Facteurs d'origine végétale et animale impliqués dans la transmission des phytovirus par puceron – Virus-vection

1. Scientific background and objectives The viral molecular determinants involved in vector-transmission of plant viruses have been extensively studied over the last decades. However, the counterpart of such studies (plant and vector determinants) has been largely overlooked. It is surprising indeed to realize that very scarce information is available about both host factors participating in virus acquisition by the vector, and vector components mediating virus retention and/or transport within the vector and inoculation into a new host. This lack of information is surely due to important technical bottlenecks. This project aims at filling this wide gap and attempts to identify and characterize host and vector factors involved in transmission of two different plant viruses (a Caulimovirus and a Polerovirus). These two viral models are highly complementary as they have adopted two distinct transmission strategies: non-circulative and circulative transmission, respectively, by the same aphid vector. Moreover, Caulimoviruses are widespread within all host tissues, whereas Poleroviruses are phloem-limited. 2. Description of project, methodology The project has been designed to identify cellular factors interacting with virions by different biological, biochemical and proteomic approaches as well as a genetic approach (cDNA library screening in the yeast double hybrid system using viral proteins as a bait). Once identified, these factors will be characterized. Localization of identified candidates will be performed in the plant and in the vector using electron or fluorescence microscopy. Involvement of the candidates in aphid transmission will be evaluated by performing aphid transmission with or without an excess of the candidate expressed in heterologous system. In the plant, the synthesis of the cellular factors exhibiting virion binding ability will either be inhibited (use of A. thaliana knock-out mutants or RNAi) or increased (by over-expression of the cellular gene). Aphid transmission will further be evaluated using the transgenic plants as viral source. Depending of the chemical nature of aphid receptors, involvement of the candidates in aphid transmission will either be analyzed by overexpression or inhibition in the insect or by using drugs able to inhibit interaction between receptor and viral proteins. 3. Expected results This project should lead to identification of non viral factors involved in aphid transmission. Identification of host and vector factors controlling transmission will identify new cellular pathways of the host-virus-vector interaction and reveal whether different viruses (using the same or different transmission strategies) use similar components (i.e. receptor in vector) during their transmission process. In the plant, characterization of plant proteins involved in aphid transmission should identify cellular pathways used by the virus to control its transmission by aphids. It should be added that involvement of plant factors in aphid transmission is a very innovative aspect of the mechanism which is, in our knowledge, not developed in other laboratories. The expected results might open the way to new virus control programs aiming at specifically interrupting the transmission process at the host and/or vector level.