In the last decade, much progress has been made towards a basic understanding of RNA silencing mechanisms in plants, like in animals and other eukaryotes. Many events that were already known, such as pathogen-derived resistance, posttranscriptional gene silencing, and microRNA (miRNA)-mediated regulation, were found to share a fundamentally similar mechanism. By taking advantage of such mechanisms, whether deliberately or not, we can suppress some biological activities by targeting a specific gene function. This type of applied approach is known as RNA interference (RNAi). For many years, scientists have been trying to modify inherent activities of plants to improve their yield and quality. Suppression of some biological activities by RNAi would help to achieve such goals.