Facets of Histone Acetylation Required for Light-Responsive Gene Expression

Histone acetylation is an important componentofchromatin structurethataffectsgene transcription. Hyperacetylation of histones relaxes chromatin structure and is associated with transcriptional activation, whereas hypoacetylation of histones induces chromatin compaction and gene repression. Benhamed et al. (pages 2893–2903) present new information on the effects ofhistone acetylation of chromatin on light-regulated gene expression. This work firmly establishes the pivotal role of Arabidopsis GCN5 and HD1 in controlling histone acetylation levels over several light-responsive genes and makes an important contribution to our understanding oftheroleplayedbychromatin in regulating gene expression. It was previously found that the histone acetyltransferase TAF1 is required for light regulation of gene expression. In this work, the authors show that histone acetyltransferase GCN5andhistonedeacetylaseHD1arealso involved and play opposing roles that may help tofine-tuneand balancelight regulation of gene expression. Mutations of GCN5 resulted in a long hypocotyl phenotype and reduced light-induced gene expression, whereas mutations in HD1 had the opposite effect. The authors further characterize the extent and type of histone acetylation on target promoters and find that TAF1, GCN5, andHD1havedistinctandspecificeffectson histone acetylation required for light regulation of gene expression.