Biogenesis and Biological Activity of Secondary siRNAs in Plants
Viral dsRNA formation. (a) RNA-virus RNAs are replicated by viral RNA polymerases producing plus strands from a minus strand and vice versa. Occasionally, dsRNA is formed, namely, before the viral strands can be packaged or are protected by ribosomes. (b) Read-through transcription prior to polyadenylation leads to overlapping transcripts in geminiviruses. (c) Cauliflower mosaic virus and other caulimoviruses produce a specific dsRNA covering the leader region. This dsRNA and its siRNA products are thought to act as decoy, the latter by forming nonfunctional RISCs.