ChIP-on-chip analysis of H3K27me3 levels in leaves and calli

In plants, multiple detached tissues are capable of forming a pluripotent cell mass, termed callus, when cultured with appropriate plant hormones. Recent studies demonstrated that callus resembles the tip of a root meristem, even if it is derived from aerial organs. However, the underlying mechanism that guides differentiated organs to form callus is unknown. Here we show that genome-wide reprogramming of histone H3 lysine 27 trimethylation (H3K27me3) is critical in callus formation. During culture of leaf explants, the H3K27me3 level was decreased first at certain auxin-pathway genes, and then increased at the leaf- but decreased at the root-preferentially expressed genes. In addition, only the root but not the leaf explants of the Polycomb group (PcG) mutants can normally form callus. Our data indicate that PcG and H3K27me3 demethylation pathways act separately in reprogramming of H2K27me3 distributions, and also suggest that this is a general mechanism leading to cell fate transition. We analyzed the genome-wide profiles by the ChIP-on-chip assay to determine genes with altered H3K27me3 modifications between the leaf and the callus