Genomic Organization Research Articles

Haplotype-resolved genome assembly and resequencing provide insights into the origin and breeding of modern rose.

Modern rose (Rosa hybrida) is a recently formed interspecific hybrid and has become one of the most important and widely cultivated ornamentals. Here we report the haplotype-resolved chromosome-scale genome assembly of the tetraploid R. hybrida 'Samantha' ('JACmantha') and a genome variation map of 233 Rosa accessions involving various wild species, and old and modern cultivars. Homologous chromosomes of 'Samantha' exhibit frequent homoeologous exchanges. Population genomic and genomic composition analyses reveal the contributions of wild Rosa species to modern roses and highlight that R. odorata and its derived cultivars are important contributors to modern roses, much like R. chinensis 'Old Blush'. Furthermore, selective sweeps during modern rose breeding associated with major agronomic traits, including continuous and recurrent flowering, double flower, flower senescence and disease resistance, are identified. This study provides insights into the genetic basis of modern rose origin and breeding history, and offers unprecedented genomic resources for rose improvement.

Sequencing of historic samples provides complete coding sequences of chicken calicivirus from the United States.

Here, we report the coding-complete genomic sequences of two chicken caliciviruses from US poultry flocks in 2003 and 2004. They show the same genomic organization as that of other members of the Bavovirus genus and have the highest nucleotide identity (~88%) with strains from clinically normal chickens from Germany in 2004 and Netherlands in 2019.

Compression rates of microbial genomes are associated with genome size and base composition

BackgroundTo what degree a string of symbols can be compressed reveals important details about its complexity. For instance, strings that are not compressible are random and carry a low information potential while the opposite is true for highly compressible strings. We explore to what extent microbial genomes are amenable to compression as they vary considerably both with respect to size and base composition. For instance, microbial genome sizes vary from less than 100,000 base pairs in symbionts to more than 10 million in soil-dwellers. Genomic base composition, often summarized as genomic AT or GC content due to the similar frequencies of adenine and thymine on one hand and cytosine and guanine on the other, also vary substantially; the most extreme microbes can have genomes with AT content below 25% or above 85% AT. Base composition determines the frequency of DNA words, consisting of multiple nucleotides or oligonucleotides, and may therefore also influence compressibility. Using 4,713 RefSeq genomes, we examined the association between compressibility, using both a DNA based- (MBGC) and a general purpose (ZPAQ) compression algorithm, and genome size, AT content as well as genomic oligonucleotide usage variance (OUV) using generalized additive models.ResultsWe find that genome size (p < 0.001) and OUV (p < 0.001) are both strongly associated with genome redundancy for both type of file compressors. The DNA-based MBGC compressor managed to improve compression with approximately 3% on average with respect to ZPAQ. Moreover, MBGC detected a significant (p < 0.001) compression ratio difference between AT poor and AT rich genomes which was not detected with ZPAQ.ConclusionAs lack of compressibility is equivalent to randomness, our findings suggest that smaller and AT rich genomes may have accumulated more random mutations on average than larger and AT poor genomes which, in turn, were significantly more redundant. Moreover, we find that OUV is a strong proxy for genome compressibility in microbial genomes. The ZPAQ compressor was found to agree with the MBGC compressor, albeit with a poorer performance, except for the compressibility of AT-rich and AT-poor/GC-rich genomes.

Complete genomes of two cluster AK Arthrobacter phages isolated from soil samples in Newburgh, NY, United States.

Two phages belonging to Arthrobacter phage cluster AK were isolated from soil samples collected in Newburgh, NY in 2021. Both are lytic with a genome organization typical of siphoviruses except for two genes encoding minor tail proteins with pyocin-knob domains found early in the genome, before the terminase gene.

