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)