design: Chromatin immunoprecipitation (ChIP) assays were performed as previously described (Saleh, A., Alvarez-Venegas, R. & Avramova, Z. An efficient chromatin immunoprecipitation (ChIP) protocol for studying histone modifications in Arabidopsis plants. Nature Protocols 3, 1018-1025 (2008).) with minor modifications: Briefly, ground seedlings were cross-linked in Crosslink Buffer containing 0.6% formaldehyde, 5 mM -Mercaptoethanol, and protease inhibitors. Chromatin was sonicated using a Bioruptor Plus (Diagenode) with 24 cycles of 30 s on and 30 s off. Immunoprecipitation was performed using antibodies against H3K4me3 (Abcam, ab8580), H3K9me2 (Abcam, ab1220), H3K27me3 (Abcam, ab6002), or H3 (Abcam, ab1791).