Résumé
The Cauliflower mosaic virus (CaMV) is the member type of the family Caulimoviridae (genus Caulimovirus) which, together with hepadnaviruses, constitute the para-phylletic group of pararetroviruses having a DNA-based genome replicated via reverse transcription of a pre-genomic RNA. The approximately 8 kpb circular double-stranded DNA genome of CaMV encodes eight major open reading frames. CaMV is transmitted from plant to plant through a seemingly simple interaction with insect vectors. This process involves an aphid receptor and two viral proteins, P2 and P3. P2 binds to both the aphid receptor and P3, itself tightly associated with the virus particle, with the ensemble forming a transmissible viral complex. Additionally, the viral complex is also able to bind microtubules through P2, allowing a rapid spreading of the virus into plant cells and consequently its uptake by the insect. In the present study, we report an integrated structural characterization of P2. We succeeded in production, purification and crystallisation of a P2 mutant corresponding to a deletion of the first coiled-coil helix α1. The structure shows clearly two completely independent domains in which a central core is formed by four coiled-coil α-helix, surrounded by 4 short ß sheets. These data combined with our results obtained by cryo-electron microscopy of P2-decorated microtubules and cryo-electron tomography of P2 para-crystals allow us to gain new insight into molecular mechanism of transmission.