The role of viroids in gene silencing: the model case ofPeach latent mosaic viroid

In plants, RNA silencing plays important roles in antiviral defense, host genome integrity and development. The process can be divided into RNA-mediated transcriptional and posttranscriptional gene silencing. The ability of viroids, which are small circular RNAs that infect higher plants and cause significant economic losses in agriculture, to induce both of these mechanisms has been demonstrated. Consequently, these RNA genomes appear to be suitable for the study of RNA silencing. In presenting useful strategies for detecting viroid-associated posttranscriptional gene silencing, as well as original results suggesting how Peach latent mosaic viroid induces it, this work reviews the current understanding of RNA silencing, a process which constitutes the latest revolution in molecular biology. RNA silencing has gained a lot of attention as a tool for the selective inhibition of gene expression. Clearly, we are only beginning to appreciate the complexity of this mechanism, as well as its biological diversity and potential applications.