In plants, fungi and perhaps in animals, a consequence of RNA silencing is epigenetic modification of DNA and chromatin and, consequently, modification of chromosome structure and function. These epigenetic modifications are often associated with changes in gene expression - normally silencing but also with gene activation. We are interested in the mechanism of this epigenetic silencing and its effects on chromosome structure and aspects of growth development and evolution of plants. An intriguing possibility, suggested by our work on RNA-mediated epigenetic silencing, is that heritable epigenetic changes could be mediated by siRNAs that are induced in response to disease, stress or other external stimuli.
One set of projects involves RNA polymerase IV. This protein is similar to the well characterised Polymerases I-III. However, Pol IV is distinct in that it is specifically required for biogenesis of RNA in RNA silencing pathways including those involved in epigenetic processes. We are currently testing the biochemical activity and nature of proteins associated with PolIV and characterising the genetic loci that are affected by PolIV mediated silencing.