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On the mechanisms of circulative non-propagative transmission of nanoviruses

Stephane Blanc: INRA

<div>Among diverse virus-insect vector interactions, the circulative non-propagative transmission has solely been reported for plant viruses. In this mode of transmission, the virus cycles within its insect vector, across cellular barriers of the gut and salivary glands, without replicating. The absence of replication is supported by the view that virus particles may undergo transcytosis at these barriers, traversing cells sequestered into membranous vesicles, thus not in direct contact with the cyctoplasm or nucleoplasm. This has been experimentally shown for the family <em>Luteoviridae,</em> but the mechanisms of cell crossing for the families <em>Gemini-</em> and <em>Nanoviridae</em> remain elusive. In these three families, some observations challenge the total absence of viral replication in the insect vector, denoting in the least that this mode of transmission remains poorly understood.</p> <p>We have initiated the study of the molecular and cellular interactions between aphid vectors and the nanovirus species <em>Faba bean necrotic stunt virus</em> (FBNSV). We have defined the within-vector route of this multipartite virus, where distinct viral genome segments all travel together and specifically accumulate into anterior midgut cells and into one cell type only of the principal salivary glands. Both other and our groups have shown the requirement of a “helper” factor for aphid-transmission of FBNSV. This helper factor is being identified as the product of the genome segment N, the protein NSP. At this point, we have evidence that the NSP protein controls the entry and/or accumulation of FBNSV into the aphid gut cells and further study of its mode of action is in progress.</div>

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