Etude des effets de la protéine P1 et du virus de la panachure jaune du riz (Rice yellow mottle virus) sur l'extinction post-transcriptionnelle des gènes : application à la construction de vecteurs viraux chez le riz

Most plant viruses have evolved to conteract the defence mechanism based on RNA silencing. Thus, many viral proteins have been well studied for their features in silencing suppression. Among these proteins, P1 protein from Rice yellow mottle virus, responsible for serious disease in irrigated rice systems in Africa, has been described. This study characterised silencing suppression features of RYMV under natural infection on rice plants. Biolistic delivery assays on rice leaves and Agrobacterium-based leaf infiltration assays on Nicotiana benthamiana, determined that P1 undergoes silencing with variable efficiency when inoculating different P1. Moreover, as RYMV is a highly diverse virus, both at genetic scale or at pathogenicity scale, we attempted to evaluate variability of silencing suppression with RYMV particles. Infected O. Sativa with different RYMV isolates, exhibited contrasted silencing suppression on uidA transgene. We thus revealed that RYMV has a qualitative effect on silencing suppression, which is not correlated to virus phylogeny. Silencing suppression at virus scale was also inversely correlated to pathogenicity of isolates. These results suggested that silencing suppression occuring under RYMV infection, is a complex mechanism. Thus, the involvement of the coat protein, on miRNA accumulation regulation, was demonstrated in transgenic rice lines expressing this protein. Moreover these results will be usefull to improve RYMV-based expression and VIGS vectors, that have been developed in a second study. The purpose of this work is to assess the ability of construction of RYMV-based expression and VIGS vectors and to evaluate gene insertion constraint.