Characterization of the importance of terminal residues for southern rice black-streaked dwarf virus P9-1 viroplasm formations

Southern rice black-streaked dwarf virus (SRBSDV) P9-1 is involved in viroplasm formations in the SRBSDV-infected plants and insects. During infection, SRBSDV P9-1 is an important protein. However, the function characterization of P9-1 octamers in vitro and in yeast is still obscure. In this study, the secondary and 3D structure of SRBSDV P9-1 was predicted, then SRBSDV P9-1 was expressed and analyzed in vitro, a size exclusion chromatography assay showed that P9-1 had the ability to form octamers in vitro. Mutational analysis of terminal residues showed that the C-terminal arm (residues 324-347) of P9-1 was importance for the formation of octamers. Furthermore, a yeast two-hybrid assay showed that there were strong interactions between the full-length P9-1s, after deleting the C-terminal arm of P9-1, the interactions between the truncated P9-1s were disappeared in yeast. Collectively, the non-structural protein P9-1 played an essential role in self-interact viroplasm formation in vitro and in yeast, and the C-terminal arm region of P9-1 was important for assembling octamers in vitro.