VAPA, an Innovative “Virus-Acquisition Phenotyping Assay” Opens New Horizons in Research into the Vector-Transmission of Plant Viruses

PLOS ONE, Aug 2011

Host-to-host transmission—a key step in plant virus infection cycles—is ensured predominantly by vectors, especially aphids and related insects. A deeper understanding of the mechanisms of virus acquisition, which is critical to vector-transmission, might help to design future virus control strategies, because any newly discovered molecular or cellular process is a potential target for hampering viral spread within host populations. With this aim in mind, an aphid membrane-feeding assay was developed where aphids transmitted two non-circulative viruses [cauliflower mosaic virus (CaMV) and turnip mosaic virus] from infected protoplasts. In this assay, virus acquisition occurs exclusively from living cells. Most interestingly, we also show that CaMV is less efficiently transmitted by aphids in the presence of oryzalin—a microtubule-depolymerising drug. The example presented here demonstrates that our technically simple “virus-acquisition phenotyping assay” (VAPA) provides a first opportunity to implement correlative studies relating the physiological state of infected plant cells to vector-transmission efficiency.

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VAPA, an Innovative “Virus-Acquisition Phenotyping Assay” Opens New Horizons in Research into the Vector-Transmission of Plant Viruses

an Innovative ''Virus-Acquisition Phenotyping Assay'' Opens New Horizons in Research into the Vector-Transmission of Plant Viruses. PLoS ONE 6(8): e23241. doi:10.1371/journal.pone.0023241 VAPA, an Innovative ''Virus-Acquisition Phenotyping Assay'' Opens New Horizons in Research into the Vector- Transmission of Plant Viruses Alexandre Martinie` re 0 1 Jean-Luc Macia 0 1 Guillaume Bagnolini 0 1 Chiraz Jridi 0 1 Aure lie Bak 0 1 Ste phane Blanc 0 1 Martin Drucker 0 1 Ching-Hong Yang, University of Wisconsin-Milwaukee, United States of America 0 Current address: School of Life Sciences, Oxford Brookes University , Gipsy Lane, Oxford , United Kingdom 1 Equipe CaGeTE, INRA, UMR BGPI, Campus International de Baillarguet , Montpellier , France Host-to-host transmission-a key step in plant virus infection cycles-is ensured predominantly by vectors, especially aphids and related insects. A deeper understanding of the mechanisms of virus acquisition, which is critical to vectortransmission, might help to design future virus control strategies, because any newly discovered molecular or cellular process is a potential target for hampering viral spread within host populations. With this aim in mind, an aphid membranefeeding assay was developed where aphids transmitted two non-circulative viruses [cauliflower mosaic virus (CaMV) and turnip mosaic virus] from infected protoplasts. In this assay, virus acquisition occurs exclusively from living cells. Most interestingly, we also show that CaMV is less efficiently transmitted by aphids in the presence of oryzalin-a microtubuledepolymerising drug. The example presented here demonstrates that our technically simple ''virus-acquisition phenotyping assay'' (VAPA) provides a first opportunity to implement correlative studies relating the physiological state of infected plant cells to vector-transmission efficiency. - Transmission is a critical step in the infection cycle of every virus, because it controls dispersal in space and time, thus directly influencing epidemiology. Understanding this process is, besides being of genuine scientific interest, crucial to the development of alternative disease control strategies. Many viruses, especially plant viruses, are vector-transmitted by insects. Among insect vectors, aphids play a dominant role as they transmit about one-third of all known plant viruses (reviewed in [1]). This is due partly to their non-destructive feeding behaviour. When alighting on a new plant, aphids first insert their stylets (the proboscis-like mouth parts) into epidermal and mesophyll cells in order to test plant palatability. These test punctures last only seconds and usually preserve plant cell integrity. Only when the plant is approved by the aphid do more test punctures guide the stylets to the phloem, where aphids settle for prolonged feeding from the sieve tube sap. When the plant is not a host for the aphid, it soon departs, after very few test punctures, and continues the search for a suitable host (reviewed in [2]). Aphids can acquire viruses efficiently during one of these feeding steps, or even during both steps, depending on the viral species (e.g. [3]). Vector-transmission of plant viruses can be classified into two major categories: circulative and non-circulative transmission. In circulative transmission, the acquired virus circulates from the intestine through the vector body to the salivary glands, and is then inoculated with the saliva into a new host. At least equally important is the non-circulative transmission that is used by about half of all known plant viruses (reviewed in [4]). In this transmission mode, transmissible virus particles are never internalised within the vector body; the association is exclusively external, and viruses attach to the chitin cuticle lining the food and/or salivary canals within the stylets bundle during ingestion of sap or infected cell content. The inoculation into another host plant is believed to occur upon release of the virus particle from the attachment sites, most probably by the action of saliva [5,6]. For the non-circulative cauliflower mosaic virus (CaMV), the attachment sites have been shown to be located exclusively at the extreme tip of the stylets bundle, within the so-called common duct where the food and salivary canals combine. In fact, the attachment site of CaMV is a proteinaceous receptor(s) localised to a specific morphological structure called the acrostyle [7,8]. Because other non-circulative viruses are also retained within the common duct [5,6], it is likely that they also use the acrostyle for transmission, although direct experimental proof is lacking. Non-circulative transmission has been regarded historically as a non-specific event where vectors acquire viruses by chance during feeding and drag them along to a new host in their contaminated stylets. However, in recent decades, evidence is accumulating that non-circulative transmission of plant viruses is a specific pheno (...truncated)


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Alexandre Martinière, Jean-Luc Macia, Guillaume Bagnolini, Chiraz Jridi, Aurélie Bak, Stéphane Blanc, Martin Drucker. VAPA, an Innovative “Virus-Acquisition Phenotyping Assay” Opens New Horizons in Research into the Vector-Transmission of Plant Viruses, PLOS ONE, 2011, Volume 6, Issue 8, DOI: 10.1371/journal.pone.0023241