Localization of Cucumber mosaic virus Turnip mosaic virus particles in aphid stylets

Cucumber mosaic virus (CMV, Bromoviridae family) and Turnip mosaic virus (TuMV, Potyviridae family) are non-persistentviruses transmitted by aphids. They are acquired during brief periods (few seconds to several minutes) when aphids feed on infected plants and are inoculated to healthy plants during subsequent feeding. Virions are thought to interact either directly to receptors on the maxillary stylet cuticle (capsid strategy used by Cucumoviruses, CMV) or via an additional viral protein the helper component HC (helper strategy used by Caulimoviruses and Potyviruses, such as TuMV).To identify the location of retention of both of these viruses within aphid stylets two approaches were conducted: (i)transmission electron microscopy (TEM) observations of cross-sections of stylets and (ii) epifluorescence microscopy on viruliferous aphid stylets or on dissected stylets incubated with fluorescently labelled HC or virions.A critical point to ensure the maximum chance of observing virus-stylet interactions is to determine the best virus strain-aphid species pair for transmission, since we suppose the viruses’ interactions with aphid receptor(s) might be more labile , than for P2 and CaMV binding. The second critical step, for in vitro interaction assays is to define a “perfect interaction buffer” to favor the retention of virions or HC. Some additional challenges still need to be solved since we mainly have results on CMV retention sites made by TEM: in vitro interaction assays on dissected stylets has not allowed identification of CMV particles on the maxillary stylets. However,CMV particles were found in the food canal and upper part of the common canal by TEM.Progress with TuMV has also been made as we recently found a TuMV/aphid pair surpassing our previous transmission rates (up to 70% with 1 aphid per plant) and we are now more confident for future experiments. A first series of in vitro interaction assays made with different buffers do not yet allow to define an optimal pH or a specific composition to reach the "perfect interaction buffer". The current results and goals of these experiments will be discussed