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Emerging evidence reveals that the three-dimensional (3D) chromatin architecture plays a key regulatory role in various biological processes of plants. However, information on the 3D chromatin architecture of the legume model plant Medicago truncatula and its potential roles in the regulation of response to mineral nutrient deficiency are very limited. Using high-resolution chromosome conformation capture sequencing, we identified the 3D genome structure of M. truncatula in terms of A/B compartments, topologically associated domains (TADs) and chromatin loops. The gene density, expressional level, and active histone modification were higher in A compartments than in B compartments. Moreover, we analysed the 3D chromatin architecture reorganization in response to phosphorus (P) deficiency. The intra-chromosomal cis-interaction proportion was increased by P deficiency, and a total of 748 A/B compartment switch regions were detected. In these regions, density changes in H3K4me3 and H3K27ac modifications were associated with expression of P deficiency-responsive genes involved in root system architecture and hormonal responses. Furthermore, these genes enhanced P uptake and mobilization by increasing root surface area and strengthening signal transduction under P deficiency. These findings advance our understanding of the potential roles of 3D chromatin architecture in responses of plants in general, and in particular in M. truncatula, to P deficiency., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Chromatin interactions play essential roles in chromatin conformation and gene expression. However, few tools exist to analyze the spatial density of regulatory chromatin interactions (SD-RCI). Here, we present the multi-modal network (MINE) toolkit, including MINE-Loop, MINE-Density, and MINE-Viewer. The MINE-Loop network aims to enhance the detection of RCIs, MINE-Density quantifies the SD--RCI, and MINE-Viewer facilitates 3D visualization of the density of chromatin interactions and participating regulatory factors (e.g., transcription factors). We applied MINE to investigate the relationship between the SD-RCI and chromatin volume change in HeLa cells before and after liquid-liquid phase separation. Changes in SD-RCI before and after treating the HeLa cells with 1,6-hexanediol suggest that changes in chromatin organization was related to the degree of activation or repression of genes. Together, the MINE toolkit enables quantitative studies on different aspects of chromatin conformation and regulatory activity., Competing Interests: The authors declare no competing interests., (© 2022 The Authors.)

Maize is a model plant species often used for genetics and genomics research because of its genetic diversity. There are prominent morphological, genetic, and epigenetic variations between tropical and temperate maize lines. However, the genome-wide chromatin conformations of these two maize types remain unexplored. We applied a Hi-C approach to compare the genome-wide chromatin interactions between temperate inbred line D132 and tropical line CML288. A reconstructed maize three-dimensional genome model revealed the spatial segregation of the global A and B compartments. The A compartments contain enriched genes and active epigenome marks, whereas the B compartments are gene-poor, transcriptionally silent chromatin regions. Whole-genome analyses indicated that the global A compartment content of CML288 was 3.12% lower than that of D132. Additionally, global and A/B sub-compartments were associated with differential gene expression and epigenetic changes between two inbred lines. About 25.3% of topologically associating domains (TADs) were determined to be associated with complex domain-level modifications that induced transcriptional changes, indicative of a large-scale reorganization of chromatin structures between the inbred maize lines. Furthermore, differences in chromatin interactions between the two lines correlated with epigenetic changes. These findings provide a solid foundation for the wider plant community to further investigate the genome-wide chromatin structures in other plant species., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The non-random spatial packing of chromosomes in the nucleus plays a critical role in orchestrating gene expression and genome function. Here, we present a Hi-C analysis of the chromatin interaction patterns in rice (Oryza sativa L.) at hierarchical architectural levels. We confirm that rice chromosomes occupy their own territories with certain preferential inter-chromosomal associations. Moderate compartment delimitation and extensive TADs (Topologically Associated Domains) were determined to be associated with heterogeneous genomic compositions and epigenetic marks in the rice genome. We found subtle features including chromatin loops, gene loops, and off-/near-diagonal intensive interaction regions. Gene chromatin loops associated with H3K27me3 could be positively involved in gene expression. In addition to insulated enhancing effects for neighbor gene expression, the identified rice gene loops could bi-directionally (+/-) affect the expression of looped genes themselves. Finally, web-interleaved off-diagonal IHIs/KEEs (Interactive Heterochromatic Islands or KNOT ENGAGED ELEMENTs) could trap transposable elements (TEs) via the enrichment of silencing epigenetic marks. In parallel, the near-diagonal FIREs (Frequently Interacting Regions) could positively affect the expression of involved genes. Our results suggest that the chromatin packing pattern in rice is generally similar to that in Arabidopsis thaliana but with clear differences at specific structural levels. We conclude that genomic composition, epigenetic modification, and transcriptional activity could act in combination to shape global and local chromatin packing in rice. Our results confirm recent observations in rice and A. thaliana but also provide additional insights into the patterns and features of chromatin organization in higher plants., (© 2018 The Authors. The Plant Journal published by John Wiley & Sons Ltd and Society for Experimental Biology.)

