier identified in the acrostyle (Uzest et al., 2010). To better characterize the role of the acrostyle in the transmission of non-persistent viruses two novel tools were developed to examine its proteomic composition: a series of cuticular protein(CuP) specific antibodies from across the conserved RR-2 chitin binding consensus domain, and an array of peptides covering the diversity of Acyrthosiphon pisum RR-2 CuPs. Three regions of the RR-2 domain could be detected at the acrostyle at either the surface, or embedded in the chitin matrix. Hybridizations of viral proteins of non-persistent viruses to the peptide array also revealed peptides that specifically bound these non-persistent viruses. From these peptides two conserved motifs within RR-2 family proteins were identified that may have a role in non-persistent viral transmission. Together these results increase the knowledge of peptides within the RR2 CuPs present at the acrostyle and indicate regions which warrant further research