Involvement o f M ultiple G ene-Silencing P athways in a P aramutation-lik e P henomenon i n Arabidopsis

SUMMARY Paramutation is an epigenetic phenomenon that has been observed in a number of multicellular organisms. The epigenetically silenced state of paramutated alleles is not only meiotically stable but also ‘‘infectious’’ to active homologous alleles. The molecular mechanism of paramutation remains unclear, but components involved in RNA-directed DNA methylation (RdDM) are required. Here, we report a multi-copy pRD29A-LUC transgene in Arabidopsis thaliana that behaves like a paramutation locus. The silent state of LUC is induced by mutations in the DNA glycosylase gene ROS1. The silent alleles of LUC are not only meiotically stable but also able to transform active LUC alleles into silent ones, in the absence of ros1 mutations. Maintaining silencing at the LUC gene requires action of multiple pathways besides RdDM. Our study identified specific factors that are involved in the paramutation-like phenomenon and established a model system for the study of paramutation in Arabidopsis.