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Hu G, Grover CE, Vera DL, Lung PY, Girimurugan SB, Miller ER, Conover JL, Ou S, Xiong X, Zhu D, Li D, Gallagher JP, Udall JA, Sui X, Zhang J, Bass HW, Wendel JF. Evolutionary Dynamics of Chromatin Structure and Duplicate Gene Expression in Diploid and Allopolyploid Cotton. Mol Biol Evol 2024; 41:msae095. [PMID: 38758089 PMCID: PMC11140268 DOI: 10.1093/molbev/msae095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 04/10/2024] [Accepted: 05/10/2024] [Indexed: 05/18/2024] Open
Abstract
Polyploidy is a prominent mechanism of plant speciation and adaptation, yet the mechanistic understandings of duplicated gene regulation remain elusive. Chromatin structure dynamics are suggested to govern gene regulatory control. Here, we characterized genome-wide nucleosome organization and chromatin accessibility in allotetraploid cotton, Gossypium hirsutum (AADD, 2n = 4X = 52), relative to its two diploid parents (AA or DD genome) and their synthetic diploid hybrid (AD), using DNS-seq. The larger A-genome exhibited wider average nucleosome spacing in diploids, and this intergenomic difference diminished in the allopolyploid but not hybrid. Allopolyploidization also exhibited increased accessibility at promoters genome-wide and synchronized cis-regulatory motifs between subgenomes. A prominent cis-acting control was inferred for chromatin dynamics and demonstrated by transposable element removal from promoters. Linking accessibility to gene expression patterns, we found distinct regulatory effects for hybridization and later allopolyploid stages, including nuanced establishment of homoeolog expression bias and expression level dominance. Histone gene expression and nucleosome organization are coordinated through chromatin accessibility. Our study demonstrates the capability to track high-resolution chromatin structure dynamics and reveals their role in the evolution of cis-regulatory landscapes and duplicate gene expression in polyploids, illuminating regulatory ties to subgenomic asymmetry and dominance.
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Affiliation(s)
- Guanjing Hu
- State Key Laboratory of Cotton Bio-breeding and Integrated, Chinese Academy of Agricultural Sciences, Institute of Cotton Research, Anyang 455000, China
- Shenzhen Branch, Guangdong Laboratory of Lingnan Modern Agriculture, Key Laboratory of Synthetic Biology, Ministry of Agriculture and Rural Affairs, Chinese Academy of Agricultural Sciences, Agricultural Genomics Institute at Shenzhen, Shenzhen 518120, China
| | - Corrinne E Grover
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA 50011, USA
| | - Daniel L Vera
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Pei-Yau Lung
- Department of Statistics, Florida State University, Tallahassee, FL 32306, USA
| | | | - Emma R Miller
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA 50011, USA
| | - Justin L Conover
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA 50011, USA
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA
| | - Shujun Ou
- Department of Molecular Genetics, Ohio State University, Columbus, OH 43210, USA
| | - Xianpeng Xiong
- Shenzhen Branch, Guangdong Laboratory of Lingnan Modern Agriculture, Key Laboratory of Synthetic Biology, Ministry of Agriculture and Rural Affairs, Chinese Academy of Agricultural Sciences, Agricultural Genomics Institute at Shenzhen, Shenzhen 518120, China
| | - De Zhu
- Shenzhen Branch, Guangdong Laboratory of Lingnan Modern Agriculture, Key Laboratory of Synthetic Biology, Ministry of Agriculture and Rural Affairs, Chinese Academy of Agricultural Sciences, Agricultural Genomics Institute at Shenzhen, Shenzhen 518120, China
| | - Dongming Li
- Shenzhen Branch, Guangdong Laboratory of Lingnan Modern Agriculture, Key Laboratory of Synthetic Biology, Ministry of Agriculture and Rural Affairs, Chinese Academy of Agricultural Sciences, Agricultural Genomics Institute at Shenzhen, Shenzhen 518120, China
- Zhengzhou Research Base, State Key Laboratory of Cotton Biology, School of Agricultural Sciences, Zhengzhou University, Zhengzhou 450000, China
| | - Joseph P Gallagher
- Forage Seed and Cereal Research Unit, USDA/Agricultural Research Service, Corvallis, OR 97331, USA
| | - Joshua A Udall
- Crop Germplasm Research Unit, USDA/Agricultural Research Service, College Station, TX 77845, USA
| | - Xin Sui
- Department of Statistics, Florida State University, Tallahassee, FL 32306, USA
| | - Jinfeng Zhang
- Department of Statistics, Florida State University, Tallahassee, FL 32306, USA
| | - Hank W Bass
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Jonathan F Wendel
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA 50011, USA
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Ramakrishnan A, Wangensteen G, Kim S, Nestler EJ, Shen L. DeepRegFinder: deep learning-based regulatory elements finder. BIOINFORMATICS ADVANCES 2024; 4:vbae007. [PMID: 38343388 PMCID: PMC10858349 DOI: 10.1093/bioadv/vbae007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 12/06/2023] [Accepted: 01/12/2024] [Indexed: 06/15/2024]
Abstract
