A tutorial of diverse genome analysis tools found in the CoGe web-platform usingPlasmodiumspp. as a model

Expanding the Triangle of U: Comparative analysis of the Hirschfeldia incana genome provides insights into chromosomal evolution, phylogenomics and high photosynthesis-related traits

BACKGROUND AND AIMS

The Brassiceae tribe encompasses many economically important crops and exhibits high intraspecific and interspecific phenotypic variation. After a shared whole-genome triplication (WGT) event (Br-α, ~15.9 million years ago), differential lineage diversification and genomic changes contributed to an array of divergence in morphology, biochemistry, and physiology underlying photosynthesis-related traits. Here, the C3 species Hirschfeldia incana is studied as it displays high photosynthetic rates under high-light conditions. Our aim was to elucidate the evolution that gave rise to the genome of H. incana and its high-photosynthesis traits.

METHODS

We reconstructed a chromosome-level genome assembly for H. incana (Nijmegen, v2.0) using nanopore and chromosome conformation capture (Hi-C) technologies, with 409Mb in size and an N50 of 52Mb (a 10× improvement over the previously published scaffold-level v1.0 assembly). The updated assembly and annotation was subsequently employed to investigate the WGT history of H. incana in a comparative phylogenomic framework from the Brassiceae ancestral genomic blocks and related diploidized crops.

KEY RESULTS

Hirschfeldia incana (x=7) shares extensive genome collinearity with Raphanus sativus (x=9). These two species share some commonalities with Brassica rapa and B. oleracea (A genome, x=10 and C genome, x=9, respectively) and other similarities with B. nigra (B genome, x=8). Phylogenetic analysis revealed that H. incana and R. sativus form a monophyletic clade in between the Brassica A/C and B genomes. We postulate that H. incana and R. sativus genomes are results of hybridization or introgression of the Brassica A/C and B genome types. Our results might explain the discrepancy observed in published studies regarding phylogenetic placement of H. incana and R. sativus in relation to the "Triangle of U" species. Expression analysis of WGT retained gene copies revealed sub-genome expression divergence, likely due to neo- or sub-functionalization. Finally, we highlighted genes associated with physio-biochemical-anatomical adaptive changes observed in H. incana which likely facilitate its high-photosynthesis traits under high light.

CONCLUSIONS

The improved H. incana genome assembly, annotation and results presented in this work will be a valuable resource for future research to unravel the genetic basis of its ability to maintain a high photosynthetic efficiency in high-light conditions and thereby improve photosynthesis for enhanced agricultural production.

The NIH Comparative Genomics Resource: addressing the promises and challenges of comparative genomics on human health

Comparative genomics is the comparison of genetic information within and across organisms to understand the evolution, structure, and function of genes, proteins, and non-coding regions (Sivashankari and Shanmughavel, Bioinformation 1:376-8, 2007). Advances in sequencing technology and assembly algorithms have resulted in the ability to sequence large genomes and provided a wealth of data that are being used in comparative genomic analyses. Comparative analysis can be leveraged to systematically explore and evaluate the biological relationships and evolution between species, aid in understanding the structure and function of genes, and gain a better understanding of disease and potential drug targets. As our knowledge of genetics expands, comparative genomics can help identify emerging model organisms among a broader span of the tree of life, positively impacting human health. This impact includes, but is not limited to, zoonotic disease research, therapeutics development, microbiome research, xenotransplantation, oncology, and toxicology. Despite advancements in comparative genomics, new challenges have arisen around the quantity, quality assurance, annotation, and interoperability of genomic data and metadata. New tools and approaches are required to meet these challenges and fulfill the needs of researchers. This paper focuses on how the National Institutes of Health (NIH) Comparative Genomics Resource (CGR) can address both the opportunities for comparative genomics to further impact human health and confront an increasingly complex set of challenges facing researchers.

Discovery of novel virulence mechanisms in Clostridium botulinum type A3 using genome-wide analysis

OBJECTIVE

Clostridium botulinum type A is a neurotoxin-producing, spore-forming anaerobic bacterium that causes botulism in humans. The evolutionary genomic context of this organism is not yet known to understand its molecular virulence mechanisms in the human intestinal tract. Hence, this study aimed to investigate the mechanisms underlying virulence and pathogenesis by comparing the genomic contexts across species, serotypes, and subtypes.

METHODS

A comparative genomic approach was used to analyze evolutionary genomic relationships, intergenomic distances, syntenic blocks, replication origins, and gene abundance with phylogenomic neighbors.

