Knock-down of OsDCL2 in Rice Negatively Affects Maintenance of the Endogenous dsRNA Virus, Oryza sativa Endornavirus

An endogenous double-stranded RNA (dsRNA), which has recently been recognized as the dsRNA virus Oryza sativa endornavirus (OsEV), is found in many strains of cultivated rice (Oryza sativa). Small RNAs derived from OsEV dsRNA were detected, indicating that the RNA silencing machinery recognizes OsEV dsRNA. The existence of OsEV in knock-down (KD) lines of five genes of RNA-dependent RNA polymerase (OsRDR1OsRDR5) or two genes of Dicer-like protein (OsDCL2 or OsDCL3a) was examined to characterize the relationship between the host RNA silencing system and the propagation of this dsRNA virus. OsEV was not detected in OsRDR4-KD or OsDCL2-KD T-1 lines. We attempted to introduce OsEV into these KD lines by crossing them with OsEV-carrying plants because of the efficient transmission of OsEV to F-1 plants via pollen or ova. All OsRDR4-KD but only some OsDCL2-KD F-1 plants contained OsEV. Some OsDCL2-KD F-1 plants consisted of OsEV-carrying and OsEV-free cells. These results suggest that the maintenance of OsEV is unstable in OsDCL2-KD plants. Furthermore, the amount of OsEV-derived small interfering RNA (vsiRNA) in the OsDCL2-KD plants increased relative to the wild type. This increased level of vsiRNA may cause OsEV instability during cell division.