Drought-responsive dynamics of H3K9ac-marked 3D chromatin interactions are integrated by OsbZIP23-associated super-enhancer-like promoter regions in rice

BackgroundIn response to drought stress (DS), plants undergo complex processes that entail significant transcriptome reprogramming. However, the intricate relationship between the dynamic alterations in the three-dimensional (3D) genome and the modulation of gene co-expression in drought responses remains a relatively unexplored area.ResultsIn this study, we reconstruct high-resolution 3D genome maps based on genomic regions marked by H3K9ac, an active histone modification that dynamically responds to soil water variations in rice. We discover a genome-wide disconnection of 3D genome contact upon DS with over 10,000 chromatin loops lost, which are partially recovered in the subsequent re-watering. Loops integrating promoter–promoter interactions (PPI) contribute to gene expression in addition to basal H3K9ac modifications. Moreover, H3K9ac-marked promoter regions with high affinities in mediating PPIs, termed as super-promoter regions (SPRs), integrate spatially clustered PPIs in a super-enhancer-like manner. Interestingly, the knockout mutation of OsbZIP23, a well-defined DS-responsive transcription factor, leads to the disassociation of over 80% DS-specific PPIs and decreased expression of the corresponding genes under DS. As a case study, we show how OsbZIP23 integrates the PPI cluster formation and the co-expression of four dehydrin genes, RAB16A–D, through targeting the RAB16C SPR in a stress signaling-dependent manner.ConclusionsOur high-resolution 3D genome maps unveil the principles and details of dynamic genome folding in response to water supply variations and illustrate OsbZIP23 as an indispensable integrator of the yet unique 3D genome organization that is essential for gene co-expression under DS in rice.

Hidden evolutionary constraints dictate the retention of coronavirus accessory genes.

Coronaviruses exhibit many mechanisms of genetic innovation, including the acquisition of accessory genes that originate by capture of cellular genes or through duplication of existing viral genes. Accessory genes influence viral host range and cellular tropism, but little is known about how selection acts on these variable regions of virus genomes. We used experimental evolution of mouse hepatitis virus (MHV) encoding a cellular AKAP7 phosphodiesterase and an inactive native phosphodiesterase, NS2 to model the evolutionary fate of accessory genes. After courses of serial infection, the gene encoding inactive NS2, ORF2, unexpectedly remained intact, suggesting it is under cryptic constraint uncoupled from the function of NS2. In contrast, AKAP7 was retained under strong selection but rapidly lost under relaxed selection. Experimental evolution also led to altered viral replication in a cell type-specific manner and changed the relative proportions of subgenomic viral RNA in plaque-purified viral isolates, revealing additional mechanisms of adaptation. Guided by the retention of ORF2 and similar patterns in related betacoronaviruses, we analyzed ORF8 of SARS-CoV-2, which arose via gene duplication and contains premature stop codons in several globally successful lineages. As with MHV ORF2, the coding-defective SARS-CoV-2 ORF8 gene remains largely intact, mirroring patterns observed during MHV experimental evolution, challenging assumptions on the dynamics of gene loss in virus genomes and extending these findings to viruses currently adapting to humans.

Cytogenetic bands and sharp peaks of Alu underlie large-scale segmental regulation of nuclear genome architecture

ABSTRACT Cytogenetic bands reflect genomic organization in large blocks of DNA with similar properties. Because banding patterns are invariant, this organization may often be assumed unimportant for genome regulation. Results here challenge that view. Findings here suggest cytogenetic bands reflect a visible framework upon which regulated genome architecture is built. Given Alu and L1 densities differ in cytogenetic bands, we examined their distribution after X-chromosome inactivation or formation of senescent-associated heterochromatin foci (SAHFs). Alu-rich regions remain outside both SAHFs and the Barr Body (BB), affirming that the BB is not the whole chromosome but a condensed, L1-rich core. Hi-C analysis of senescent cells demonstrates large (~10 Mb) G-bands remodel as a contiguous unit, gaining distal intrachromosomal interactions as syntenic G-bands coalesce into SAHFs. Striking peaks of Alu within R-bands strongly resist condensation. Thus, large-scale segmental genome architectur relates to dark versus light cytogenetic bands and Alu-peaks, implicating both in chromatin regulation.

Genome-wide identification of m6A-related gene family and the involvement of TdFIP37 in salt stress in wild emmer wheat.