RESULTS

Type A strains have shown genomic proximity to group I strains with distinct accessory genes and vary even within subtypes. Phylogenomic data showed that type C and D strains were distantly related to a group I and group II strains. Synthetic plots indicated that orthologous genes might have evolved from Clostridial ancestry to subtype A3 strains, whereas syntonic out-paralogs might have emerged between subtypes A3 and A1 through α-events. Gene abundance analysis revealed the key roles of genes involved in biofilm formation, cell-cell communication, human diseases, and drug resistance compared to the pathogenic Clostridia. Moreover, we identified 43 unique genes in the type A3 genome, of which 29 were involved in the pathophysiological processes and other genes contributed to amino acid metabolism. The C. botulinum type A3 genome contains 14 new virulence proteins that can provide the ability to confer antibiotic resistance, virulence exertion and adherence to host cells, the host immune system, and mobility of extrachromosomal genetic elements.

CONCLUSION

The results of our study provide insight into the understanding of new virulence mechanisms to discover new therapeutics for the treatment of human diseases caused by type A3 strains.

Navigating the CoGe Online Software Suite for Polyploidy Research

The CoGe software suite at genomevolution.org hosts a number of tools that facilitate genomic research on plant and animal whole-genome multiplication-polyploidy. SynMap permits analysis and visualization of two-way syntenic dotplot alignments of genomes, includes many options and data/graphics download possibilities, and even permits three-genome synteny maps and interactive views. FractBias is a tool that operates within SynMap that permits calculation and graphic display of genome fragments (such as chromosomes) of one species mapped to another, displaying both blockwise homology depths and the extent of syntenic gene (syntelog) loss following polyploidy events. SynMap macrosynteny results can segue into the microsynteny tool GEvo, which provides genome-browser-like views of homologous genome blocks. CoGe FeatView allows call-up of given gene features already stored in the CoGe resource, and CoGeBlast permits searches for additional features that can be analyzed or downloaded further. Links from these tools can be fed into SynFind, which can find syntenic blocks surrounding a feature across multiple specified genomes while also simultaneously providing overall genome-wide syntenic depth calculations that can be interpreted to reflect polyploidy levels. Here, we describe basic use of these tools on the CoGe software suite.

Tracking of Diversity and Evolution in the Brown Rot Fungi Monilinia fructicola, Monilinia fructigena, and Monilinia laxa

Monilinia species are among the most devastating fungi worldwide as they cause brown rot and blossom blight on fruit trees. To understand the molecular bases of their pathogenic lifestyles, we compared the newly assembled genomes of single strains of Monilinia fructicola, M. fructigena and M. laxa, with those of Botrytis cinerea and Sclerotinia sclerotiorum, as the closest species within Sclerotiniaceae. Phylogenomic analysis of orthologous proteins and syntenic investigation suggest that M. laxa is closer to M. fructigena than M. fructicola, and is closest to the other investigated Sclerotiniaceae species. This indicates that M. laxa was the earliest result of the speciation process. Distinct evolutionary profiles were observed for transposable elements (TEs). M. fructicola and M. laxa showed older bursts of TE insertions, which were affected (mainly in M. fructicola) by repeat-induced point (RIP) mutation gene silencing mechanisms. These suggested frequent occurrence of the sexual process in M. fructicola. More recent TE expansion linked with low RIP action was observed in M. fructigena, with very little in S. sclerotiorum and B. cinerea. The detection of active non-syntenic TEs is indicative of horizontal gene transfer and has resulted in alterations in specific gene functions. Analysis of candidate effectors, biosynthetic gene clusters for secondary metabolites and carbohydrate-active enzymes, indicated that Monilinia genus has multiple virulence mechanisms to infect host plants, including toxins, cell-death elicitor, putative virulence factors and cell-wall-degrading enzymes. Some species-specific pathogenic factors might explain differences in terms of host plant and organ preferences between M. fructigena and the other two Monilinia species.

