Abstract
Due to their capability of eliciting a form of posttranscriptional gene silencing (termed virus-induced gene silencing or VIGS), plant viruses are increasingly used as reverse-genetics tools for functional characterization of plant genes. RNA viruses have been shown to trigger silencing in a variety of host plants, including members of Solanacae and Arabidopsis (Arabidopsis thaliana). Several factors affect the silencing response, including host range and viral tropism within the plant. The work presented here demonstrates that a modified tobacco rattle virus (TRV) vector retaining the helper protein 2b, required for transmission by a specific vector nematode, not only invades and replicates extensively in whole plants, including meristems, but also triggers a pervasive systemic VIGS response in the roots of Nicotiana benthamiana, Arabidopsis, and tomato (Lycopersicon esculentum). This sustained VIGS response was exemplified by the silencing of genes involved in root development (IRT1, TTG1 [transparent testa glabra], RHL1 [root hairless1], and beta-tubulin), lateral root-meristem function (RML1 [root meristemless1]), and nematode resistance (Mi). Roots of silenced plants exhibit reduced levels of target mRNA and phenocopy previously described mutant alleles. The TRV-2b vector displays increased infectivity and meristem invasion, both key requirements for efficient VIGS-based functional characterization of genes in root tissues. Our data suggest that the TRV helper protein 2b may have an essential role in the host regulatory mechanisms that control TRV invasion.