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Asset Tag: Review

July 7, 2019

Completing the human genome: the progress and challenge of satellite DNA assembly.

Genomic studies rely on accurate chromosome assemblies to explore sequence-based models of cell biology, evolution and biomedical disease. However, even the extensively studied human genome has not yet reached a complete, ‘telomere-to-telomere’, chromosome assembly. The largest assembly gaps remain in centromeric regions and acrocentric short arms, sites known to contain megabase-sized arrays of tandem repeats, or satellite DNAs. This review aims to briefly address the progress and challenges of generating correct assemblies of satellite DNA arrays. Although the focus is placed on the human genome, many concepts presented here are applicable to other genomes.

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July 7, 2019

The Brachypodium distachyon reference genome

Grasses provide the bulk of human calories but improvement in grass yields is hindered by the characteristically large and complex genomes of these species; the genomes of wheat, maize, and sugar cane are 17,000, 2300, and 10,000 Mb, respectively. Brachypodium distachyon has one of the smallest genomes of all grasses at 272 Mb, and a number of key traits that make it a good model grass. Brachypodium was the fourth sequenced grass genome, after rice, Sorghum, and maize, and was the first sequenced in the Pooideae subfamily, a diverse group that includes wheat, barley, oat, and rye. The Brachypodium genome was sequenced using a whole genome shotgun approach with Sanger sequencing and is nearly complete with 99.6 % of the sequences anchored to five chromosomes. Sequencing of Brachypodium enabled comparative genomic analysis of grass genomes and shed light on processes involved in chromosome fusions and maintenance of a small genome. The high-quality Brachypodium genome sequence provides a framework for gene expression atlases, resequencing, quantitative trait loci (QTL) mapping, GWAS, and ENCODE datasets. The wealth of Brachypodium genomic resources have cemented its utility as a model organism and will facilitate translational work for improving the grasses that feed the world.

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July 7, 2019

Role of restriction-modification systems in prokaryotic evolution and ecology

Restriction–modification (R-M) systems are able to methylate or cleave DNA depending on methylation status of their recognition site. It allows them to protect bacterial cells from invasion by foreign DNA. Comparative analysis of a large number of available bacterial genomes and methylomes clearly demonstrates that the role of R-M systems in bacteria is wider than only defense. R-M systems maintain heterogeneity of a bacterial population and are involved in adaptation of bacteria to change in their environmental conditions. R-M systems can be essential for host colonization by pathogenic bacteria. Phase variation and intragenomic recombinations are sources of the fast evolution of the specificity of R-M systems. This review focuses on the influence of R-M systems on evolution and ecology of prokaryotes.

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July 7, 2019

DNA N(6)-methyladenine: a new epigenetic mark in eukaryotes?

DNA N(6)-adenine methylation (N(6)-methyladenine; 6mA) in prokaryotes functions primarily in the host defence system. The prevalence and significance of this modification in eukaryotes had been unclear until recently. Here, we discuss recent publications documenting the presence of 6mA in Chlamydomonas reinhardtii, Drosophila melanogaster and Caenorhabditis elegans; consider possible roles for this DNA modification in regulating transcription, the activity of transposable elements and transgenerational epigenetic inheritance; and propose 6mA as a new epigenetic mark in eukaryotes.

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July 7, 2019

Bordetella pertussis evolution in the (functional) genomics era.

The incidence of whooping cough caused by Bordetella pertussis in many developed countries has risen dramatically in recent years. This has been linked to the use of an acellular pertussis vaccine. In addition, it is thought that B. pertussis is adapting under acellular vaccine mediated immune selection pressure, towards vaccine escape. Genomics-based approaches have revolutionized the ability to resolve the fine structure of the global B. pertussis population and its evolution during the era of vaccination. Here, we discuss the current picture of B. pertussis evolution and diversity in the light of the current resurgence, highlight import questions raised by recent studies in this area and discuss the role that functional genomics can play in addressing current knowledge gaps.© FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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July 7, 2019

Twenty years of bacterial genome sequencing.

Twenty years ago, the publication of the first bacterial genome sequence, from Haemophilus influenzae, shook the world of bacteriology. In this Timeline, we review the first two decades of bacterial genome sequencing, which have been marked by three revolutions: whole-genome shotgun sequencing, high-throughput sequencing and single-molecule long-read sequencing. We summarize the social history of sequencing and its impact on our understanding of the biology, diversity and evolution of bacteria, while also highlighting spin-offs and translational impact in the clinic. We look forward to a ‘sequencing singularity’, where sequencing becomes the method of choice for as-yet unthinkable applications in bacteriology and beyond.

