Menu

Auto Tag: Gene expression

April 21, 2020

Effector gene reshuffling involves dispensable mini-chromosomes in the wheat blast fungus.

Newly emerged wheat blast disease is a serious threat to global wheat production. Wheat blast is caused by a distinct, exceptionally diverse lineage of the fungus causing rice blast disease. Through sequencing a recent field isolate, we report a reference genome that includes seven core chromosomes and mini-chromosome sequences that harbor effector genes normally found on ends of core chromosomes in other strains. No mini-chromosomes were observed in an early field strain, and at least two from another isolate each contain different effector genes and core chromosome end sequences. The mini-chromosome is enriched in transposons occurring most frequently at core chromosome ends. Additionally, transposons in mini-chromosomes lack the characteristic signature for inactivation by repeat-induced point (RIP) mutation genome defenses. Our results, collectively, indicate that dispensable mini-chromosomes and core chromosomes undergo divergent evolutionary trajectories, and mini-chromosomes and core chromosome ends are coupled as a mobile, fast-evolving effector compartment in the wheat pathogen genome.

Read more
April 21, 2020

Recurrent gene co-amplification on Drosophila X and Y chromosomes.

Y chromosomes often contain amplified genes which can increase dosage of male fertility genes and counteract degeneration via gene conversion. Here we identify genes with increased copy number on both X and Y chromosomes in various species of Drosophila, a pattern that has previously been associated with sex chromosome drive involving the Slx and Sly gene families in mice. We show that recurrent X/Y co-amplification appears to be an important evolutionary force that has shaped gene content evolution of sex chromosomes in Drosophila. We demonstrate that convergent acquisition and amplification of testis expressed gene families are common on Drosophila sex chromosomes, and especially on recently formed ones, and we carefully characterize one putative novel X/Y co-amplification system. We find that co-amplification of the S-Lap1/GAPsec gene pair on both the X and the Y chromosome occurred independently several times in members of the D. obscura group, where this normally autosomal gene pair is sex-linked due to a sex chromosome-autosome fusion. We explore several evolutionary scenarios that would explain this pattern of co-amplification. Investigation of gene expression and short RNA profiles at the S-Lap1/GAPsec system suggest that, like Slx/Sly in mice, these genes may be remnants of a cryptic sex chromosome drive system, however additional transgenic experiments will be necessary to validate this model. Regardless of whether sex chromosome drive is responsible for this co-amplification, our findings suggest that recurrent gene duplications between X and Y sex chromosomes could have a widespread effect on genomic and evolutionary patterns, including the epigenetic regulation of sex chromosomes, the distribution of sex-biased genes, and the evolution of hybrid sterility.

Read more
April 21, 2020

Intercellular communication is required for trap formation in the nematode-trapping fungus Duddingtonia flagrans.

Nematode-trapping fungi (NTF) are a large and diverse group of fungi, which may switch from a saprotrophic to a predatory lifestyle if nematodes are present. Different fungi have developed different trapping devices, ranging from adhesive cells to constricting rings. After trapping, fungal hyphae penetrate the worm, secrete lytic enzymes and form a hyphal network inside the body. We sequenced the genome of Duddingtonia flagrans, a biotechnologically important NTF used to control nematode populations in fields. The 36.64 Mb genome encodes 9,927 putative proteins, among which are more than 638 predicted secreted proteins. Most secreted proteins are lytic enzymes, but more than 200 were classified as small secreted proteins (< 300 amino acids). 117 putative effector proteins were predicted, suggesting interkingdom communication during the colonization. As a first step to analyze the function of such proteins or other phenomena at the molecular level, we developed a transformation system, established the fluorescent proteins GFP and mCherry, adapted an assay to monitor protein secretion, and established gene-deletion protocols using homologous recombination or CRISPR/Cas9. One putative virulence effector protein, PefB, was transcriptionally induced during the interaction. We show that the mature protein is able to be imported into nuclei in Caenorhabditis elegans cells. In addition, we studied trap formation and show that cell-to-cell communication is required for ring closure. The availability of the genome sequence and the establishment of many molecular tools will open new avenues to studying this biotechnologically relevant nematode-trapping fungus.

