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The mechanism of action for engineering viral resistance in plants such as papaya.
What is scientists identify a piece of RNA from the "target" virus, and then build a transgene with a sequence designed to create the viral RNA. The transgene is inserted into the genome of a plant cell, which in turn is grown into a plant. In every cell of that plant and its offspring, the inserted transgene is "transcribed" into viral RNA. Thus, it arms the gene silencing mechanism to be on the lookout for the target virus.