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

Abstract

Active DNA demethylation in vertebrates may also be mediated by a DNA repair pathway. De novo DNA methylation of specific genes in plants can be guided by 24-nt small interfering RNAs. However, it is not known how demethylases are targeted to specific sequences. We report here the identification of ROS3, an essential regulator of DNA demethylation that contains an RRM (RNA recognition motif) domain and binds small RNAs. Mutant analysis suggests that ROS3 acts in the same genetic pathway as ROS1 to prevent DNA hypermethylation and TGS, and immunostaining shows that ROS3 and ROS1 colocalize in discrete foci dispersed throughout the nucleus. These results demonstrate a critical role for ROS3 in preventing DNA hypermethyation and suggest that DNA demethylation by ROS1 may be guided by RNAs bound to ROS3.