Read more
April 21, 2020

DNA methylation from a Type I restriction modification system influences gene expression and virulence in Streptococcus pyogenes.

DNA methylation is pervasive across all domains of life. In bacteria, the presence of N6-methyladenosine (m6A) has been detected among diverse species, yet the contribution of m6A to the regulation of gene expression is unclear in many organisms. Here we investigated the impact of DNA methylation on gene expression and virulence within the human pathogen Streptococcus pyogenes, or Group A Streptococcus. Single Molecule Real-Time sequencing and subsequent methylation analysis identified 412 putative m6A sites throughout the 1.8 Mb genome. Deletion of the Restriction, Specificity, and Methylation gene subunits (?RSM strain) of a putative Type I restriction modification system lost all detectable m6A at the recognition sites and failed to prevent transformation with foreign-methylated DNA. RNA-sequencing identified 20 genes out of 1,895 predicted coding regions with significantly different gene expression. All of the differentially expressed genes were down regulated in the ?RSM strain relative to the parent strain. Importantly, we found that the presence of m6A DNA modifications affected expression of Mga, a master transcriptional regulator for multiple virulence genes, surface adhesins, and immune-evasion factors in S. pyogenes. Using a murine subcutaneous infection model, mice infected with the ?RSM strain exhibited an enhanced host immune response with larger skin lesions and increased levels of pro-inflammatory cytokines compared to mice infected with the parent or complemented mutant strains, suggesting alterations in m6A methylation influence virulence. Further, we found that the ?RSM strain showed poor survival within human neutrophils and reduced adherence to human epithelial cells. These results demonstrate that, in addition to restriction of foreign DNA, gram-positive bacteria also use restriction modification systems to regulate the expression of gene networks important for virulence.

Read more
April 21, 2020

Finding the needle in a haystack: Mapping antifungal drug resistance in fungal pathogen by genomic approaches.

Fungi are ubiquitous on earth and are essential for the maintenance of the global ecological equilibrium. Despite providing benefits to living organisms, they can also target specific hosts and inflict damage. These fungal pathogens are known to affect, for example, plants and mam- mals and thus reduce crop production necessary to sustain food supply and cause mortality in humans and animals. Designing defenses against these fungi is essential for the control of food resources and human health. As far as fungal pathogens are concerned, the principal option has been the use of antifungal agents, also called fungicides when they are used in the environment.

Read more
April 21, 2020

Anthropogenic N deposition, fungal gene expression, and an increasing soil carbon sink in the Northern Hemisphere.

Terrestrial ecosystems in the Northern Hemisphere are a globally important sink for anthropogenic CO2 in the Earth’s atmosphere, slowing its accumulation as well as the pace of climate warming. With the use of a long-term field experiment (ca. 20 yr), we show that the expression of fungal class II peroxidase genes, which encode enzymes mediating the rate-limiting step of organic matter decay, are significantly downregulated (-60 to -80%) because of increases in anthropogenic N deposition; this response was consistent with a decline in extracellular peroxidase enzyme activity in soil, the slowing of organic-matter decay, and greater soil C storage. The reduction in peroxidase expression we document here occurred in the absence of a compositional shift in metabolically active fungi, indicating that an overall reduction in peroxidase expression underlies the slowing of decay and increases in soil C storage. This molecular mechanism has global implications for soil C storage and should be represented in coupled climate-biogeochemical models simulating the influence of enhanced terrestrial C storage on atmospheric CO2 and the future climate of an N-enriched Earth. © 2019 by the Ecological Society of America.

Read more
April 21, 2020

Genome-Wide Screening for Enteric Colonization Factors in Carbapenem-Resistant ST258 Klebsiella pneumoniae.

