Virus-mediated reprogramming of gene expression in plants

Plant viruses have made many significant contributions to plant biology over the years: they have provided plant researchers with functional promoters, transient expression systems and, most recently, with critical insights into the phenomenon of posttranscriptional gene silencing. Plant virus expression vectors have the ability to either overexpress genes or suppress gene expression in plants. Whereas the 'rules' for gene expression are generally understood conceptually, the mechanisms for the induction of gene silencing are less well understood. Recent advances in the understanding of both the biological role and the mode of action of posttranscriptional gene silencing will affect both the design and the use of plant viral vectors and transgenic plants for either gene-overexpression or gene-silencing applications.