Comparative genomic analysis of hyper-ammonia producing Acetoanaerobium sticklandii DSM 519 with purinolytic Gottschalkia acidurici 9a and pathogenic Peptoclostridium difficile 630

Acetoanaerobium sticklandii DSM519 (CST) is a hype-ammonia producing non-pathogenic anaerobe that can use amino acids as important carbon and energy sources through the Stickland reactions. Biochemical aspects of this organism have been extensively studied, but systematic studies addressing its metabolic discrepancy remain scant. In this perspective, we have intensively analyzed its genomic and metabolic characteristics to comprehend the evolutionary conservation of amino acid catabolism by a comparative genomic approach. The whole-genome data indicated that CST has shown a phylogenomic similarity with hyper-ammonia producing, purinolytic, and proteolytic pathogenic Clostridia. CST has shown to common genomic context sharing across the purinolytic Gottschalkia acidurici 9a and pathogenic Peptoclostridium difficile 630. Genome syntenic analysis described that syntenic orthologs might be originated from the recent ancestor at a slow evolution rate and syntenic-out paralogs evolved from either CDF or CAC via α-event and β-event. Collinearity of either gene orders or gene families was adjusted with syntenic out-paralogs across these genomes. The genome-wide metabolic analysis predicted 11 unique putative metabolic subsystems from the CST genome for amino acid catabolism and hydrogen production. The in silico analysis of our study revealed that a characteristic system for amino acid catabolism-directed biofuel synthesis might have slowly evolved and established as a core genomic content of CST.

The genetic basis of water-use efficiency and yield in lettuce

BACKGROUND

Water supply limits agricultural productivity of many crops including lettuce. Identifying cultivars within crop species that can maintain productivity with reduced water supply is a significant challenge, but central to developing resilient crops for future water-limited climates. We investigated traits known to be related to water-use efficiency (WUE) and yield in lettuce, a globally important leafy salad crop, in a recombinant inbred line (RIL) lettuce mapping population, produced from a cross between the cultivated Lactuca sativa L. cv. Salinas and its wild progenitor L. serriola L.

RESULTS

Wild and cultivated lettuce differed in their WUE and we observed transgressive segregation in yield and water-use traits in the RILs. Quantitative trait loci (QTL) analysis identified genomic regions controlling these traits under well-watered and droughted conditions. QTL were detected for carbon isotope discrimination, transpiration, stomatal conductance, leaf temperature and yield, controlling 4-23 % of the phenotypic variation. A QTL hotspot was identified on chromosome 8 that controlled carbon isotope discrimination, stomatal conductance and yield under drought. Several promising candidate genes in this region were associated with WUE, including aquaporins, late embryogenesis abundant proteins, an abscisic acid-responsive element binding protein and glutathione S-transferases involved in redox homeostasis following drought stress were also identified.

CONCLUSIONS

For the first time, we have characterised the genetic basis of WUE of lettuce, a commercially important and water demanding crop. We have identified promising candidate genomic regions determining WUE and yield under well-watered and water-limiting conditions, providing important pre-breeding data for future lettuce selection and breeding where water productivity will be a key target.

Elsinoë australis Causing Spot Anthracnose on Poplar in China

Poplar plantations provide important industrial feedstock in China. Red spot symptoms were observed on leaves of Populus tomentosa and P. deltoides in southeastern China. Based on morphology and molecular phylogenetic analysis, the fungus isolated from disease spots was identified as Elsinoë australis, which has been previously recognized as a pathogen of Citrus spp. and jojoba but has not been reported in China. Pathogenicity tests found that isolates from two poplar species caused red spot symptoms on leaves from different poplar species and also led to scab formation on the fruit of one hybrid citrus but not on fruit of orange, lemon, or grapefruit. The draft genome of one E. australis isolate was generated. The genetic architecture of the MAT1-1 and MAT1-2 loci of E. australis was revealed by genome sequence and long-range PCR analyses. Single isolates carried only one of two opposite mating-types was confirmed by idiomorph-specific PCR, suggesting a heterothallic mating system. Our results not only revealed a new E. australis pathotype causing poplar spot anthracnose in China but also provided its genome and mating system information.

Transcriptomic and evolutionary analysis of the mechanisms by which P. argentatum, a rubber producing perennial, responds to drought

BACKGROUND

Guayule (Parthenium argentatum Gray) is a drought tolerant, rubber producing perennial shrub native to northern Mexico and the US Southwest. Hevea brasiliensis, currently the world's only source of natural rubber, is grown as a monoculture, leaving it vulnerable to both biotic and abiotic stressors. Isolation of rubber from guayule occurs by mechanical harvesting of the entire plant. It has been reported that environmental conditions leading up to harvest have a profound impact on rubber yield. The link between rubber biosynthesis and drought, a common environmental condition in guayule's native habitat, is currently unclear.

