Southern rice black-streaked dwarf virus P8 protein facilitates viral infection by interacting with the C-terminal region of OsARF15

Southem rice black-streaked dwarf virus (SRBSDV), a fijivirus with a double-stranded RNA genome of 10 segments and 13 proteins, severely impairs rice growth and development. The functions of P8, one of the major coat proteins of SRBSDV, are still poorly understood. In this study, the SRBSDV-encoded P8 protein was used as bait in a yeast two-hybrid screen of a rice cDNA library, which identified an interaction between P8 and auxin response factor 15 (OsARF15). The interaction was then confirmed by GST pull-down (in vitro) and co-immunoprecipitation (Co-IP) (in vivo) assays. Truncated protein analysis further revealed that P8 primarily binds to the C-terminal region of OsARF15. Over-expression and knockout of OsARF15 rice plants were constructed and then inoculated by SRBSDV. The results showed that over-expression of OsARF15 promoted SRBSDV infection whereas its knockout enhanced virus resistance. Meanwhile, the effect of OsARF15 on root development was observed and found that knocking out OsARF15 significantly promoted the growth of rice roots at the seeding stage. These results demonstrate that the SRBSDV P8 protein facilitates viral infection by interacting with the C-terminal region of OsARF15. Our findings have further strengthened the role of P8 in the viral infection process.