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July 7, 2019

Impact of the omic technologies for understanding the modes of action of biological control agents against plant pathogens

The characterization of microbial biological control agents (MBCAs) is crucial to improve their efficacy and consistency as biopesticides. Powerful approaches to characterize MBCA’s modes of action are provided by modern molecular technologies. This paper reviews improvements achieved in this subject by three “omics” approaches: namely the genomic, the transcriptomic and the proteomic approaches. The paper discusses the advantages and drawbacks of new molecular techniques and ‘discovery driven’ approaches to the study of the biocontrol properties against plant pathogens. Omics technologies are capable of: (i) identifying the genome, transcriptome or proteome features of an MBCA strain, (ii) comparing properties of strains/mutants with different biocontrol efficacy, (iii) identifying and characterizing genes, mRNAs and proteins involved in MBCA modes of action, and (iv) simultaneously studying the transcriptome or proteome of the plant host, the plant pathogen and the MBCAs in relation to their bi- or tri-trophic interactions

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July 7, 2019

Botrytis, the good, the bad and the ugly

Botrytis spp. are efficient pathogens, causing devastating diseases and significant crop losses in a wide variety of plant species. Here we outline our review of these pathogens, as well as highlight the major advances of the past 10 years in studying Botrytis in interaction with its hosts. Progress in molecular genetics and the development of relevant phylogenetic markers in particular, has resulted in the characterisation of approximately 30 species. The host range of Botrytis spp. includes plant species that are members of 170 families of cultivated plants.

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July 7, 2019

Current overview on the study of bacteria in the rhizosphere by modern molecular techniques: a mini–review

The rhizosphere (soil zone influenced by roots) is a complex environment that harbors diverse bacterial populations, which have an important role in biogeochemical cycling of organic matter and mineral nutrients. Nevertheless, our knowledge of the ecology and role of these bacteria in the rhizosphere is very limited, particularly regarding how indigenous bacteria are able to communicate, colonize root environments, and compete along the rhizosphere microsites. In recent decades, the development and improvement of molecular techniques have provided more accurate knowledge of bacteria in their natural environment, refining microbial ecology and generating new questions about the roles and functions of bacteria in the rhizosphere. Recently, advances in soil post?genomic techniques (metagenomics, metaproteomics and metatranscriptomics) are being applied to improve our understanding of the microbial communities at a higher resolution. Moreover, advantages and limitations of classical and post?genomic techniques must be considered when studying bacteria in the rhizosphere. This review provides an overview of the current knowledge on the study of bacterial community in the rhizosphere by using modern molecular techniques, describing the bias of classical molecular techniques, next generation sequencing platforms and post?genomics techniques.

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July 7, 2019

Genomics of wood-degrading fungi.

Woody plants convert the energy of the sun into lignocellulosic biomass, which is an abundant substrate for bioenergy production. Fungi, especially wood decayers from the class Agaricomycetes, have evolved ways to degrade lignocellulose into its monomeric constituents, and understanding this process may facilitate the development of biofuels. Over the past decade genomics has become a powerful tool to study the Agaricomycetes. In 2004 the first sequenced genome of the white rot fungus Phanerochaete chrysosporium revealed a rich catalog of lignocellulolytic enzymes. In the decade that followed the number of genomes of Agaricomycetes grew to more than 75 and revealed a diversity of wood-decaying strategies. New technologies for high-throughput functional genomics are now needed to further study these organisms. Copyright © 2014 Elsevier Inc. All rights reserved.

