| This thesis describes the characterization of a protein identified via a forward genetic screen for factors necessary for the maintenance of the repressive states associated with maize paramutations. Paramutations are deviations from normal Mendelian inheritance patterns wherein endogenous alleles can be heritably altered in their expression pattern in an epigenetic, or non-DNA sequence based, fashion. I identified a protein necessary for the normal action of paramutations as being part of a RNA-directed DNA methylation pathway that is common to all land plants. This pathway is typically implicated in the regulation of repetitive and parasitic sequences within the plant genome. As such, this thesis elucidates potential connections between the heritable repression associated with paramutations and genome defense pathways. Several models are proposed to explain the mechanism by which these defense pathways may act on endogenous, non-parasitic loci. |
