Gene silencing in plants, in which an endogenous gene is suppressed by
introduction of a related transgene, has been used for crop improveme
nt. Observations that viruses are potentially both initiators and targ
ets of gene silencing suggested that this phenomenon may be related to
natural defense against viruses. Supporting this idea, it was found t
hat nepovirus infection of nontransgenic plants induces a resistance m
echanism that is similar to transgene-induced gene silencing.