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July 7, 2019

The characterization of goat genetic diversity: Towards a genomic approach

The investigation of genetic diversity at molecular level has been proposed as a valuable complement and sometimes proxy to phenotypic diversity of local breeds and is presently considered as one of the FAO priorities for breed characterization. By recommending a set of selected molecular markers for each of the main livestock species, FAO has promoted the meta-analysis of local datasets, to achieve a global view of molecular genetic diversity. Analysis within the EU Globaldiv project of two large goat microsatellite datasets produced by the Econogene Consortium and the IAEA CRP–Asia Consortium, respectively, has generated a picture of goat diversity across continents. This indicates a gradient of decreasing diversity from the domestication centre towards Europe and Asia, a clear phylogeographic structure at the continental and regional levels, and in Asia a limited genetic differentiation among local breeds. The development of SNP panels that assay thousands of markers and the whole genome sequencing of livestock permit an affordable use of genomic technologies in all livestock species, goats included. Preliminary data from the Italian Goat Consortium indicate that the SNP panel developed for this species is highly informative. The existing panel can be improved by integrating additional SNPs identified from the whole genome sequence alignment of goats adapted to extreme climates. Part of this effort is being achieved by international projects (e.g. EU FP7 NextGen and 3SR projects), but a fair representation of the global diversity in goats requires a large panel of samples (i.e. as in the recently launched 1000 cattle genomes initiative). Genomic technologies offer new strategies to investigate complex traits difficult to measure. For example, the comparison of patterns of diversity among the genomes in selected groups of animals (e.g. adapted to different environments) and the integration of genome-wide diversity with new GIScience-based methods are able to identify molecular markers associated with genomic regions of putative importance in adaptation and thus pave the way for the identification of causative genes. Goat breeds adapted to different production systems in extreme and harsh environments will play an important role in this process. The new sequencing technologies also permit the analysis of the entire mitochondrial genome at maximum resolution. The complete mtDNA sequence is now the common standard format for the investigation of human maternal lineages. A preliminary analysis of the complete goat mtDNA genome supports a single Neolithic origin of domestic goats rather than multiple domestication events in different geographic areas.

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July 7, 2019

Enhancing single-molecule fluorescence with nanophotonics.

Single-molecule fluorescence spectroscopy has become an important research tool in the life sciences but a number of limitations hinder the widespread use as a standard technique. The limited dynamic concentration range is one of the major hurdles. Recent developments in the nanophotonic field promise to alleviate these restrictions to an extent that even low affinity biomolecular interactions can be studied. After motivating the need for nanophotonics we introduce the basic concepts of nanophotonic devices such as zero mode waveguides and nanoantennas. We highlight current applications and the future potential of nanophotonic approaches when combined with biological systems and single-molecule spectroscopy. Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

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July 7, 2019

The challenges and importance of structural variation detection in livestock.

Recent studies in humans and other model organisms have demonstrated that structural variants (SVs) comprise a substantial proportion of variation among individuals of each species. Many of these variants have been linked to debilitating diseases in humans, thereby cementing the importance of refining methods for their detection. Despite progress in the field, reliable detection of SVs still remains a problem even for human subjects. Many of the underlying problems that make SVs difficult to detect in humans are amplified in livestock species, whose lower quality genome assemblies and incomplete gene annotation can often give rise to false positive SV discoveries. Regardless of the challenges, SV detection is just as important for livestock researchers as it is for human researchers, given that several productive traits and diseases have been linked to copy number variations (CNVs) in cattle, sheep, and pig. Already, there is evidence that many beneficial SVs have been artificially selected in livestock such as a duplication of the agouti signaling protein gene that causes white coat color in sheep. In this review, we will list current SV and CNV discoveries in livestock and discuss the problems that hinder routine discovery and tracking of these polymorphisms. We will also discuss the impacts of selective breeding on CNV and SV frequencies and mention how SV genotyping could be used in the future to improve genetic selection.

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July 7, 2019

The first 50 plant genomes

Fifty-five plant genomes have been published to date representing 49 different species (Table 1 includes PubMed IDs for complete reference). What have we learned from the first wave of plant genomes? It has been said that plant genome papers (and genome papers in general) are dry and lack “biology” and that the days of high impact plant genome papers are drawing to a close unless they explore significant biology. However, with each new genome, earlier observations are refined and plant genome papers continue to reveal novel aspects of genome biology. For example, the tomato and banana genome papers refined current thinking on the whole genome duplications (WGD) that shaped dicot and monocot genome evolution (D’Hont et al., 2012; Tomato Genome Consortium, 2012). These observations were enabled not only by high quality genome assemblies but also by a greater number of genomes available for com- parisons. In addition, the initial round of plant genomes enabled the first generation of functional genomics that helped to define the roles of hundreds of genes, provided unprecedented access to sequence-based markers for breeding, and provided glimpses into plant evolutionary history. More genomes, representing the diverse array of species in Viridiplantae are still required to gain a full understanding of plant genome structure, evolution, and complexity.

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