A diverse, antibiotic-naive microbiota prevents highly antibiotic-resistant microbes, including carbapenem-resistant Klebsiella pneumoniae (CR-Kp), from achieving dense colonization of the intestinal lumen. Antibiotic-mediated destruction of the microbiota leads to expansion of CR-Kp in the gut, markedly increasing the risk of bacteremia in vulnerable patients. While preventing dense colonization represents a rational approach to reduce intra- and interpatient dissemination of CR-Kp, little is known about pathogen-associated factors that enable dense growth and persistence in the intestinal lumen. To identify genetic factors essential for dense colonization of the gut by CR-Kp, we constructed a highly saturated transposon mutant library with >150,000 unique mutations in an ST258 strain of CR-Kp and screened for in vitro growth and in vivo intestinal colonization in antibiotic-treated mice. Stochastic and partially reversible fluctuations in the representation of different mutations during dense colonization revealed the dynamic nature of intestinal microbial populations. We identified genes that are crucial for early and late stages of dense gut colonization and confirmed their role by testing isogenic mutants in in vivo competition assays with wild-type CR-Kp Screening of the transposon library also identified mutations that enhanced in vivo CR-Kp growth. These newly identified colonization factors may provide novel therapeutic opportunities to reduce intestinal colonization by CR-KpIMPORTANCEKlebsiella pneumoniae is a common cause of bloodstream infections in immunocompromised and hospitalized patients, and over the last 2 decades, some strains have acquired resistance to nearly all available antibiotics, including broad-spectrum carbapenems. The U.S. Centers for Disease Control and Prevention has listed carbapenem-resistant K. pneumoniae (CR-Kp) as an urgent public health threat. Dense colonization of the intestine by CR-Kp and other antibiotic-resistant bacteria is associated with an increased risk of bacteremia. Reducing the density of gut colonization by CR-Kp is likely to reduce their transmission from patient to patient in health care facilities as well as systemic infections. How CR-Kp expands and persists in the gut lumen, however, is poorly understood. Herein, we generated a highly saturated mutant library in a multidrug-resistant K. pneumoniae strain and identified genetic factors that are associated with dense gut colonization by K. pneumoniae This study sheds light on host colonization by K. pneumoniae and identifies potential colonization factors that contribute to high-density persistence of K. pneumoniae in the intestine. Copyright © 2019 Jung et al.

Read more
April 21, 2020

Comprehensive transcriptome analysis reveals genes potentially involved in isoflavone biosynthesis in Pueraria thomsonii Benth.

Pueraria thomsonii Benth is an important medicinal plant. Transcriptome sequencing, unigene assembly, the annotation of transcripts and the study of gene expression profiles play vital roles in gene function research. However, the full-length transcriptome of P. thomsonii remains unknown. Here, we obtained 44,339 nonredundant transcripts of P. thomsonii by using the PacBio RS II Isoform and Illumina sequencing platforms, of which 43,195 were annotated genes. Compared with the expression levels in the plant roots, those of transcripts with a |fold change| = 4 and FDR < 0.01 in the leaves or stems were assigned as differentially expressed transcripts (DETs). In total, we found 9,225 DETs, 32 of which came from structural genes that were potentially involved in isoflavone biosynthesis. The expression profiles of 8 structural genes from the RNA-Seq data were validated by qRT-PCR. We identified 437 transcription factors (TFs) that were positively or negatively correlated with at least 1 of the structural genes involved in isoflavone biosynthesis using Pearson correlation coefficients (r) (r > 0.8 or r < -0.8). We also identified a total of 32 microRNAs (miRNAs), which targeted 805 transcripts. These miRNAs caused enriched function in 'ATP binding', 'defense response', 'ADP binding', and 'signal transduction'. Interestingly, MIR156a potentially promoted isoflavone biosynthesis by repressing SBP, and MIR319 promoted isoflavone biosynthesis by repressing TCP and HB-HD-ZIP. Finally, we identified 2,690 alternative splicing events, including that of the structural genes of trans-cinnamate 4-monooxygenase and pullulanase, which are potentially involved in the biosynthesis of isoflavone and starch, respectively, and of three TFs potentially involved in isoflavone biosynthesis. Together, these results provide us with comprehensive insight into the gene expression and regulation of P. thomsonii.

Read more
April 21, 2020

A chromosome-level sequence assembly reveals the structure of the Arabidopsis thaliana Nd-1 genome and its gene set.

