title: Heat shock factor 1 counteracts epigenetic silencing of nuclear transgenes in Chlamydomonas reinhardtii.
abstract: We found previously that the Chlamydomonas HSP70A promoter counteracts transcriptional silencing of downstream promoters in a transgene setting. To elucidate the underlying mechanisms, we analyzed chromatin state and transgene expression in transformants containing HSP70A-RBCS2-ble (AR-ble) constructs harboring deletions/mutations in the A promoter. We identified histone modifications at transgenic R promoters indicative for repressive chromatin, i.e. low levels of histone H3/4 acetylation and H3-lysine 4 trimethylation and high levels of H3-lysine 9 monomethylation. Transgenic A promoters also harbor lower levels of active chromatin marks than the native A promoter, but levels were higher than those at transgenic R promoters. Strikingly, in AR promoter fusions, the chromatin state at the A promoter was transferred to R. This effect required intact HSE4, HSE1/2 and TATA-box in the A promoter and was mediated by heat shock factor (HSF1). However, time-course analyses in strains inducibly depleted of HSF1 revealed that a transcriptionally competent chromatin state alone was not sufficient for activating the R promoter, but required constitutive HSF1 occupancy at transgenic A. We propose that HSF1 constitutively forms a scaffold at the transgenic A promoter, presumably containing mediator and TFIID, from which local chromatin remodeling and polymerase II recruitment to downstream promoters is realized.
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Strenkert
authors.forename: Stefan
authors.initials: S
authors.lastname: Schmollinger
authors.forename: Michael
authors.initials: M
authors.lastname: Schroda
mesh_terms: D000107:Acetylation; D002467:Cell Nucleus / Q000235:genetics; D016825:Chlamydomonas reinhardtii / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D008745:Methylation; D010940:Plant Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics; D016385:TATA Box; D014157:Transcription Factors / Q000378:metabolism*; D019076:Transgenes
chemical_list: D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; D006657:Histones; D010940:Plant Proteins; D014157:Transcription Factors; D012273:Ribulose-Bisphosphate Carboxylase