Project description:The transcriptional regulatory structure of plant genomes remains poorly defined relative to that of animals. It has been unclear how many cis-regulatory elements generally exist in plant genomes, where these elements lie in relation to their target promoters, and how these features are conserved across species. We employed the Assay for Transposase-Accessible Chromatin with sequencing (ATAC-seq) in four different plant species (Arabidopsis thaliana, Medicago truncatula, Solanum lycopersicum, and Oryza sativa) to delineate open chromatin regions and transcription factor (TF) binding sites across each genome. Despite a ~10-fold variation in intergenic space among species, the majority of open chromatin regions consistently lie within 3 kb upstream of a transcription start site (TSS) in all four species. Nearly 70% of genes in Arabidopsis, Medicago, and Rice have a single putative regulatory region upstream of the TSS, while a similar percentage of tomato genes have 2-5 such elements. Despite variation in the location and number of regulatory elements within orthologous gene sets, transcriptional regulatory networks appear to be largely conserved across species. Profiling of open chromatin in the Arabidopsis root hair and non-hair epidermal cell types indicated that while the open chromatin landscapes of these two cell types were largely indistinguishable on a global scale, thousands of relatively subtle, quantitative cell-specific differences could be found. Analysis of TF binding sites in these differentially accessible regions led to the discovery of a MYB-driven transcriptional regulatory module unique to the hair cell type, which appears to control both hair cell fate regulators and abiotic stress responses. Our cross-species and cross-cell type analyses revealed common transcriptional regulatory principles among species and shed light on the mechanisms that produce cell type-specific transcriptomes during development.
Project description:Genomic integrity requires faithful chromosome duplication. Origins of replication are the genomic sites where DNA replication initiates in every cell cycle. There are multiple origins scattered throughout the eukaryotic genome whose genome-wide identification has been a hard challenge, especially in multicellular organisms. Thus, very little is known on the distinctive features of origins in terms of DNA sequence and chromatin context at a genomic scale. Here we have profiled origins in Arabidopsis thaliana by high-throughput sequencing of purified nascent DNA strands. We have identified 1543 replication origins, which were uniformly distributed across the Arabidopsis genome and enriched in binding signals of two replication initiation proteins, CDC6 and ORC1. We have also analyzed novel epigenome maps of various histone modifications and found links between origins and epigenetic signatures, which differ from or have not been reported for other eukaryotic systems. Arabidopsis origins tend to be embedded in G+C-rich regions within the 5M-bM-^@M-^Y half of genes, enriched in histone H2A.Z, H3K4me2/3 and acetylated H4, and depleted of H3K4me1 and H3K9me2. Our data establish the basis for the understanding of the epigenetic specification of origins of replication in Arabidopsis and have implications for the mechanisms of origin specification in other eukaryotes. This SuperSeries is composed of the following subset Series: GSE21781: Mapping origins of replication in Arabidopsis thaliana: Examination of BrdU labelled DNA and unlabelled DNA in one cell type GSE21827: Mapping origins of replication in Arabidopsis thaliana: H3K4ac ChIP vs. unmodified H3 ChIP Refer to individual Series
Project description:Gene-expression divergence between species shapes morphological evolution, but the molecular basis is largely unknown. Here we show cis- and trans-regulatory elements and chromatin modifications on gene-expression diversity in genetically tractable Arabidopsis allotetraploids. In Arabidopsis thaliana and Arabidopsis arenosa, both cis and trans with predominant cis-regulatory effects mediate gene-expression divergence. The majority of genes with both cis- and trans-effects are subjected to compensating interactions and stabilizing selection. Interestingly, chromatin modifications correlate with cis - and trans -regulation. In F1 allotetraploids, Arabidopsis arenosa trans factors predominately affect allelic expression divergence. Arabidopsis arenosa trans factors tend to upregulate Arabidopsis thaliana alleles, whereas Arabidopsis thaliana trans factors up- or down-regulate Arabidopsis arenosa alleles. In resynthesized and natural allotetraploids, trans effects drive expression of both homoeologous loci into the same direction. We provide evidence for natural selection and chromatin regulation in shaping gene-expression diversity during plant evolution and speciation. Examination of gene expression in 5 tetraploid Arabidopsis using mRNA-seq
Project description:Distal cell-type-specific regulatory elements may be located at very large distances from the genes that they control and are often hidden within intergenic regions or in introns of other genes. The development of methods that enable mapping of regions of open chromatin genome wide has greatly advanced the identification and characterisation of these elements. Here we use DNase I hypersensitivity mapping followed by deep sequencing (DNase-seq) to generate a map of open chromatin in primary human tracheal epithelial (HTE) cells and use bioinformatic approaches to characterise the distribution of these sites within the genome and with respect to gene promoters, intronic and intergenic regions. Genes with THE-selective open chromatin at their promoters were associated with multiple pathways of epithelial function and differentiation. The data predict novel cell-type-specific regulatory elements for genes involved in HTE cell function, such as structural proteins and ion channels, and the transcription factors that may interact with them to control gene expression. Moreover, the map of open chromatin can identify the location of potentially critical regulatory elements in genome-wide association studies (GWAS) in which the strongest association is with single nucleotide polymorphisms in non-coding regions of the genome. We demonstrate its relevance to a recent GWAS that identifies modifiers of cystic fibrosis lung disease severity. Since HTE cells have many functional similarities with bronchial epithelial cells and other differentiated cells in the respiratory epithelium, these data are of direct relevance to elucidating the molecular basis of normal lung function and lung disease. To identify cis-regulatory elements for genes expressed in human tracheal epithelial cells we generated genome-wide maps of open chromatin by DNase-seq. HTE cells were isolated from these trachea and grown as described previously (Davis P.B. et al.1990).
