A conditional silencing suppression system for transient expression.

RNA silencing is a powerful tool deployed by plants against viral infection and abnormal gene expression. Plant viruses have evolved a suite of silencing suppressors for counter-defense, which are also widely used to boost transcript and protein accumulation in transient assays. However, only wild type silencing suppressor proteins have been reported to date. Here we demonstrate that P0 of Potato leafroll virus (PLRV), PLP0, can be split into two proteins that only show silencing suppression activity upon co-expression. We cloned each of these proteins in two different constructs and transiently co-infiltrated them in N. benthamiana leaves. We expressed a fluorescent protein from one of the vectors and observed that cells expressing both halves of PLP0 suppressed gene silencing. Further, we showed that Q system of Neurospora crassa, based on co-expression of a transcription activator and inhibitor, is functional in agroinfiltrated leaves of N. benthamiana. Q system combined with the split PLP0 system showed very tight co-expression of Q system's transcriptional activator and inhibitor. Altogether, our experiments demonstrate a functioning conditional silencing suppressor system and its potential as a powerful tool for transient expression in N. benthamiana leaves, as well as the application of the Q system in plants.