Viral suppressors of RNA silencing.

The suppression of RNA silencing by plant viruses represents a viral adaptation to a novel host antiviral defense. Three types of viral suppressors have been identified through the use of a variety of silencing suppression assays. The first two types of suppressor are capable of a complete or partial reversal of pre-existing RNA silencing; the third type does not reverse RNA silencing but can instead prevent its systemic signaling.