Epigenetic control of repetitive sequences in plant genome

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Genomes of vertebrates contain large proportion of repetitive sequences. The repetitive sequences are potential threat to genome stability and controlled by epigenetic modifications, such as DNA methylation. In this project, we examined epigenetic controls of repetitive sequences using a flowering plant Arabidopsis. Through forward genetic approaches, we identified a jmjC-domain-containing protein IBM1, which controls methylation in genes in negative manner (Saze et al 2008 Science). Genome-wide methylation profiling of the ibm1 mutant revealed that IBM1 protein is necessary for excluding DNA methylation from transcribed genes (Miura et al 2009 EMBO J). We also showed that a retrotransposon sequence is critical for imprinted expression of FWA gene (Fujimoto et al 2008 PLoS Genet). In addition, by combination of genetics and genomics, we identified diverse families of mobile endogenous transposons in the Arabidopsis genome (Tsykahara et al 2009 Nature).