The genomic organization, phylogenetic relationship, expression patterns, and genetic variations of m6A-related genes were systematically investigated in wild emmer wheat and the function of TdFIP37 regulating salt tolerance was preliminarily determined. m6A modification is one of the most abundant and crucial RNA modifications in eukaryotics, playing the indispensable role in growth and development as well as stress response in plants. However, its significance in wild emmer wheat remains elusive. Here, a genome-wide search of m6A-related genes was conducted in wild emmer wheat to obtain 64 candidates, including 21 writers, 17 erasers, and 26 readers. Phylogenetic and collinearity analysis demonstrated that segmental duplication and polyploidization contributed mainly to the expansion of m6A-related genes in wild emmer. A number of cis-acting elements involving in stress and hormonal regulation were found in the promoter regions of them, such as MBS, LTR, and ABRE. Genetic variation of them was also investigated using resequencing data and obvious genetic bottleneck was occurred on them during wild emmer wheat domestication process. Furthermore, the salt-responsive candidates were investigated through RNA-seq data and qRT-PCR validation using the salt-tolerant and -sensitive genotypes and the co-expression analysis showed that they played the hub role in regulating salt stress response. Finally, the loss-function mutant of Tdfip37 displayed the significantly higher salt-sensitive compared to WT and then RNA-seq analysis demonstrated that FIP37 mediated the MAPK pathway, hormone signal transduction, as well as transcription factor to regulate salt tolerance. This study provided the potential m6A genes for functional analysis, which will contribute to better understand the regulatory roles of m6A modification and also improve the salt tolerance from the perspective of epigenetic approach in emmer wheat and other crops.

Chromosome-level genome assembly of the sacoglossan sea slug Elysia timida (Risso, 1818)

BackgroundSequencing and annotating genomes of non-model organisms helps to understand genome architecture, the genetic processes underlying species traits, and how these genes have evolved in closely-related taxa, among many other biological processes. However, many metazoan groups, such as the extremely diverse molluscs, are still underrepresented in the number of sequenced and annotated genomes. Although sequencing techniques have recently improved in quality and quantity, molluscs are still neglected due to difficulties in applying standardized protocols for obtaining genomic data.ResultsIn this study, we present the chromosome-level genome assembly and annotation of the sacoglossan sea slug species Elysia timida, known for its ability to store the chloroplasts of its food algae. In particular, by optimizing the long-read and chromosome conformation capture library preparations, the genome assembly was performed using PacBio HiFi and Arima HiC data. The scaffold and contig N50s, at 41.8 Mb and 1.92 Mb, respectively, are approximately 30-fold and fourfold higher compared to other published sacoglossan genome assemblies. Structural annotation resulted in 19,904 protein-coding genes, which are more contiguous and complete compared to publicly available annotations of Sacoglossa with respect to metazoan BUSCOs. We found no evidence for horizontal gene transfer (HGT), i.e. no photosynthetic genes encoded in the sacoglossan nucleus genome. However, we detected genes encoding polyketide synthases in E. timida, indicating that polypropionates are produced. HPLC–MS/MS analysis confirmed the presence of a large number of polypropionates, including known and yet uncharacterised compounds.ConclusionsWe can show that our methodological approach helps to obtain a high-quality genome assembly even for a "difficult-to-sequence" organism, which may facilitate genome sequencing in molluscs. This will enable a better understanding of complex biological processes in molluscs, such as functional kleptoplasty in Sacoglossa, by significantly improving the quality of genome assemblies and annotations.

Metagenomes and metagenome assembled genomes from anaerobic digesters at three Canadian pulp and paper mills.

We present a dataset of six metagenomes and 323 metagenome assembled genomes (MAGs) describing the microbial community of anaerobic digesters at three Canadian pulp and paper mills. Our objective was to assess the coding potential of the microbial community and obtain draft genomes of key organisms in the digesters.

