| description |
Post-translational chromatin modifications are, amongst others, an important regulatory mechanism in light signalling and clock function. While development or adaptation to environmental conditions often involves switches between gene activity or repression, the regulation of diurnal transcript level changes rather requires the fine-tuning of the expression of generally active genes depending on the prevailing environmental conditions. To identify diurnal chromatin modifications that accompany diurnal changes in transcript expression we sequenced chromatin immunoprecipitations (ChIPs) with antibodies against the histone H3 modifications K4me3, K9me2, K9ac, S10p, K27ac and S28p in fully expanded leaves of Arabidopsis thaliana in two different experimental conditions. We found a differential K9ac, K27ac and S28p chromatin modification pattern between the end of the day and the end of the night, which correlates with changes in diurnal transcript levels. Genes carrying this modification pattern contain over-represented promoter elements and the encoded proteins are significantly enriched for transcription factors and over-represented in starch catabolic process and circadian rhythm. In the two different experiments we identified additional activating chromatin modifications, namely S10p in the optimal water experiment and K4me3 in the water deficit experiment with plants grown in 60% soil water content. The data suggest a mechanism for diurnal transcript level regulation in which transcription factors guide chromatin modification complexes and in which the reduced binding of repressive transcription factors allows the placement of activating K9ac, K27ac and S28p chromatin modifications. The presence of the activating chromatin modification pattern only at times when the expression of the corresponding genes is required can explain why some genes are differentially inducible during the diurnal cycle. |