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Fig. 2. Mechanisms for generating dsRNA in plants. dsRNA can be generated through replication of ssRNA viruses (A) or transcription of inverted repeats (B). It can also be generated from endogenous genes or transposons whose transcripts become substrates for RNA-directed RNA polymerase (RdRP); the action of Dicer-like enzymes can then amplify the effect, generating primers for RdRP (C). Alternatively, transcription from promoters on opposite strands could yield complementary RNAs that undergo intramolecular pairing.