Summary Enhancers and promoters are important classes of DNA regulatory elements (DREs) that govern gene expression. Identifying them at a genomic scale is a critical task in bioinformatics. The DREs often exhibit unique histone mark binding patterns, which can be captured by high-throughput ChIP-seq experiments. To account for the variations and noises among the binding sites, machine learning models are trained on known enhancer/promoter sites using histone mark ChIP-seq data and predict enhancers/promoters at other genomic regions. To this end, we have developed a highly customizable program named DeepRegFinder, which automates the entire process of data processing, model training, and prediction. We have employed convolutional and recurrent neural networks for model training and prediction. DeepRegFinder further categorizes enhancers and promoters into active and poised states, making it a unique and valuable feature for researchers. Our method demonstrates improved precision and recall in comparison to existing algorithms for enhancer prediction across multiple cell types. Moreover, our pipeline is modular and eliminates the tedious steps involved in preprocessing, making it easier for users to apply on their data quickly. Availability and implementation https://github.com/shenlab-sinai/DeepRegFinder.
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Affiliation(s)
- Aarthi Ramakrishnan
- Friedman Brain Institute and Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States
| | - George Wangensteen
- Department of Computer Science, Brown University, Providence, RI 02912, United States
| | - Sarah Kim
- Cancer Program, Broad Institute, Cambridge, MA 02142, United States
| | - Eric J Nestler
- Friedman Brain Institute and Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States
| | - Li Shen
- Friedman Brain Institute and Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States
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3
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Libbrecht MW, Chan RCW, Hoffman MM. Segmentation and genome annotation algorithms for identifying chromatin state and other genomic patterns. PLoS Comput Biol 2021; 17:e1009423. [PMID: 34648491 PMCID: PMC8516206 DOI: 10.1371/journal.pcbi.1009423] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Segmentation and genome annotation (SAGA) algorithms are widely used to understand genome activity and gene regulation. These algorithms take as input epigenomic datasets, such as chromatin immunoprecipitation-sequencing (ChIP-seq) measurements of histone modifications or transcription factor binding. They partition the genome and assign a label to each segment such that positions with the same label exhibit similar patterns of input data. SAGA algorithms discover categories of activity such as promoters, enhancers, or parts of genes without prior knowledge of known genomic elements. In this sense, they generally act in an unsupervised fashion like clustering algorithms, but with the additional simultaneous function of segmenting the genome. Here, we review the common methodological framework that underlies these methods, review variants of and improvements upon this basic framework, and discuss the outlook for future work. This review is intended for those interested in applying SAGA methods and for computational researchers interested in improving upon them.
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Affiliation(s)
| | - Rachel C. W. Chan
- Department of Computer Science, University of Toronto, Toronto, Canada
- Princess Margaret Cancer Centre, University Health Network, Toronto, Canada
| | - Michael M. Hoffman
- Department of Computer Science, University of Toronto, Toronto, Canada
- Princess Margaret Cancer Centre, University Health Network, Toronto, Canada
- Department of Medical Biophysics, University of Toronto, Toronto, Canada
- Vector Institute for Artificial Intelligence, Toronto, Canada
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4
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Fang K, Li T, Huang Y, Jin VX. NucHMM: a method for quantitative modeling of nucleosome organization identifying functional nucleosome states distinctly associated with splicing potentiality. Genome Biol 2021; 22:250. [PMID: 34446075 PMCID: PMC8390234 DOI: 10.1186/s13059-021-02465-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2020] [Accepted: 08/12/2021] [Indexed: 01/01/2023] Open
Abstract
We develop a novel computational method, NucHMM, to identify functional nucleosome states associated with cell type-specific combinatorial histone marks and nucleosome organization features such as phasing, spacing and positioning. We test it on publicly available MNase-seq and ChIP-seq data in MCF7, H1, and IMR90 cells and identify 11 distinct functional nucleosome states. We demonstrate these nucleosome states are distinctly associated with the splicing potentiality of skipping exons. This advances our understanding of the chromatin function at the nucleosome level and offers insights into the interplay between nucleosome organization and splicing processes.
