Résumé
Nearly all plant viruses use specific vectors to spread from one host to another, the most common vectors being insects, especially aphids. The predominant strategy for virus–vector interaction is the so-called non-circulative transmission, in which the virus is taken up by a vector on an infected plant, attached to unknown receptors somewhere in the feeding apparatus, and subsequently released to inoculate a new host plant. The most precise data on these enigmatic binding sites in insect mouthparts came from a recent pioneering study using Cauliflower mosaic virus (CaMV), a non-circulative virus, to search for receptor molecules in the aphid vectors. A novel in vitro system allowed rapid visualization of the interaction between dissected aphid stylets and the CaMV ligand protein. This provided the first direct evidence for the existence, the precise localization and the chemical nature of a true receptor molecule used by a plant virus in the vector’s mouthparts. The receptor molecules are concentrated exclusively in a tiny area located in the common duct at the extreme distal tip of the aphid maxillary stylets, and are non-glycosylated proteins strongly linked to and deeply embedded into the chitin matrix (Uzest et al., 2007). Using transmission and scanning electron microscopy for further investigating the ultra-structure of this area, we uncovered an intriguing anatomical zone, lining the bed of the common duct in each maxillary stylet, that had thus far been overlooked. This area appears as a swelling of the cuticle surface that perfectly matches the area where the CaMV is specifically binding. It is present at all developmental stages of the aphid vectors, and also found in aphid species that do not transmit CaMV. We are currently investigating the protein contents, the ultrastructure, the biochemical and biological properties of this peculiar structure, in order ultimately to elucidate its physiological function, presumably in the feeding process of aphids or in their relationship with the host plant.