Locus-specific dependency of endogenous silent loci on MOM1 and non-CG methylation in Arabidopsis thaliana.

RNA-directed modification of histones is essential for maintenance of heterochromatin in higher eukaryotes. In plants, cytosine methylation, especially in non-CG sequence contexts, is tightly related to inactive chromatin, but the mechanisms regulating the coexistence of cytosine methylation and repressive histone modification remain obscure. We recently revealed that MORPHEUS' MOLECULE1 (MOM1) of Arabidopsis thaliana silences endogenous loci related to transposons and homologous to the 24-nt siRNAs accumulated in wild type plants, and suggested that MOM1 transduces RNA-directed DNA methylation (RdDM) signals to repressive histone modification. In this addendum, we focus on the involvement of MOM1 in multiple transcriptional gene silencing (TGS) pathways.