7690 Acute hormonal signaling-induced 3D genome organization controls transcriptional dynamics during adipocyte thermogenesis

Abstract Disclosure: Y. Zhang: None. R. Zheng: None. T. Tsuji: None. Y. Xing: None. C. Wang: None. J. Darcy: None. K. Chen: None. Y. Tseng: None. Brown adipose tissue (BAT) maintains body temperature by dissipating energy as heat, presenting a promising target against obesity and its associated metabolic disorders. When exposed to cold, the β3-adrenergic receptor (β3-AR) in brown adipocytes is stimulated, initiating a sequential signaling cascade and activating a thermogenic gene program essential for heat generation. Despite remarkable progress has been made towards understanding the engagement of transcriptional and epigenetic regulators during thermogenesis in response to β3-AR stimulation, the precise impact of three-dimensional (3D) genome organization, an increasingly important modulator of gene expression, on the activation of thermogenic gene program remains elusive. In this study, we employed high-resolution Micro-C in murine brown adipocytes to interrogate the rapidity of 3D genome reorganization in response to β3-AR hormonal signaling and its impact on transcriptional dynamics during thermogenesis. Our findings unveiled substantial rewiring of chromatin loops within 4 hours of β3-AR stimulation. These dynamic changes in chromatin loops, particularly enhancer-promoter (E-P) interactions, were coupled with gene activation during thermogenesis. Furthermore, we uncovered the mechanisms by which β3-AR hormonal signaling mediates 3D chromatin reorganization to regulate the thermogenic gene program. We found that β3-AR hormonal signaling induced the phosphorylation of p18Hamlet, a subunit of the SRCAP complex, facilitating the deposition of the histone variant H2A.Z into regulatory DNA regions. This nucleosome incorporation of H2A.Z further mediated nucleosome rearrangement, favoring the formation of nucleosome-depleted regions (NDRs) and enhancing the accessibility of regulatory DNA regions. As a result, H2A.Z chromatin incorporation facilitated interactions between cis-regulatory regions and gene promoters, such as E-P interactions, thereby activating thermogenic gene expression in response to β3-AR stimulation. Loss of H2A.Z disrupted loop dynamics, impeding gene activation and BAT thermogenic capacity. The conserved role of H2A.Z in human thermogenesis was validated, and we identified adiposity-related SNPs in human homologous loop anchors that could potentially be targeted for treating obesity. Taken together, our results unveil a previously underappreciated aspect of acute hormonal signaling-induced chromatin dynamics in orchestrating the thermogenic program in brown adipocytes. These findings not only enhance our understanding of molecular regulation of thermogenesis but also shed light on the role of rapid and dynamic chromatin reconfiguration in regulating the cellular response to external stimuli. Our study bridges a critical gap between 3D genome organization and gene activation in the thermogenic program mediated by acute β3-AR hormonal signaling. Presentation: 6/2/2024

Super-resolved analysis of colocalization between replication and transcription along the cell cycle in a model of oncogene activation

To understand how oncogenes affect genome organization, it is essential to visualize fundamental processes such as DNA replication and transcription at high resolution in intact cells. At the same time, it is important to determine the progression of the cell along the cell cycle, as cell cycle regulation is crucial for the control of cell proliferation and oncogenesis. Here, we present a super-resolution imaging-based method to analyze single cell nuclei sorted according to specific phases of the cell cycle. The sorting is based on the evaluation of the number and the intensity of pixels in the replication foci image and the colocalization analysis is based on image cross-correlation spectroscopy (ICCS). We evaluate the colocalization between replication and transcription, at different cell cycle phases, in a model of PML-RARα oncogene activation. We find that colocalization between replication and transcription is higher in cells in early S phase compared to cells in middle and late S phase. When we turn on the PML-RARα oncogene, this colocalization pattern is preserved but we detect an increase of colocalization between replication and transcription in the early S phase which points to an effect of the PML-RARα oncogene on the coordination between replication and transcription.

The mitochondrial genome of Lavandula angustifolia Mill. (Lamiaceae) sheds light on its genome structure and gene transfer between organelles

