Transcription factor dependent rearrangement of chromatin structure as a regulatory mechanism controlling gene expression at different environmental conditions in Chlamydomonas reinhardtii
Daniela Strenkert, Stefan Schmollinger, Frederik Sommer, Miriam Schulz-Raffelt, and Michael Schroda
Institute for Molecular Plant Physiology, Potsdam-Golm 14476, Germany
Regulation of transcription in eukaryotes is realized by the recruitment of specific transcription factors and chromatin-remodeling enzymes. In this work, we show by Chromatin-Immuno-Precipitation (ChIP) that chromatin remodeling plays an important role during the cellular response of Chlamydomonas to two different environmental conditions, heat shock and copper starvation. Response to each condition is regulated by a specific key regulator that controls a unique set of genes: heat shock by heat shock factor 1 (HSF1) and copper starvation by copper responsive regulator 1 (CRR1). The specific down regulation or knock-out of HSF1 and CRR1 and parallel monitoring of chromatin states and transcriptional activity for inducible downstream genes (HSP70A, HSP22F, CYC6, CPX1) enable us to reveal links between transcription factor dependent gene expression and underlying chromatin structure. Our data correlates with observations made so far in other organisms. The acetylation of histone H3/H4 is most present at the promoter regions of active genes, whereas H3K4 dimethylation seems, like in yeast and animals, to occur at potentially active genes. Promoters of inducible genes investigated in this work show an increase of acetylation of histones H3/H4 and a hence resulting decrease of the histone occupancy after transcriptional induction. These effects are reduced/absent in the corresponding mutant strains indicating the recruitment of chromatin remodeling enzymes by the respective TF. Our results establish Chlamydomonas as a viable model for investigating the relationship between chromatin structure and environmental effects on gene expression.
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