MOS1 (MODIFIER OF snc1) was identified through a genetic screen for suppressors of snc1, an autoimmune mutant caused by a gain-of-function mutation in a TIR-NB-LRR-type Resistance gene. Loss of MOS1 function completely suppresses snc1-mediated autoimmunity. The MOS1 protein contains a BAT2 domain and regulates the expression of SNC1 in a locus-specific manner, but the mechanism on how MOS1 epigenetically regulates SNC1 gene expression is unclear. Here, we report the gene expression pattern and subcellular localization of MOS1. In addition, we analyze and discuss the roles of DNA and histone methylation in mos1-mediated suppression of SNC1 expression.