Methods to exploit plant defence mechanisms or changing plant metabolism by RNA silencing show great potential. Interfering RNA can be used to improve plant composition, while enhancing levels of beneficial nutrients, and to improve plant productivity by suppressing undesirable traits and switching resources to more beneficial quality and yield traits. Gene expression in pathogens and pests can be targeted and plants modified to produce dsRNAs, which trigger silencing and affect essential physiological functions in pest or disease-causing organisms. Many of the modes of activity of the micro- and small interfering RNAs (miRNAs, siRNAs), that mediate the silencing effect are not yet fully understood and knowledge of systemic propagation, turnover, specificity etc. of these molecules is limited. This Action will define and coordinate the most important research tasks for the development of these novel transgenic strategies across many EU and nearby countries with inputs from cooperating researchers in Associated countries in N and S America, Australasia etc..