Expression data for the mom1-2 mutant of Arabidopsis

Heterochromatin is an inert region in the genome and composed of mainly remnants of transposons and repetitive elements. In Arabidopsis, the major heterchromatin regions are present at around centromeres (pericentromeric regions) and at a region on the short arm of chromosome 4 (heterochromatin knob). Histones and DNAs in heterochromatin have characteristic features with abundant H3H9me2 and cytosine methylation, respectively. Here, by using a genome tiling array, we showed that a subset of heterochromatin loci are silenced by the action of Morpheus' molecule 1 (MOM1) that is an epigeneic regulator for transcriptional gene silencing independent of global DNA and histone modification. Most of the up-regulated loci in the mom1 mutant carried sequences related to transposable elements but none of them was annotated as functional transposons. No specific subclass of transposons was targeted by MOM1 and loci that were unrelated to transposons but flanked by short tandem repeats were also shown to be under the control of MOM1. The results suggest the presence of an unknown level of regulatory network maintaining the silent state of heterochromain in the genome. Keywords: Epigenetic regulation of endogenous loci by Morpheus' Molecule 1 (MOM1) Three-week-old Arabidopsis plants (Col-0 and mom1-2) grown on soil were subjected to RNA extraction and the total RNA samples were used for the microarray hybridization. Three replicative hybridization experiments for each strand array were carried out using the independent biological RNA samples.