Figure 4. Schematic representation of PTGS. The viral RNA (vRNA) copied into double-stranded viral RNA (v dsRNA) by the virus-encoded RNA-dependent RNA polymerase (vRdRP). The v dsRNA in turn is processed to small antisense RNA (v asRNA) that mediated PTGS. The v asRNA is also able to anneal to the sense RNA transcript of the transgenes (tr dsRNA) and prime SDE-1 dependent synthesis of double-strande RNA (tr dsRNA). The tr dsRNA is then processed into small antisense RNA (Tr asRNA) that mediates PTGS and is also able to anneal with the tr RNA. The numbers 1-7 refer to different stages in the process.