BackgroundLavandula angustifolia holds importance as an aromatic plant with extensive applications spanning the fragrance, perfume, cosmetics, aromatherapy, and spa sectors. Beyond its aesthetic and sensory applications, this plant offers medicinal benefits as a natural herbal remedy and finds use in household cleaning products. While extensive genomic data, inclusive of plastid and nuclear genomes, are available for this species, researchers have yet to characterize its mitochondrial genome. This gap in knowledge hampers deeper understanding of the genome organization and its evolutionary significance.ResultsThrough the course of this study, we successfully assembled and annotated the mitochondrial genome of L. angustifolia, marking a first in this domain. This assembled genome encompasses 61 genes, which comprise 34 protein-coding genes, 24 transfer RNA genes, and three ribosomal RNA genes. We identified a chloroplast sequence insertion into the mitogenome, which spans a length of 10,645 bp, accounting for 2.94% of the mitogenome size. Within these inserted sequences, there are seven intact tRNA genes (trnH-GUG, trnW-CCA, trnD-GUC, trnS-GGA, trnN-GUU, trnT-GGU, trnP-UGG) and four complete protein-coding genes (psbA, rps15, petL, petG) of chloroplast derivation. Additional discoveries include 88 microsatellites, 15 tandem repeats, 74 palindromic repeats, and 87 forward long repeats. An RNA editing analysis highlighted an elevated count of editing sites in the cytochrome c oxidase genes, notably ccmB with 34 editing sites, ccmFN with 32, and ccmC with 29. All protein-coding genes showed evidence of cytidine-to-uracil conversion. A phylogenetic analysis, utilizing common protein-coding genes from 23 Lamiales species, yielded a tree with consistent topology, supported by high confidence values.ConclusionsAnalysis of the current mitogenome resource revealed its typical circular genome structure. Notably, sequences originally from the chloroplast genome were found within the mitogenome, pointing to the occurrence of horizontal gene transfer between organelles. This assembled mitogenome stands as a valuable resource for subsequent studies on mitogenome structures, their evolution, and molecular biology.

The complete mitochondrial genome of Paraclius curvispinus Yang et Saigusa, 2001 (Diptera: Dolichopodidae)

This study presented the first sequencing and analysis of the mitochondrial genome of Paraclius curvispinus Yang and Saigusa, 2001, a predator fly belonging to the family Dolichopodidae (long-legged fly). The complete mitochondrial genome of P. curvispinus was 16,882 bp long (GenBank accession number: PP498802), which contained 13 protein-coding genes, 22 tRNAs, 2 rRNAs, and a control region. The nucleotide composition of mitochondrial genome of P. curvispinus was 38.48% of A, 36.00% of T, 10.67% of G, and 14.85% of C. Maximum-likelihood (ML) analysis revealed the phylogenetic relationships within the subfamily Dolichopodinae, suggesting the following grouping: ((Dolichopus + Lichtwardtia)+((Hercostomus + Poecilobothrus)+ Gymnopternus))+ Paraclius. This study provides a basis for discussing the evolution of mosquito larval predation habits of Dolichopodinae.

Predicting p53-dependent cell transitions from thermodynamic models.

A cell's fate involves transitions among its various states, each defined by a distinct gene expression profile governed by the topology of gene regulatory networks, which are affected by 3D genome organization. Here, we develop thermodynamic models to determine the fate of a malignant cell as governed by the tumor suppressor p53 signaling network, taking into account long-range chromatin interactions in the mean-field approximation. The tumor suppressor p53 responds to stress by selectively triggering one of the potential transcription programs that influence many layers of cell signaling. These range from p53 phosphorylation to modulation of its DNA binding affinity, phase separation phenomena, and internal connectivity among cell fate genes. We use the minimum free energy of the system as a fundamental property of biological networks that influences the connection between the gene network topology and the state of the cell. We constructed models based on network topology and equilibrium thermodynamics. Our modeling shows that the binding of phosphorylated p53 to promoters of target genes can have properties of a first order phase transition. We apply our model to cancer cell lines ranging from breast cancer (MCF-7), colon cancer (HCT116), and leukemia (K562), with each one characterized by a specific network topology that determines the cell fate. Our results clarify the biological relevance of these mechanisms and suggest that they represent flexible network designs for switching between developmental decisions.