In addition to the BAC-based reference sequence of the accession Columbia-0 from the year 2000, several short read assemblies of THE plant model organism Arabidopsis thaliana were published during the last years. Also, a SMRT-based assembly of Landsberg erecta has been generated that identified translocation and inversion polymorphisms between two genotypes of the species. Here we provide a chromosome-arm level assembly of the A. thaliana accession Niederzenz-1 (AthNd-1_v2c) based on SMRT sequencing data. The best assembly comprises 69 nucleome sequences and displays a contig length of up to 16 Mbp. Compared to an earlier Illumina short read-based NGS assembly (AthNd-1_v1), a 75 fold increase in contiguity was observed for AthNd-1_v2c. To assign contig locations independent from the Col-0 gold standard reference sequence, we used genetic anchoring to generate a de novo assembly. In addition, we assembled the chondrome and plastome sequences. Detailed analyses of AthNd-1_v2c allowed reliable identification of large genomic rearrangements between A. thaliana accessions contributing to differences in the gene sets that distinguish the genotypes. One of the differences detected identified a gene that is lacking from the Col-0 gold standard sequence. This de novo assembly extends the known proportion of the A. thaliana pan-genome.

Read more
April 21, 2020

A whole genome scan of SNP data suggests a lack of abundant hard selective sweeps in the genome of the broad host range plant pathogenic fungus Sclerotinia sclerotiorum.

The pathogenic fungus Sclerotinia sclerotiorum infects over 600 species of plant. It is present in numerous environments throughout the world and causes significant damage to many agricultural crops. Fragmentation and lack of gene flow between populations may lead to population sub-structure. Within discrete recombining populations, positive selection may lead to a ‘selective sweep’. This is characterised by an increase in frequency of a favourable allele leading to reduction in genotypic diversity in a localised genomic region due to the phenomenon of genetic hitchhiking. We aimed to assess whether isolates of S. sclerotiorum from around the world formed genotypic clusters associated with geographical origin and to determine whether signatures of population-specific positive selection could be detected. To do this, we sequenced the genomes of 25 isolates of S. sclerotiorum collected from four different continents-Australia, Africa (north and south), Europe and North America (Canada and the northen United States) and conducted SNP based analyses of population structure and selective sweeps. Among the 25 isolates, there was evidence for two major population clusters. One of these consisted of 11 isolates from Canada, the USA and France (population 1), and the other consisted of nine isolates from Australia and one from Morocco (population 2). The rest of the isolates were genotypic outliers. We found that there was evidence of outcrossing in these two populations based on linkage disequilibrium decay. However, only a single candidate selective sweep was observed, and it was present in population 2. This sweep was close to a Major Facilitator Superfamily transporter gene, and we speculate that this gene may have a role in nutrient uptake from the host. The low abundance of selective sweeps in the S. sclerotiorum genome contrasts the numerous examples in the genomes of other fungal pathogens. This may be a result of its slow rate of evolution and low effective recombination rate due to self-fertilisation and vegetative reproduction.

Read more
April 21, 2020

Comparative genomic analysis of eight novel haloalkaliphilic bacteriophages from Lake Elmenteita, Kenya.

We report complete genome sequences of eight bacteriophages isolated from Haloalkaline Lake Elmenteita found on the floor of Kenyan Rift Valley. The bacteriophages were sequenced, annotated and a comparative genomic analysis using various Bioinformatics tools carried out to determine relatedness of the bacteriophages to each other, and to those in public databases. Basic genome properties like genome size, percentage coding density, number of open reading frames, percentage GC content and gene organizations revealed the bacteriophages had no relationship to each other. Comparison to other nucleotide sequences in GenBank database showed no significant similarities hence novel. At the amino acid level, phages of our study revealed mosaicism to genes with conserved domains to already described phages. Phylogenetic analyses of large terminase gene responsible for DNA packaging and DNA polymerase gene for replication further showed diversity among the bacteriophages. Our results give insight into diversity of bacteriophages in Lake Elmenteita and provide information on their evolution. By providing primary sequence information, this study not only provides novel sequences for biotechnological exploitation, but also sets stage for future studies aimed at better understanding of virus diversity and genomes from haloalkaline lakes in the Rift Valley.

Read more
April 21, 2020

Parallels between natural selection in the cold-adapted crop-wild relative Tripsacum dactyloides and artificial selection in temperate adapted maize.