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Affiliation(s)
- Kun Fang
- Department of Molecular Medicine, UTHSA-UTSA Joint Biomedical Engineering Program, San Antonio, TX, 78229, USA
| | - Tianbao Li
- Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78229, USA
| | - Yufei Huang
- Department of Medicine, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA, 15232, USA
| | - Victor X Jin
- Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78229, USA.
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5
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Savadel SD, Hartwig T, Turpin ZM, Vera DL, Lung PY, Sui X, Blank M, Frommer WB, Dennis JH, Zhang J, Bass HW. The native cistrome and sequence motif families of the maize ear. PLoS Genet 2021; 17:e1009689. [PMID: 34383745 PMCID: PMC8360572 DOI: 10.1371/journal.pgen.1009689] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Accepted: 06/30/2021] [Indexed: 01/22/2023] Open
Abstract
Elucidating the transcriptional regulatory networks that underlie growth and development requires robust ways to define the complete set of transcription factor (TF) binding sites. Although TF-binding sites are known to be generally located within accessible chromatin regions (ACRs), pinpointing these DNA regulatory elements globally remains challenging. Current approaches primarily identify binding sites for a single TF (e.g. ChIP-seq), or globally detect ACRs but lack the resolution to consistently define TF-binding sites (e.g. DNAse-seq, ATAC-seq). To address this challenge, we developed MNase-defined cistrome-Occupancy Analysis (MOA-seq), a high-resolution (< 30 bp), high-throughput, and genome-wide strategy to globally identify putative TF-binding sites within ACRs. We used MOA-seq on developing maize ears as a proof of concept, able to define a cistrome of 145,000 MOA footprints (MFs). While a substantial majority (76%) of the known ATAC-seq ACRs intersected with the MFs, only a minority of MFs overlapped with the ATAC peaks, indicating that the majority of MFs were novel and not detected by ATAC-seq. MFs were associated with promoters and significantly enriched for TF-binding and long-range chromatin interaction sites, including for the well-characterized FASCIATED EAR4, KNOTTED1, and TEOSINTE BRANCHED1. Importantly, the MOA-seq strategy improved the spatial resolution of TF-binding prediction and allowed us to identify 215 motif families collectively distributed over more than 100,000 non-overlapping, putatively-occupied binding sites across the genome. Our study presents a simple, efficient, and high-resolution approach to identify putative TF footprints and binding motifs genome-wide, to ultimately define a native cistrome atlas. Understanding gene regulation remains a central goal of modern biology. Delineating the full set of regulatory DNA elements that orchestrate this regulation requires information at two scales; the broad landscape of accessible chromatin, and the site-specific binding of transcription factors (TFs) at discrete cis-regulatory DNA elements. Here we describe a single assay that uses micrococcal nuclease (MNase) as a structural probe to simultaneously reveal regions of accessible chromatin in addition to high-resolution footprints with signatures of TF-occupied cis-elements. We have used maize developing ear tissue as proof of concept, showing the method detects known TF-binding sites. This genome-wide assay not only defines chromatin landscapes, but crucially enables global discovery and mapping of sequence motifs underlying small footprints of ~30 bp to produce an atlas of candidate TF occupancy.
