A chromatin-dependent mechanism regulates gene expression at the core of theArabidopsiscircadian clock

Mar 9, 2013Plant signaling & behavior

A DNA-structure-based process controls key gene activity in the Arabidopsis internal clock

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Abstract

Rhythms in H3K4 trimethylation are delayed compared to H3 acetylation in Arabidopsis clock mechanisms.

H3 acetylation and H3K4 trimethylation are key mechanisms in the positive regulation of the circadian clock.
The delayed accumulation of H3K4me3 suggests distinct roles for H3ac and H3K4me3 in circadian regulation.
Inhibitors that block H3K4me3 accumulation lead to increased binding of clock repressors.
Mis-expression of the histone methyltransferase SET DOMAIN GROUP 2 (SDG2/ATXR3) alters H3K4me3 levels and affects oscillator gene expression.
SDG2/ATXR3 may play a significant role in maintaining proper circadian expression in plants.

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The mechanisms of circadian clock function in Arabidopsis rely on the complex relationships among core clock components. The current model of the Arabidopsis oscillator comprises a myriad of repressors but the mechanisms responsible for activation remain largely unknown. In our recent studies, we have demonstrated that the rhythms in H3 acetylation (H3ac) and H3K4 trimethylation (H3K4me3) are a key mechanism at the positive arm of the oscillator. H3K4me3 rhythmic accumulation is delayed compared to that of H3ac, which opens the possibility for separate roles for each mark. Indeed, the use of inhibitors that block H3K4me3 accumulation was concomitant with increased clock repressor binding, suggesting that H3K4me3 might control the timing from activation to repression. Plants mis-expressing the histone methyltransferase SET DOMAIN GROUP 2 (SDG2/ATXR3) displayed altered H3K4me3 accumulation, oscillator gene expression and clock repressor binding, suggesting that SDG2/ATXR3 is a key component contributing to proper circadian expression.

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A chromatin-dependent mechanism regulates gene expression at the core of theArabidopsiscircadian clock

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