Characterization of homologous and heterologous interactions between viroplasm proteins P6 and P9-1 of the fijivirus southern rice black-streaked dwarf virus.

P6 of southern rice black-streaked dwarf virus (SRBSDV) is a multifunctional protein that is involved in the formation of viroplasms by interacting with P5-1. Here, we used yeast two-hybrid and bimolecular fluorescence complementation assays to show that there were homologous and heterologous interactions between SRBSDV P6 and P9-1 in yeast and plant cells. Mutational analysis showed that the N-terminal region (residues 1-93) of P6 was necessary for the interaction between P6 and P9-1. Self-interactions only occurred between the full-length P6 or P9-1. P9-1 was able to form viroplasm-like inclusion structures alone in the absence of other viral proteins.