SNF2 chromatin remodeler-family proteins FRG1 and -2 are required for RNA-directed DNA methylation

Abstract

DNAmethylation in Arabidopsis thaliana is maintained by at least four different enzymes: DNA METHYLTRANSFERASE1 (MET1), CHROMOMETHYLASE3 (CMT3), DOMAINS REARRANGED METHYLTRANSFERASE2 (DRM2), and CHROMOMETHYLASE2 (CMT2). However, DNA methylation is established exclusively by the enzyme DRM2, which acts in the RNA-directed DNA methylation (RdDM) pathway. Some RdDM components belong to gene families and have partially redundant functions, such as the endoribonucleases DICER-LIKE 2, 3, and 4, and INVOLVED IN DE NOVO2 (IDN2) interactors IDN2-LIKE 1 and 2. Traditional mutagenesis screens usually fail to detect genes if they are redundant, as the loss of one gene canbe compensated by a related gene. In an effort to circumvent this issue, we used coexpression data to identify closely related genes that are coregulatedwith genes in the RdDM pathway. Here we report the discovery of two redundant proteins, SNF2-RING-HELICASE-LIKE1 and -2 (FRG1 and -2) that are putative chromatin modifiers belonging to the SNF2 family of helicase-like proteins. Analysis of genome-wide bisulfite sequencing shows that simultaneous mutations of FRG1 and -2 cause defects in methylation at specific RdDM targeted loci. We also show that FRG1 physically associates with Su(var)3-9-related SUVR2, a knownRdDM component, in vivo. Combined, our results identify FRG1 and FRG2 as previously unidentified components of the RdDM machinery.