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Affiliation(s)
- Savannah D. Savadel
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
| | - Thomas Hartwig
- Institute for Molecular Physiologie, Heinrich-Heine-Universität, Düsseldorf, Germany
- Independent research groups, Max Planck Institute for Plant Breeding Research, Cologne, Germany
| | - Zachary M. Turpin
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
| | - Daniel L. Vera
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
| | - Pei-Yau Lung
- Department of Statistics, Florida State University, Tallahassee, Florida, United States of America
| | - Xin Sui
- Department of Statistics, Florida State University, Tallahassee, Florida, United States of America
| | - Max Blank
- Institute for Molecular Physiologie, Heinrich-Heine-Universität, Düsseldorf, Germany
- Independent research groups, Max Planck Institute for Plant Breeding Research, Cologne, Germany
| | - Wolf B. Frommer
- Institute for Molecular Physiologie, Heinrich-Heine-Universität, Düsseldorf, Germany
- Independent research groups, Max Planck Institute for Plant Breeding Research, Cologne, Germany
| | - Jonathan H. Dennis
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
| | - Jinfeng Zhang
- Department of Statistics, Florida State University, Tallahassee, Florida, United States of America
| | - Hank W. Bass
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
- * E-mail:
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6
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Jordan KW, He F, de Soto MF, Akhunova A, Akhunov E. Differential chromatin accessibility landscape reveals structural and functional features of the allopolyploid wheat chromosomes. Genome Biol 2020; 21:176. [PMID: 32684157 PMCID: PMC7368981 DOI: 10.1186/s13059-020-02093-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Accepted: 07/06/2020] [Indexed: 12/19/2022] Open
Abstract
Background Our understanding of how the complexity of the wheat genome influences the distribution of chromatin states along the homoeologous chromosomes is limited. Using a differential nuclease sensitivity assay, we investigate the chromatin states of the coding and repetitive regions of the allopolyploid wheat genome. Results Although open chromatin is found to be significantly enriched around genes, the majority of MNase-sensitive regions are located within transposable elements (TEs). Chromatin of the smaller D genome is more accessible than that of the larger A and B genomes. Chromatin states of different TEs vary among families and are influenced by the TEs’ chromosomal position and proximity to genes. While the chromatin accessibility of genes is influenced by proximity to TEs, and not by their position on the chromosomes, we observe a negative chromatin accessibility gradient along the telomere-centromere axis in the intergenic regions, positively correlated with the distance between genes. Both gene expression levels and homoeologous gene expression bias are correlated with chromatin accessibility in promoter regions. The differential nuclease sensitivity assay accurately predicts previously detected centromere locations. SNPs located within more accessible chromatin explain a higher proportion of genetic variance for a number of agronomic traits than SNPs located within more closed chromatin. Conclusions Chromatin states in the wheat genome are shaped by the interplay of repetitive and gene-encoding regions that are predictive of the functional and structural organization of chromosomes, providing a powerful framework for detecting genomic features involved in gene regulation and prioritizing genomic variation to explain phenotypes.
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Affiliation(s)
- Katherine W Jordan
- Department of Plant Pathology, Kansas State University, Manhattan, KS, USA.,USDA-ARS, Hard Winter Wheat Genetics Research Unit, Manhattan, KS, USA
| | - Fei He
- Department of Plant Pathology, Kansas State University, Manhattan, KS, USA
| | - Monica Fernandez de Soto
- Department of Plant Pathology, Kansas State University, Manhattan, KS, USA.,Integrated Genomics Facility, Kansas State University, Manhattan, KS, USA.,Genomic Sciences Laboratory, North Carolina State University, Raleigh, NC, USA
| | - Alina Akhunova
- Department of Plant Pathology, Kansas State University, Manhattan, KS, USA.,Integrated Genomics Facility, Kansas State University, Manhattan, KS, USA
| | - Eduard Akhunov
- Department of Plant Pathology, Kansas State University, Manhattan, KS, USA.
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7
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Parvathaneni RK, Bertolini E, Shamimuzzaman M, Vera DL, Lung PY, Rice BR, Zhang J, Brown PJ, Lipka AE, Bass HW, Eveland AL. The regulatory landscape of early maize inflorescence development. Genome Biol 2020; 21:165. [PMID: 32631399 PMCID: PMC7336428 DOI: 10.1186/s13059-020-02070-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2019] [Accepted: 06/11/2020] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND The functional genome of agronomically important plant species remains largely unexplored, yet presents a virtually untapped resource for targeted crop improvement. Functional elements of regulatory DNA revealed through profiles of chromatin accessibility can be harnessed for fine-tuning gene expression to optimal phenotypes in specific environments. RESULT Here, we investigate the non-coding regulatory space in the maize (Zea mays) genome during early reproductive development of pollen- and grain-bearing inflorescences. Using an assay for differential sensitivity of chromatin to micrococcal nuclease (MNase) digestion, we profile accessible chromatin and nucleosome occupancy in these largely undifferentiated tissues and classify at least 1.6% of the genome as accessible, with the majority of MNase hypersensitive sites marking proximal promoters, but also 3' ends of maize genes. This approach maps regulatory elements to footprint-level resolution. Integration of complementary transcriptome profiles and transcription factor occupancy data are used to annotate regulatory factors, such as combinatorial transcription factor binding motifs and long non-coding RNAs, that potentially contribute to organogenesis, including tissue-specific regulation between male and female inflorescence structures. Finally, genome-wide association studies for inflorescence architecture traits based solely on functional regions delineated by MNase hypersensitivity reveals new SNP-trait associations in known regulators of inflorescence development as well as new candidates. CONCLUSIONS These analyses provide a comprehensive look into the cis-regulatory landscape during inflorescence differentiation in a major cereal crop, which ultimately shapes architecture and influences yield potential.
