ROS3 an RNA-binding protein required for DNA demethylation in Arabidopsis

摘要

DNA methylation is an important epigenetic mark for transcriptional gene silencing (TGS) in diverse organisms^–. Recent studies suggest that the methylation status of a number of genes is dynamically regulated by methylation and demethylation^–. In Arabidopsis, active DNA demethylation is mediated by the ROS1 (repressor of silencing 1) subfamily of 5-methylcytosine DNA glycosylases through a base excision repair pathway^,–. These demethylases play critical roles in erasing DNA methylation and preventing TGS of target genes^,,. However, it is not known how the demethylases are targeted to specific sequences. We report here the identification of ROS3, an essential regulator of DNA demethylation that contains an RNA recognition motif. Analysis of ros3 mutant and ros1ros3 double mutant suggests that ROS3 acts in the same genetic pathway as ROS1 to prevent DNA hypermethylation and TGS. Gel mobility shift assays and analysis of ROS3 immunoprecipitate from plant extracts showed that ROS3 binds to small RNAs in vitro and in vivo. Immunostaining shows that ROS3 and ROS1 proteins colocalize in discrete foci dispersed throughout the nucleus. These results demonstrate a critical role for ROS3 in preventing DNA hypermethylation and suggest that DNA demethylation by ROS1 may be guided by RNAs bound to ROS3.