Cauliflower mosaic virus (CaMV) is transmitted from plant to plant through an interaction with aphid vectors, according to a non-circulant transmission (1). Until recently, it was admitted that CaMV transmission was not specific. However, our colleagues have recently identified a proteic receptor at the extreme tip of the aphid maxillary stylets involved in interaction with the viral protein P2, the transmission factor of  CaMV, suggesting a specific and complex interaction process (2).

As a consequence, it is now believed that  CaMV transmission involves an aphid receptor and two viral proteins, P2 and P3. P2 binds both to the aphid receptor and to P3, which is tightly associated with the CaMV viral particle, forming the transmissible viral complex (Figure 1). We have previously resolved the P3 structure by X-ray crystallography (3) and proposed a model  for the CaMV:P3 complex based on single particle cryo-electron microscopy (cryo-EM) studies (4). We are now trying to characterize P2, the viral helper-component, which acts as a bridge between the aphid receptor and the viral complex CaMV:P3, thus playing a major role in plant-vector transmission. Structure predictions indicate that P2 is composed by a N-terminal globular domain, followed by two coiled-coil domains. Due to the presence of these coiled-coil domains which seem to confer the protein a strong tendency to aggregate, it is extremely difficult to work and manipulate the native P2 protein. Hence, we have adopted a hybrid strategy combining  X-ray crystallography and cryo-EM studies to investigate the structural organization of P2. In this context, we are trying to crystallize various domains of the P2 protein over-expressed in bacteria. Additionally, we want to obtain the tertiary structure of P2 by using electron microscopy. Indeed, as His-tagged P2 protein can form paracrystals when expressed in sf9 cells (Figure 2), we use  cryo-electron tomography  and sub-tomogram averaging methods to get first structural data on P2 and interactions between coiled-coil domains. Moreover, a P2 mutant (157m) was shown to decorate microtubules in sf9 cells (Figure 3). We defined conditions of purification and used these decorated microtubules to engage a single particle analysis in cryo-EM and image processing.

This poster presents the first structural results in the organization of the P2 protein and its multiple interactions.

(1)    Martinière et al., Plant Signaling & Behavior, 4:6, 548-550, 2009

(2)    Uzest et al., PNAS, vol. 104 no. 46, 17959-17964, 2007

(3)    Hoh et al., Journal of Virology, vol. 84 no. 9, 4706-4713, 2010

(4)    Plisson et al., J. Mol. Biol, 346:267-277, 2005

Figures:

CaMV transmission to aphids

P2 paracrystals in Sf9 cells

P2 mutant (157m) decorating sf9 cell microtubules

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EMC Abstracts - https://emc-proceedings.com/abstract/structural-characterization-of-the-protein-p2-the-aphid-transmission-factor-of-the-cauliflower-mosaic-virus/