Identification And Analysis Of Rna Silencing Suppressors From Southern Rice Black-streaked Dwarf Virus (Srbsdv) And Rice Black-Streaked Dwarf Virus (Rbsdv)

Southern rice black-streaked dwarf virus (SRBSDV) and Rice black-streaked dwarf virus (RBSDV) are both members of serogroup2of the genus Fijivirus within the family Reoviridae, are propagatively transmitted to rice, maize, barley, wheat and other plant hosts, causing huge economic losses. RBSDV and SRBSDV are dsRNA viruses, how to overcome host RNA silencing mechanism and complete the replication and infection after virus infected host plants is need depth studies. We identified suppressor activity of protein encoded by RBSDV and SRBSDV to clarify the role of virus-encoded proteins in the process of virus resistance to defense of RNA silencing in host plant.By co-infiltration method to analyze inhibitory activity of SP6protein encoded by SRBSDV6genomic fragment, the results show that SP6protein could suppress local and systemic silencing mediated by sense strand RNA, stop the transduction of silencing signal, and reverse GFP silencing, but couldn’t suppress the silencing caused by dsGFP. Therefore, we think SP6is a RNA silencing suppressor encoded by SRBSDV. A mutant of SP6(the second codon of ORF mutated to a stop codon) couldn’t suppress local silencing, the results show that SP6suppress RNA silencing by protein not mRNA. pGR107-SP6express in non-transgenic N. benthamiana enhance the pathogenicity of PVX. Therefore, SP6protein could be a pathogenic factor.Some viruses present in more than one silencing suppressor, so we analyzed the suppressor activity of SP7-1, SP7-2, SP8, SP9-1, SP9-2and SP10protein encoded by SRBSDV. SP7-1and SP9-1encoded by SRBSDV S7and S9could suppress local silencing mediated by sense strand RNA, but couldn’t suppress the silencing caused by dsGFP. SP9-1could stop the transduction of silencing signal, but couldn’t reverse GFP silencing and enhance the pathogenicity of PVX. For the reason that SP7-1and SP9-1could be RNA silencing suppressors encoded by virus.RBSDV and SRBSDV in virus morphology, composition of the genome and evolutionary relationship is very close. Previous studies showed that RBSDV P6could suppress local and systemic silencing by GFP, is a RNA silencing suppressor, and SRBSDV SP6the same for a RNA silencing suppressor, thence, the function of the proteins encoded by SRBSDV and RBSDV are similar. To further confirm this conclusion, we analyzed the suppressor activity of P5-2, P7-1, P7-2, P9-1and P9-2protein encoded by RBSDV. The results show that RBSDV P7-1, P9-1have the similar function with SRBSDV SP7-1, SP9-1could suppress local silencing by sense strand RNA, couldn’t suppress systemic silencing and the silencing caused by dsGFP.