Virus-mediated reprogramming of gene expression in plants

Plant viruses have made many significant contributions to plant biology ove r the years: they have provided plant researchers with functional promoters , transient expression systems and, most recently, with critical insights i nto the phenomenon of posttranscriptional gene silencing. Plant virus expre ssion vectors have the ability to either overexpress genes or suppress gene expression in plants. Whereas the 'rules' for gene expression are generall y understood conceptually, the mechanisms for the induction of gene silenci ng are less well understood. Recent advances in the understanding of both t he biological role and the mode of action of posttranscriptional gene silen cing will affect both the design and the use of plant viral vectors and tra nsgenic plants for either gene-overexpression or gene-silencing application s.