Background: Root development and function have central roles in plant adaptation to the environment. The modification of root traits has additionally been a major driver of crop performance since the green revolution; however, the molecular underpinnings and the regulatory programmes defining root development and response to environmental stress remain largely unknown. Single-cell reconstruction of gene regulatory programmes provides an important tool to understand the cellular phenotypic variation in complex tissues and their response to endogenous and environmental stimuli. While single-cell transcriptomes of several plant organs have been elucidated, the underlying chromatin landscapes associated with cell type-specific gene expression remain largely unexplored. Results: To comprehensively delineate chromatin accessibility during root development of an important crop, we applied single-cell ATAC-seq (scATAC-seq) to 46,758 cells from rice root tips under normal and heat stress conditions. Our data revealed cell type-specific accessibility variance across most of the major cell types and allowed us to identify sets of transcription factors which associate with accessible chromatin regions (ACRs). Using root hair differentiation as a model, we demonstrate that chromatin and gene expression dynamics during cell type differentiation correlate in pseudotime analyses. In addition to developmental trajectories, we describe chromatin responses to heat and identify cell type-specific accessibility changes to this key environmental stimulus. Conclusions: We report chromatin landscapes during rice root development at single-cell resolution. Our work provides a framework for the integrative analysis of regulatory dynamics in this important crop organ at single-cell resolution. [ABSTRACT FROM AUTHOR]

Structural variations (SVs) are the greatest source of variations in the genome and can lead to oncogenesis. However, the identification and interpretation of SVs in human cancer remain technologically challenging. Here, long‐read sequencing is first employed to depict the signatures of structural variations in carcinogenesis of human pancreatic ductal epithelium. Then widespread reprogramming of the 3D chromatin architecture is revealed by an in situ Hi‐C technique. Integrative analyses indicate that the distribution pattern of SVs among the 3D genome is highly cell‐type specific and the bulk remodeling effects of SVs in the chromatin organization partly depend on intercellular genomic heterogeneity. Meanwhile, contact domains tend to minimize these disrupting effects of SVs within local adjacent genomic regions to maintain overall stability. Notably, complex genomic rearrangements involving two key driver genes CDKN2A and SMAD4 are identified, and their influence on the expression of oncogenes MIR31HG, MYO5B, etc., are further elucidated from both a linear view and 3D perspective. Overall, this work provides a genome‐wide resource and highlights the impact, complexity, and dynamicity of the interplay between structural variations and high‐order chromatin organization, which expands the current understanding of the pathogenesis of SVs in human cancer. [ABSTRACT FROM AUTHOR]

[Display omitted] • A site-specific HPV16 gene knock-in cell model was established. • PIBF1 was up-regulated as cis -perturbation of HPV integration. • PIBF1 is a chromatin binding protein and could interact with cohesin complex off the chromatin. • PIBF1 may cause dysregulation of tumorigenesis-related genes through destroying cohesin ring-shaped structure. Human papillomavirus (HPV) integration can induce gene expression dysregulation by destroying higher-order chromatin structure in cervical cancer. We established a 13q22 site-specific HPV16 gene knock-in cell model to interrogate the changes in chromatin structure at the initial stages of host cell malignant transformation. We designed a CRISPR-Cas9 system with sgRNA targeting 13q22 site and constructed the HPV16 gene donor. Cells were cotransfected, screened, and fluorescence sorted. The whole genome sequencing (WGS) was used to confirm the precise HPV16 gene integration site. Western blot and qRT-PCR were used to measure gene expression. In vitro and in vivo analysis were performed to estimate the tumorigenic potential of the HPV16 knock-in cell model. Combined Hi-C, chromatin immunoprecipitation and RNA sequencing analyses revealed correlations between chromatin structure and gene expression. We performed a coimmunoprecipitation assay with anti-PIBF1 antibody to identify endogenous interacting proteins. In vivo analysis was used to determine the role of PIBF1 in the tumor growth of cervical cancer cells. We successfully established a 13q22 site-specific HPV16 gene knock-in cell model. We found that HPV integration promoted cell proliferation, invasion and stratified growth in vitro, and monoclonal proliferation in vivo. HPV integration divided the affected topologically associated domain (TAD) into two smaller domains, and the progesterone-induced blocking factor 1 (PIBF1) gene near the integration site was upregulated, although PIBF1 was not enriched at the domain boundary by CUT-Tag signal analysis. Moreover, PIBF1 was found to interact with the cohesin complex off chromatin to reduce contact domain formation by disrupting the cohesin ring-shaped structure, causing dysregulation of tumorigenesis-related genes. Xenograft experiments determined the role of PIBF1 in the proliferation in cervical cancer cells. We highlight that PIBF1, a potential chromatin structure regulatory protein, is activated by HPV integration, which provides new insights into HPV integration-driven cervical carcinogenesis. [ABSTRACT FROM AUTHOR]