Distinct modes of DNA accessibility in plantchromatin

摘要

The accessibility of DNA to regulatory proteins is a major property of the chromatin environment that favours or hinders transcription. Recent studies in flies reported that H3K9me2-marked heterochromatin is accessible while H3K27me3-marked chromatin forms extensivedomains of low accessibility. Here we show that plants regulate DNA accessibility differently.H3K9me2-marked heterochromatin is the least accessible in the Arabidopsis thaliana genome,and H3K27me3-marked chromatin also has low accessibility. We see that very long geneswithout H3K9me2 or H3K27me3 are often inaccessible and generated significantly loweramounts of antisense transcripts than other genes, suggesting that reduced accessibility isassociated with reduced recognition of alternative promoters. Low accessibility of H3K9me2-marked heterochromatin and long genes depend on cytosine methylation, explaining whychromatin accessibility differs between plants and flies. Together, we conclude that restrictionof DNA accessibility is a local property of chromatin and not necessarily a consequence ofmicroscopically visible compaction.