Sequencing and phylogenetic analysis of the complete mitochondrial genome of the Eurasian Harvest Mouse (Micromys minutus) Pallas 1771 from China

This study aimed to examine the complete mitochondrial genome sequence of the Eurasian Harvest Mouse (Micromys minutus) through polymerase chain reaction. The mitochondrial genome of M. minutus was characterized as a circular, double-stranded DNA molecule, encompassing a total length of 16,239 bp. The mitochondrial genome composition of M. minutus was found to include 13 protein-coding genes, a single control region, 22 tRNA genes, 2 rRNA genes, and a origin of L-strand replication. The accurate identification, sequencing, and assembly of the M. minutus mitochondrial genome were successfully conducted in this study, providing a resource for the scientific community to accurately attribute the mitochondrial genome of this species.

Transcription dynamics and genome organization in the mammalian nucleus: Recent advances.

Single-molecule tracking (SMT) has emerged as the dominant technology to investigate the dynamics of chromatin-transcription factor (TF) interactions. How long a TF needs to bind to a regulatory site to elicit a transcriptional response is a fundamentally important question. However, highly divergent estimates of TF binding have been presented in the literature, stemming from differences in photobleaching correction and data analysis. TF movement is often interpreted as specific or non-specific association with chromatin, yet the dynamic nature of the chromatin polymer is often overlooked. In this perspective, we highlight how recent SMT studies have reshaped our understanding of TF dynamics, chromatin mobility, and genome organization in the mammalian nucleus, focusing on the technical details and biological implications of these approaches. In a remarkable convergence of fixed and live-cell imaging, we show how super-resolution and SMT studies of chromatin have dovetailed to provide a convincing nanoscale view of genome organization.

A consequential one-night stand: Episodic historical hybridization leads to mitochondrial takeover in sympatric desert ant-eating spiders

Disentangling the genomic intricacies underlying speciation and the causes of discordance between sources of evidence can offer remarkable insights into evolutionary dynamics. The ant-eating spider Zodarion nitidum, found across the Middle East and Egypt, displays yellowish and blackish morphs that co-occur sympatrically. These morphs additionally differ in behavioral and physiological features and show complete pre-mating reproductive isolation. In contrast, they possess similar sexual features and lack distinct differences in their mitochondrial DNA. We analyzed both Z. nitidum morphs and outgroups using genome-wide and additional mitochondrial DNA data. The genomic evidence indicated that Yellow and Black are reciprocally independent lineages without signs of recent admixture. Interestingly, the sister group of Yellow is not Black but Z. luctuosum, a morphologically distinct species. Genomic gene flow analyses pinpointed an asymmetric nuclear introgression event, with Yellow contributing nearly 5 % of its genome to Black roughly 320,000 years ago, intriguingly aligning with the independently estimated origin of the mitochondrial DNA of Black. We conclude that the blackish and yellowish morphs of Z. nitidum are long-diverged distinct species, and that the ancient and modest genomic introgression event registered resulted in a complete mitochondrial takeover of Black by Yellow. This investigation underscores the profound long-term effects that even modest hybridization events can have on the genome of organisms. It also exemplifies the utility of phylogenetic networks for estimating historical events and how integrating independent lines of evidence can increase the reliability of such estimations.

Genomic Organization and Regulation of Gene Expression in the Distal Convoluted Tubule

Genomic Organization and Regulation of Gene Expression in the Distal Convoluted Tubule

Unravelling Prokaryotic Codon Usage: Insights from Phylogeny, Influencing Factors and Pathogenicity

Analyzing prokaryotic codon usage trends has become a crucial topic of study with significant ramifications for comprehending microbial genetics, classification, evolution, and the control of gene expression. This review study explores the numerous facets of prokaryotic codon usage patterns, looking at different parameters like habitat and lifestyle across broad groups of prokaryotes by emphasizing the role of codon reprogramming in adaptive strategies and its integration into systems biology. We also explored the numerous variables driving codon usage bias, including natural selection, mutation, horizontal gene transfer, codon-anticodon interaction, and genomic composition in prokaryotes through a thorough study of current literature. Furthermore, a special session on codon usage on pathogenic prokaryotes and the role of codon usage in the phylogeny of prokaryotes has been discussed. We also looked at the various software and indices that have been recently applied to prokaryotic genomes. The promising directions that lay ahead to map the future of codon usage research on prokaryotes have been emphasized. Codon usage variations across prokaryotic communities could be better understood by combining environmental, metagenomic, and system biology approaches.