Project description:We develop a technique, named MNase hypersensitivity sequencing (MH-seq), to identify genomic regions associated with open chromatin in Arabidopsis thaliana. Genomic regions enriched with MH-seq reads are referred as MNase hypersensitive sites (MHSs). MHSs overlap with the majority (~90%) of the open chromatin identified previously by DNase-seq and ATAC-seq. Surprisingly, 22% MHSs are not covered by DNase-seq or ATAC-seq reads, which are referred to “specific MHSs” (sMHSs). sMHSs tend to be located away from promoters and a substantial portion of sMHSs are derived from transposable elements. Most interestingly, genomic regions containing sMHSs are enriched with epigenetic marks, including H3K27me3 and DNA methylation. In addition, sMHSs show a number of distinct characteristics including association with transcriptional repressors. Thus, sMHSs span distinct classes of open chromatin that may not be accessible to DNase I or Tn5. We hypothesize that the small size of the MNase enzyme relative to DNase I or Tn5 allows its access to relatively more condensed chromatin domains.
Project description:We mapped DNaseI hypersensitive sites (DHSs) and applied genomic footprinting to define in vivo transcription factor (TF) occupancy at nucleotide resolution across the A. thaliana genome in whole seedlings during heat- and light-response states. We find that trait-associated variation localizes within DHSs, and that extensive TF occupancy within protein-coding exons has shaped A. thaliana codon usage. Analysis of >700,000 TF footprints disclosed an extensive cis-regulatory lexicon, and enabled construction of large-scale TF cross-regulatory networks. Although the cis- and trans-regulatory repertoire is markedly distinct from mammals, the architecture of A. thaliana TF networks is strikingly similar to those of human. Analysis of the DHS landscape and TF network dynamics during heat shock and photomorphogenesis revealed thousands of conditionally-sensitive elements and enabled mapping of key regulatory circuits. Our results provide an extensive resource for understanding and enabling diverse aspects of A. thaliana biology. Chromatin accessibility profiling (Dnase I-seq) and RNA-seq of 7-day-old dark-grown seedlings exposed to 0hr light, 30min light, 3hr light or 24hr LD conditions. Chromatin accessibility profiling (Dnase I-seq) and RNA-seq of 7-day-old LD-grown seedlings treated with a brief sever heat shock or kept under control conditions. Replicates are included when available; controls and read-normalized samples (samples that were subsampled to the same read-depth) are also included here.
Project description:Gene-expression divergence between species shapes morphological evolution, but the molecular basis is largely unknown. Here we show cis- and trans-regulatory elements and chromatin modifications on gene-expression diversity in genetically tractable Arabidopsis allotetraploids. In Arabidopsis thaliana and Arabidopsis arenosa, both cis and trans with predominant cis-regulatory effects mediate gene-expression divergence. The majority of genes with both cis- and trans-effects are subjected to compensating interactions and stabilizing selection. Interestingly, chromatin modifications correlate with cis - and trans -regulation. In F1 allotetraploids, Arabidopsis arenosa trans factors predominately affect allelic expression divergence. Arabidopsis arenosa trans factors tend to upregulate Arabidopsis thaliana alleles, whereas Arabidopsis thaliana trans factors up- or down-regulate Arabidopsis arenosa alleles. In resynthesized and natural allotetraploids, trans effects drive expression of both homoeologous loci into the same direction. We provide evidence for natural selection and chromatin regulation in shaping gene-expression diversity during plant evolution and speciation.
Project description:We mapped DNaseI hypersensitive sites (DHSs) and applied genomic footprinting to define in vivo transcription factor (TF) occupancy at nucleotide resolution across the A. thaliana genome in whole seedlings during heat- and light-response states. We find that trait-associated variation localizes within DHSs, and that extensive TF occupancy within protein-coding exons has shaped A. thaliana codon usage. Analysis of >700,000 TF footprints disclosed an extensive cis-regulatory lexicon, and enabled construction of large-scale TF cross-regulatory networks. Although the cis- and trans-regulatory repertoire is markedly distinct from mammals, the architecture of A. thaliana TF networks is strikingly similar to those of human. Analysis of the DHS landscape and TF network dynamics during heat shock and photomorphogenesis revealed thousands of conditionally-sensitive elements and enabled mapping of key regulatory circuits. Our results provide an extensive resource for understanding and enabling diverse aspects of A. thaliana biology.