Abstract
BackgroundAcetylation of promoter nucleosomes is tightly correlated and mechanistically linked to gene activity. However, transcription is not necessary for promoter acetylation. It seems, therefore, that external and endogenous stimuli control histone acetylation and by this contribute to gene regulation. Photosynthetic genes in plants are excellent models with which to study the connection between stimuli and chromatin modifications because these genes are strongly expressed and regulated by multiple stimuli that are easily manipulated. We have previously shown that acetylation of specific histone lysine residues on the photosynthetic phosphoenolpyruvate carboxylase (Pepc) promoter in maize is controlled by light and is independent of other stimuli or gene activity. Acetylation of upstream promoter regions responds to a set of other stimuli which include the nutrient availability of the plant. Here, we have extended these studies by analysing histone acetylation during the diurnal and circadian rhythm of the plant.ResultsWe show that histone acetylation of individual lysine residues is removed from the core promoter before the end of the illumination period which is an indication that light is not the only factor influencing core promoter acetylation. Deacetylation is accompanied by a decrease in gene activity. Pharmacological inhibition of histone deacetylation is not sufficient to prevent transcriptional repression, indicating that deacetylation is not controlling diurnal gene regulation. Variation of the Pepc promoter activity during the day is controlled by the circadian oscillator as it is maintained under constant illumination for at least 3 days. During this period, light-induced changes in histone acetylation are completely removed from the core promoter, although the light stimulus is continuously applied. However, acetylation of most sites on upstream promoter elements follows the circadian rhythm.ConclusionOur results suggest a central role of upstream promoter acetylation in the quantitative regulation of gene expression in this model gene. Induced core promoter acetylation is dispensable for the highest gene expression in the diurnal and circadian rhythm.
Highlights
Acetylation of promoter nucleosomes is tightly correlated and mechanistically linked to gene activity
Guo et al suggested that H3K9 acetylation in Arabidopsis is required for the binding of RNA Polymerase II to promoters of light-regulated genes [3] and a similar scenario has been suggested for H3K14 acetylation and transcription on the seed-specific Opaque2 gene in maize [4]
Diurnal promoter activity and histone acetylation on phosphoenolpyruvate carboxylase (Pepc) The maize Pepc gene is highly active in the leaves of illuminated plants
Summary
Acetylation of promoter nucleosomes is tightly correlated and mechanistically linked to gene activity. Transcription is not necessary for promoter acetylation It seems, that external and endogenous stimuli control histone acetylation and by this contribute to gene regulation. We have previously shown that acetylation of specific histone lysine residues on the photosynthetic phosphoenolpyruvate carboxylase (Pepc) promoter in maize is controlled by light and is independent of other stimuli or gene activity. Comprehensive data for individual acetylation sites are not available from plants, many studies of individual genes, or groups of genes, indicate that this correlation is conserved in the green lineage. Guo et al suggested that H3K9 acetylation in Arabidopsis is required for the binding of RNA Polymerase II to promoters of light-regulated genes [3] and a similar scenario has been suggested for H3K14 acetylation and transcription on the seed-specific Opaque gene in maize [4]. The code can store and integrate information about environmental and endogenous stimuli that are important for the regulation of gene activity
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