Fig. 1

a The major genomic elements have distinct chromatin states, each characterized by a signature of chromatin marks: proximal promoters (state 2), TSS (state 1), 5′ end of genes (state 3), long coding sequences (state 7), 3′ end of genes (state 6), polycomb chromatin (state 5), distal regulatory intergenic regions (state 4), AT-rich heterochromatin (state 8), and GC-rich heterochromatin (state 9). The occurrence levels of the main chromatin marks that define each state are summarized as follows: high (black), medium (grey), very low or absent (empty box). b Transitions from euchromatin to heterochromatin states. Left: example of a highly expressed Arabidopsis gene (AT5G30495) that is flanked by repressed transposable elements (TEs) in a pericentromeric region of chromosome 5. Right: example of contiguous TEs (AT1TE21710 and AT1TE21715) flanked by expressed genes in one arm of chromosome 1. Note that, in both cases, the transition from repressed heterochromatin (states 8 and 9) to the active euchromatin (state 1) occurs through a defined path of other chromatin states