Genetic diversity and silencing suppression effects of Rice yellow mottle virus and the P1 protein.
BACKGROUND
PTGS (post-transcriptional gene silencing) is used to counter pathogenic invasions, particularly viruses. In return, many plant viruses produce proteins which suppress silencing directed against their RNA. The diversity of silencing suppression at the species level in natural hosts is unknown.


RESULTS
We investigated the functional diversity of silencing suppression among isolates of the African RYMV (Rice yellow mottle virus) in rice. The RYMV-P1 protein is responsible for cell-to-cell movement and is a silencing suppressor. Transgenic gus-silencing rice lines were used to investigate intra-specific and serogroup silencing suppression diversity at two different levels: that of the virion and the P1 silencing suppressor protein. Our data provide evidence that silencing suppression is a universal phenomenon for RYMV species. However, we found considerable diversity in their ability to suppress silencing which was not linked to RYMV phylogeny, or pathogenicity. At the level of the silencing suppressor P1 alone, we found similar results to those previously found at the virion level. In addition, we showed that cell-to-cell movement of P1 was crucial for the efficiency of silencing suppression. Mutagenesis of P1 demonstrated a strong link between some amino acids and silencing suppression features with, one on the hand, the conserved amino acids C95 and C64 involved in cell-to-cell movement and the strength of suppression, respectively, and on the other hand, the non conserved F88 was involved in the strength of silencing suppression.


CONCLUSIONS
We demonstrated that intra-species diversity of silencing suppression is highly variable and by mutagenesis of P1 we established the first link between silencing suppression and genetic diversity. These results are potentially important for understanding virus-host interactions.
Siré
Christelle
C
Institut de Recherche pour le Développement (IRD), UMR LGDP, 34394 Montpellier Cedex 5, France. sire.christelle@gmail.com
Bangratz-Reyser
Martine
M
Fargette
Denis
D
Brugidou
Christophe
C
D000595:Amino Acid Sequence; D014644:Genetic Variation; D016296:Mutagenesis; D012275:Oryza / Q000821:virology*; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000821:virology*; D018515:Plant Leaves / Q000235:genetics / Q000821:virology; D010942:Plant Viruses / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D034622:RNA Interference; D012328:RNA Viruses / Q000235:genetics* / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
C112015:P1 protein, Rice yellow mottle virus; D018749:RNA, Plant; D014764:Viral Proteins