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Affiliation(s)
| | | | - Md Shamimuzzaman
- Donald Danforth Plant Science Center, St. Louis, MO 63132 USA
- Current address: USDA-ARS Edward T. Schafer Agricultural Research Center, Fargo, ND 58102 USA
| | - Daniel L. Vera
- The Center for Genomics and Personalized Medicine, Florida State University, Tallahassee, FL 32306 USA
- Current address: Department of Genetics, Harvard Medical School, Boston, MA 02115 USA
| | - Pei-Yau Lung
- Department of Statistics, Florida State University, Tallahassee, FL 32306 USA
| | - Brian R. Rice
- Department of Crop Sciences, University of Illinois Urbana-Champaign, Urbana, IL 61801 USA
| | - Jinfeng Zhang
- Department of Statistics, Florida State University, Tallahassee, FL 32306 USA
| | - Patrick J. Brown
- Department of Plant Sciences, University of California, Davis, CA 95616 USA
| | - Alexander E. Lipka
- Department of Crop Sciences, University of Illinois Urbana-Champaign, Urbana, IL 61801 USA
| | - Hank W. Bass
- Department of Biological Science, Florida State University, Tallahassee, FL 32306 USA
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8
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Turpin ZM, Vera DL, Savadel SD, Lung PY, Wear EE, Mickelson-Young L, Thompson WF, Hanley-Bowdoin L, Dennis JH, Zhang J, Bass HW. Chromatin structure profile data from DNS-seq: Differential nuclease sensitivity mapping of four reference tissues of B73 maize ( Zea mays L). Data Brief 2018; 20:358-363. [PMID: 30175199 PMCID: PMC6117953 DOI: 10.1016/j.dib.2018.08.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 07/12/2018] [Accepted: 08/06/2018] [Indexed: 11/17/2022] Open
Abstract
Presented here are data from Next-Generation Sequencing of differential micrococcal nuclease digestions of formaldehyde-crosslinked chromatin in selected tissues of maize (Zea mays) inbred line B73. Supplemental materials include a wet-bench protocol for making DNS-seq libraries, the DNS-seq data processing pipeline for producing genome browser tracks. This report also includes the peak-calling pipeline using the iSeg algorithm to segment positive and negative peaks from the DNS-seq difference profiles. The data repository for the sequence data is the NCBI SRA, BioProject Accession PRJNA445708.
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Affiliation(s)
- Zachary M. Turpin
- Department of Biological Science, Florida State University, Tallahassee, FL 32306-4295, USA
| | - Daniel L. Vera
- Center for Genomics and Personalized Medicine, Florida State University, Tallahassee, FL, USA
| | - Savannah D. Savadel
- Department of Biological Science, Florida State University, Tallahassee, FL 32306-4295, USA
| | - Pei-Yau Lung
- Department of Statistics, Florida State University, Tallahassee, FL, 32306, USA
| | - Emily E. Wear
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh 27606, USA
| | - Leigh Mickelson-Young
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh 27606, USA
| | - William F. Thompson
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh 27606, USA
| | - Linda Hanley-Bowdoin
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh 27606, USA
| | - Jonathan H. Dennis
- Department of Biological Science, Florida State University, Tallahassee, FL 32306-4295, USA
| | - Jinfeng Zhang
- Department of Statistics, Florida State University, Tallahassee, FL, 32306, USA
| | - Hank W. Bass
- Department of Biological Science, Florida State University, Tallahassee, FL 32306-4295, USA
- Corresponding author.
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