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A regulatory hierarchy controls the dynamic transcriptional response to extreme oxidative stress in archaea.

ABSTRACT: Networks of interacting transcription factors are central to the regulation of cellular responses to abiotic stress. Although the architecture of many such networks has been mapped, their dynamic function remains unclear. Here we address this challenge in archaea, microorganisms possessing transcription factors that resemble those of both eukaryotes and bacteria. Using genome-wide DNA binding location analysis integrated with gene expression and cell physiological data, we demonstrate that a bacterial-type transcription factor (TF), called RosR, and five TFIIB proteins, homologs of eukaryotic TFs, combinatorially regulate over 100 target genes important for the response to extremely high levels of peroxide. These genes include 20 other transcription factors and oxidative damage repair genes. RosR promoter occupancy is surprisingly dynamic, with the pattern of target gene expression during the transition from rapid growth to stress correlating strongly with the pattern of dynamic binding. We conclude that a hierarchical regulatory network orchestrated by TFs of hybrid lineage enables dynamic response and survival under extreme stress in archaea. This raises questions regarding the evolutionary trajectory of gene networks in response to stress.

SUBMITTER: Tonner PD

PROVIDER: S-EPMC4287449 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature

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A regulatory hierarchy controls the dynamic transcriptional response to extreme oxidative stress in archaea.

Tonner Peter D PD Pittman Adrianne M C AM Gulli Jordan G JG Sharma Kriti K Schmid Amy K AK

PLoS genetics 20150108 1

Networks of interacting transcription factors are central to the regulation of cellular responses to abiotic stress. Although the architecture of many such networks has been mapped, their dynamic function remains unclear. Here we address this challenge in archaea, microorganisms possessing transcription factors that resemble those of both eukaryotes and bacteria. Using genome-wide DNA binding location analysis integrated with gene expression and cell physiological data, we demonstrate that a bac ...[more]

PMID: 25569531

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Project description:Previous work identified the winged helix-turn-helix DNA binding transcription factor (TF) RosR (encoded by VNG0258H gene), which dynamically regulates expression of more than 300 genes in response to oxidative stress in Halobacterium salinarum (Sharma 2012). RosR is required for survival of oxidants from multiple sources (e.g. H2O2 and paraquat), as deletion mutants are impaired for ROS outgrowth. Genes directly and indirectly controlled by RosR in response to ROS encode macromolecular repair functions. In the current study, we ask which of these genes are direct targets of RosR regulation. Dynamic chromatin immunoprecipitation combined with microarray (ChIP-chip) analysis validates that genes encoding these functions are direct targets of RosR binding and control. In addition, new RosR direct target genes are identified, including those encoding central cellular functions and a surprisingly high number of other TFs. The majority of the 252 sites throughout the genome are RosR-bound in the absence of stress and cleared of RosR binding in the presence of H2O2. However, binding is dynamic, with promoter-specific differences in the timing of RosR-DNA release and re-binding relative to ROS exposure. Halobacterium salinarum harboring VNG0258H(rosR)::myc was grown to mid-logarithmic phase (OD600 ~ 0.2 - 0.4) and either left untreated or exposed to 25 mM H2O2 for 10, 20, and 60 minutes. Transcription factor-chromatin complexes from each treated time point and untreated cultures were then cross-linked in vivo with 1% formaldehyde for 30 min at room temperature and subjected to immunoprecipitation (IP) by virtue of the myc epitope tag as described previously (Schmid et al. 2011). One M-BM-5g of each IP sample was hybridized against matched, mock-treated controls on a custom 2 x 105,000 feature 60-mer oligonucleotide microarray (Agilent Technologies, AMADID 026819). On this high-resolution array, the entire H. salinarum genome was tiled every 30 bp in triplicate. Randomly selected regions of the genome were spotted in quadruplicate. Dye swaps were conducted to correct for bias in incorporation. Seven biological replicate experiments were conducted for VNG0258::myc in the absence of H2O2 and three in the presence of H2O2. Four biological replicate experiments in an H. salinarum strain harboring the empty vector control plasmid were conducted to detect background peaks resulting from technical aspects of the protocol. This yielded a total of at least 18 replicate intensity data points per 30-bp genomic region per condition. DNA fragments were directly labeled with Cy3 and Cy5 dyes (Kreatech) as described previously (Facciotti et al., 2007). Microarray slide hybridization and washing protocols were conducted according to the manufacturerM-bM-^@M-^Ys instructions (Agilent technologies) with the exception that hybridization was conducted in the presence of 37.5% formamide at 68M-KM-^ZC to ensure proper stringency.

Project description:Haloarchaea in their natural environment are exposed to hypersalinity, intense solar radiation, and desiccation, all of which generate high levels of oxidative stress. Previous work has shown that haloarchaea are an order of magnitude more resistant to oxidative stress than most mesophilic organisms. Despite this resistance, the pathways haloarchaea use to respond to oxidative stress damage are similar to those of nonresistant organisms, suggesting that regulatory processes might be key to their robustness. Recently, small regulatory noncoding RNAs (sRNAs) were discovered in Archaea under a variety of environmental conditions. We report here the transcriptional landscape and functional roles of sRNAs in the regulation of the oxidative stress response of the model haloarchaeon Haloferax volcanii Thousands of sRNAs, both intergenic and antisense, were discovered using strand-specific sRNA sequencing (sRNA-seq), comprising 25 to 30% of the total transcriptome under no-challenge and oxidative stress conditions, respectively. We identified hundreds of differentially expressed sRNAs in response to hydrogen peroxide-induced oxidative stress in H. volcanii The targets of a group of antisense sRNAs decreased in expression when these sRNAs were upregulated, suggesting that sRNAs are potentially playing a negative regulatory role on mRNA targets at the transcript level. Target enrichment of these antisense sRNAs included mRNAs involved in transposon mobility, chemotaxis signaling, peptidase activity, and transcription factors.IMPORTANCE While a substantial body of experimental work has been done to uncover the functions of small regulatory noncoding RNAs (sRNAs) in gene regulation in Bacteria and Eukarya, the functional roles of sRNAs in Archaea are still poorly understood. This study is the first to establish the regulatory effects of sRNAs on mRNAs during the oxidative stress response in the haloarchaeon Haloferax volcanii Our work demonstrates that common principles for the response to a major cellular stress exist across the 3 domains of life while uncovering pathways that might be specific to the Archaea This work also underscores the relevance of sRNAs in adaptation to extreme environmental conditions.

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A regulatory hierarchy controls the dynamic transcriptional response to extreme oxidative stress in archaea.

Publications

A regulatory hierarchy controls the dynamic transcriptional response to extreme oxidative stress in archaea.

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