Final Report Summary - REVOLUTION (RNA silencing in regulation and evolution)
A second major finding concerned positive feedback mechanisms in RNA silencing at the posttranscriptional level. We established that small RNA can trigger new production of secondary siRNA provided that it is specifically 22nt long. We knew previously that secondary siRNA production triggered cascades of RNA silencing but we did not understand why these cascades are constrained. The requirement for small RNA of a specific length provides a partial explanation because most of the small RNA is either 21nt or 24nt long and produced through pathways that compete with the 22nt RNA pathway. This finding will help understand genetic regulatory cascades and networks in plants. New findings that emerged towards the end of this project will be important in the understanding of regulatory networks. These data that are being written up after the project finished have shown that there is an additional unsuspected initiation stage of RNA-mediated epigenetic change. We knew previously about establishment and maintenance phases but now we understand that there is this earlier initiation process about which there are few details at present. We will investigate the mechanism and its application in follow up work.
The third major line of research in REVOLUTION related to mobile small RNA. Until recently RNA was considered as a molecule that is a coding sequence or regulator operating within a cell. Viruses were known as mobile RNA but cellular RNAs were thought to remain inside a cell. We designed an approach based on grafting different genotypes of plant and thereby confirmed that small silencing RNA can indeed move and that it mediates epigenetic silencing in the recipient cell. The biological implications of this finding remain to be discovered and at present we can only say that the epigenetic sRNAs are likely to be implicated in many of the epigenetic marks in plant genomes. In future work we intend to find out to whether we can harness mobile small RNA to target the introduction of heritable epigenetic effects on plant genotypes. We will be aiming to generate epigenetically modified crop plants.