Zhihuan Gao 1 , Hai-Liang Liu 1 , 2 , Lucia Daxinger 3 , Olga Pontes 4 , Xinjian He 1 , 5 , Weiqiang Qian 1 , Huixin Lin 1 , Mingtang Xie 1 , Zdravko J. Lorkovic 6 , Shoudong Zhang 1 , 5 , Daisuke Miki 1 , Xianqiang Zhan 1 , 5 , Dominique Pontier 7 , Thierry Lagrange 7 , Hailing Jin 8 , Antonius J. Matzke 3 , Marjori Matzke 3 , Craig S. Pikaard 9 , Jian-Kang Zhu 1 , 5
21 April 2010
DNA methylation is an important epigenetic mark in many eukaryotes 1- 5. In plants, 24-nt small interfering RNAs (siRNAs) bound to the effector protein, Argonaute 4 (AGO4) can direct de novo DNA methylation by the methyltransferase DRM2 2, 4- 6. Here we report a new regulator of RNA-directed DNA methylation (RdDM) in Arabidopsis: RDM1. Loss-of-function mutations in the RDM1 gene impair the accumulation of 24-nt siRNAs, reduce DNA methylation, and release transcriptional gene silencing at RdDM target loci. RDM1 encodes a small protein that appears to bind single-stranded methyl DNA, and associates and co-localizes with RNA polymerase II, AGO4 and DRM2 in the nucleus. Our results suggest that RDM1 is a component of the RdDM effector complex and may play a role in linking siRNA production with pre-existing or de novo cytosine methylation. Our results also suggest that although RDM1 and Pol V may function together at some RdDM target sites in the peri-nucleolar siRNA processing center, Pol II rather than Pol V is associated with the RdDM effector complex at target sites in the nucleoplasm.