Artificial selection has produced varieties of domesticated maize that thrive in temperate climates around the world. However, the direct progenitor of maize, teosinte, is indigenous only to a relatively small range of tropical and subtropical latitudes and grows poorly or not at all outside of this region. Tripsacum, a sister genus to maize and teosinte, is naturally endemic to the majority of areas in the western hemisphere where maize is cultivated. A full-length reference transcriptome for Tripsacum dactyloides generated using long-read Iso-Seq data was used to characterize independent adaptation to temperate climates in this clade. Genes related to phospholipid biosynthesis, a critical component of cold acclimation in other cold-adapted plant lineages, were enriched among those genes experiencing more rapid rates of protein sequence evolution in T. dactyloides. In contrast with previous studies of parallel selection, we find that there is a significant overlap between the genes that were targets of artificial selection during the adaptation of maize to temperate climates and those that were targets of natural selection in temperate-adapted T. dactyloides. Genes related to growth, development, response to stimulus, signaling, and organelles were enriched in the set of genes identified as both targets of natural and artificial selection. © 2019 The Authors The Plant Journal © 2019 John Wiley & Sons Ltd.

Read more
April 21, 2020

A High-Quality Grapevine Downy Mildew Genome Assembly Reveals Rapidly Evolving and Lineage-Specific Putative Host Adaptation Genes.

Downy mildews are obligate biotrophic oomycete pathogens that cause devastating plant diseases on economically important crops. Plasmopara viticola is the causal agent of grapevine downy mildew, a major disease in vineyards worldwide. We sequenced the genome of Pl. viticola with PacBio long reads and obtained a new 92.94?Mb assembly with high contiguity (359 scaffolds for a N50 of 706.5?kb) due to a better resolution of repeat regions. This assembly presented a high level of gene completeness, recovering 1,592 genes encoding secreted proteins involved in plant-pathogen interactions. Plasmopara viticola had a two-speed genome architecture, with secreted protein-encoding genes preferentially located in gene-sparse, repeat-rich regions and evolving rapidly, as indicated by pairwise dN/dS values. We also used short reads to assemble the genome of Plasmopara muralis, a closely related species infecting grape ivy (Parthenocissus tricuspidata). The lineage-specific proteins identified by comparative genomics analysis included a large proportion of RxLR cytoplasmic effectors and, more generally, genes with high dN/dS values. We identified 270 candidate genes under positive selection, including several genes encoding transporters and components of the RNA machinery potentially involved in host specialization. Finally, the Pl. viticola genome assembly generated here will allow the development of robust population genomics approaches for investigating the mechanisms involved in adaptation to biotic and abiotic selective pressures in this species. © The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

Read more
April 21, 2020

Complete Genome Sequence of Actinosynnema pretiosum X47, An Industrial Strain that Produces the Antibiotic Ansamitocin AP-3.

Ansamitocins are extraordinarily potent antitumor agents. Ansamitocin P-3 (AP-3), which is produced by Actinosynnema pretiosum, has been developed as a cytotoxic drug for breast cancer. Despite its importance, AP-3 is of limited applicability because of the low production yield. A. pretiosum strain X47 was developed from A. pretiosum ATCC 31565 by mutation breeding and shows a relatively high AP-3 yield. Here, we analyzed the A. pretiosum X47 genome, which is ~8.13 Mb in length with 6693 coding sequences, 58 tRNA genes, and 15 rRNA genes. The DNA sequence of the ansamitocin biosynthetic gene cluster is highly similar to that of the corresponding cluster in A. pretiosum ATCC 31565, with 99.9% identity. However, RT-qPCR analysis showed that the expression levels of ansamitocin biosynthetic genes were significantly increased in X47 compared with the levels in the wild-type strain, consistent with the higher yield of AP-3 in X47. The annotated complete genome sequence of this strain will facilitate understanding the molecular mechanisms of ansamitocin biosynthesis and regulation in A. pretiosum and help further genetic engineering studies to enhance the production of AP-3.

Read more

Subscribe for blog updates:

Talk with an expert

If you have a question, need to check the status of an order, or are interested in purchasing an instrument, we're here to help.