RESULTS

We took a transcriptomic and comparative genomic approach to determine how drought impacts rubber biosynthesis in guayule. We compared transcriptional profiles of stem tissue, the location of guayule rubber biosynthesis, collected from field-grown plants subjected to water-deficit (drought) and well-watered (control) conditions. Plants subjected to the imposed drought conditions displayed an increase in production of transcripts associated with defense responses and water homeostasis, and a decrease in transcripts associated with rubber biosynthesis. An evolutionary and comparative analysis of stress-response transcripts suggests that more anciently duplicated transcripts shared among the Asteraceae, rather than recently derived duplicates, are contributing to the drought response observed in guayule. In addition, we identified several deeply conserved long non-coding RNAs (lncRNAs) containing microRNA binding motifs. One lncRNA in particular, with origins at the base of Asteraceae, may be regulating the vegetative to reproductive transition observed in water-stressed guayule by acting as a miRNA sponge for miR166.

CONCLUSIONS

These data represent the first genomic analyses of how guayule responds to drought like conditions in agricultural production settings. We identified an inverse relationship between stress-responsive transcripts and those associated with precursor pathways to rubber biosynthesis suggesting a physiological trade-off between maintaining homeostasis and plant productivity. We also identify a number of regulators of abiotic responses, including transcription factors and lncRNAs, that are strong candidates for future projects aimed at modulating rubber biosynthesis under water-limiting conditions common to guayules' native production environment.

Gene duplication and evolution in recurring polyploidization-diploidization cycles in plants

BACKGROUND

The sharp increase of plant genome and transcriptome data provide valuable resources to investigate evolutionary consequences of gene duplication in a range of taxa, and unravel common principles underlying duplicate gene retention.

RESULTS

We survey 141 sequenced plant genomes to elucidate consequences of gene and genome duplication, processes central to the evolution of biodiversity. We develop a pipeline named DupGen_finder to identify different modes of gene duplication in plants. Genes derived from whole-genome, tandem, proximal, transposed, or dispersed duplication differ in abundance, selection pressure, expression divergence, and gene conversion rate among genomes. The number of WGD-derived duplicate genes decreases exponentially with increasing age of duplication events-transposed duplication- and dispersed duplication-derived genes declined in parallel. In contrast, the frequency of tandem and proximal duplications showed no significant decrease over time, providing a continuous supply of variants available for adaptation to continuously changing environments. Moreover, tandem and proximal duplicates experienced stronger selective pressure than genes formed by other modes and evolved toward biased functional roles involved in plant self-defense. The rate of gene conversion among WGD-derived gene pairs declined over time, peaking shortly after polyploidization. To provide a platform for accessing duplicated gene pairs in different plants, we constructed the Plant Duplicate Gene Database.

CONCLUSIONS

We identify a comprehensive landscape of different modes of gene duplication across the plant kingdom by comparing 141 genomes, which provides a solid foundation for further investigation of the dynamic evolution of duplicate genes.

Tail Wags the Dog? Functional Gene Classes Driving Genome-Wide GC Content in Plasmodium spp

Plasmodium parasites are valuable models to understand how nucleotide composition affects mutation, diversification, and adaptation. No other observed eukaryotes have undergone such large changes in genomic Guanine-Cytosine (GC) content as seen in the genus Plasmodium (∼30% within 35-40 Myr). Although mutational biases are known to influence GC content in the human-infective Plasmodium vivax and Plasmodium falciparum; no study has addressed how different gene functional classes contribute to genus-wide compositional changes, or if Plasmodium GC content variation is driven by natural selection. Here, we tested the hypothesis that certain gene processes and functions drive variation in global GC content between Plasmodium species. We performed a large-scale comparative genomic analysis using the genomes and predicted genes of 17 Plasmodium species encompassing a wide genomic GC content range. Genic GC content was sorted and divided into ten equally sized quantiles that were then assessed for functional enrichment classes. In agreement that selection on gene classes may drive genomic GC content, trans-membrane proteins were enriched within extreme GC content quantiles (Q1 and Q10). Specifically, variant surface antigens, which primarily interact with vertebrate immune systems, showed skewed GC content distributions compared with other trans-membrane proteins. Although a definitive causation linking GC content, expression, and positive selection within variant surface antigens from Plasmodium vivax, Plasmodium berghei, and Plasmodium falciparum could not be established, we found that regardless of genomic nucleotide composition, genic GC content and expression were positively correlated during trophozoite stages. Overall, these data suggest that, alongside mutational biases, functional protein classes drive Plasmodium GC content change.