Nonstructural protein P7-2 encoded by Rice black-streaked dwarf virus interacts with SKP1, a core subunit of SCF ubiquitin ligase

BACKGROUND: Rice black-streaked dwarf virus (RBSDV), a member of the genus Fijivirus within the family Reoviridae, causes severe damage to cereal crops in South East Asia. The protein P7-2, encoded by the second open reading frame of segment S7, is conserved among most plant-infecting fijiviruses, but its function is still obscure. RESULTS: In this study, P7-2 was used as bait in two-hybrid screens of a cDNA library expressing Zea mays proteins. It was found that there is a strong interaction between P7-2 and Z. mays SKP1 (SKP1(Maize)), a core subunit of the multicomponent SCF (SKP1/Cullin1/F-box/Rbx1) E3 ubiquitin ligase. The interaction was then confirmed in leaf epidermal cells of Nicotiana benthamiana by bimolecular fluorescence complementation assay. Further investigations indicated that P7-2 also interacts with SKP1 proteins from other plants, including Arabidopsis thaliana, N. benthamiana,Oryza sativa and Saccharum sinense. The C-terminal fragment of SKP1(Maize) (residues 97–176) and the middle fragment of P7-2 (residues 79–214) are necessary to sustain the interaction, while the C-terminal putative α-helix domain spanning residues 214–295 of P7-2 greatly facilitates the interaction. Agrobacterium-mediated transient suppression assay showed that P7-2 has no obvious activity to suppress local RNA silencing. CONCLUSIONS: Taken together, our results indicated that RBSDV P7-2 can interact with SKP1 proteins from different plants. This is the first report linking a Fijivirus protein to a component of the ubiquitin proteasome system. P7-2 might be a potential F-box protein encoded by RBSDV and involved in the plant-virus interaction through ubiquitination pathway.