74 research outputs found
Reconstructing the phylogenetic relationships of nematodes using draft genomes and transcriptomes
No full textNematoda is a very diverse animal phylum. Within Nematoda, species display a
multitude of life styles, different reproductive strategies and parasitism has arisen
independently several times. Furthermore, morphological conservation and a high
rate of homoplasy have impeded the resolution of nematode systematics. To address
these issues, single gene (usually the nuclear ribosomal small subunit gene) and
mitochondrial gene phylogenies have been used, but the information contained within
the sequence of these genes is not enough to resolve the topological relationships
between clades that emerged during rapid cladogenesis.
Next generation sequencing data have been shown to produce high quality genomic
and transcriptomic assemblies at low cost, as a result more and more nematode
species are being sequenced. Sequences were gathered or generated for 53 nematode
species from ESTs, gene predictions from full genome assemblies and transcripts
from RNA-Seq experiments. These sequences were screened for orthologous gene
clusters, which were concatenated into a supermatrix with thousands of aminoacid
sites. The analysis of the supermatrix with maximum likelihood and Bayesian inference
methods sheds light into the early splitting clades of the phylogenetic tree
of nematodes and the derived clades III, IV and V. Furthermore, the phylogenetic
relationships within the parastitic family Onchocercidae were resolved, unveiling the
evolutionary history of these important taxa. Finally, data produced in this work
will be useful for subsequent evolutionary studies of the phylum Nematoda
DNA transposons drive genome evolution of the root-knot nematode Meloidogyne incognita
No full textA recommendation – based on reviews by Daniel Vitales and two anonymous reviewers – of the article: Kozlowski DK, Hassanaly-Goulamhoussen R, Da-Rocha M, Koutsovoulos G, Bailly-Bechet M, Danchin EG (2020) Transposable Elements are an evolutionary force shaping genomic plasticity in the parthenogenetic root-knot nematode Meloidogyne incognita. bioRxiv, 2020.04.30.069948, ver. 4 peer-reviewed and recommended by PCI Evolutionary Biology. https://doi.org/10.1101/2020.04.30.06994
The scandalous pest
No full textA recommendation – based on reviews by two anonymous reviewers – of the article: Koutsovoulos, G. D., Marques, E., Arguel, M. J., Duret, L., Machado, A. C. Z., Carneiro, R. M. D. G., Kozlowski, D. K., Bailly-Bechet, M., Castagnone-Sereno, P., Albuquerque, E. V., and Danchin, E. G. J.(2019). Population genomics supports clonal reproduction and multiple gains and losses of parasitic abilities in the most devastating nematode plant pest. bioRxiv, 362129, ver. 5, peer-reviewed and recommended by Peer Community in Evolunary Biology. doi: 10.1101/36212
Phylogenomics and analysis of shared genes suggest a single transition to mutualism in Wolbachia of nematodes
No full textWolbachia, endosymbiotic bacteria of the order Rickettsiales, are widespread in arthropods but also present in nematodes. In arthropods, A and B supergroup Wolbachia are generally associated with distortion of host reproduction. In filarial nematodes, including some human parasites, multiple lines of experimental evidence indicate that C and D supergroup Wolbachia are essential for the survival of the host, and here the symbiotic relationship is considered mutualistic. The origin of this mutualistic endosymbiosis is of interest for both basic and applied reasons: How does a parasite become a mutualist? Could intervention in the mutualism aid in treatment of human disease? Correct rooting and high-quality resolution of Wolbachia relationships are required to resolve this question. However, because of the large genetic distance between Wolbachia and the nearest outgroups, and the limited number of genomes so far available for large-scale analyses, current phylogenies do not provide robust answers. We therefore sequenced the genome of the D supergroup Wolbachia endosymbiont of Litomosoides sigmodontis, revisited the selection of loci for phylogenomic analyses, and performed a phylogenomic analysis including available complete genomes (from isolates in supergroups A, B, C, and D). Using 90 orthologous genes with reliable phylogenetic signals, we obtained a robust phylogenetic reconstruction, including a highly supported root to the Wolbachia phylogeny between a (A + B) clade and a (C + D) clade. Although we currently lack data from several Wolbachia supergroups, notably F, our analysis supports a model wherein the putatively mutualist endosymbiotic relationship between Wolbachia and nematodes originated from a single transition event
Toward 959 nematode genomes
No full textThe sequencing of the complete genome of the nematode Caenorhabditis elegans was a landmark achievement and ushered in a new era of whole-organism, systems analyses of the biology of this powerful model organism. The success of the C. elegans genome sequencing project also inspired communities working on other organisms to approach genome sequencing of their species. The phylum Nematoda is rich and diverse and of interest to a wide range of research fields from basic biology through ecology and parasitic disease. For all these communities, it is now clear that access to genome scale data will be key to advancing understanding, and in the case of parasites, developing new ways to control or cure diseases. The advent of second-generation sequencing technologies, improvements in computing algorithms and infrastructure and growth in bioinformatics and genomics literacy is making the addition of genome sequencing to the research goals of any nematode research program a less daunting prospect. To inspire, promote and coordinate genomic sequencing across the diversity of the phylum, we have launched a community wiki and the 959 Nematode Genomes initiative (www.nematodegenomes.org/). Just as the deciphering of the developmental lineage of the 959 cells of the adult hermaphrodite C. elegans was the gateway to broad advances in biomedical science, we hope that a nematode phylogeny with (at least) 959 sequenced species will underpin further advances in understanding the origins of parasitism, the dynamics of genomic change and the adaptations that have made Nematoda one of the most successful animal phyla
The genome of Romanomermis culicivorax:revealing fundamental changes in the core developmental genetic toolkit in Nematoda
No full textThe genetics of development in the nematode Caenorhabditis elegans has been described in exquisitedetail. The phylum Nematoda has two classes: Chromadorea (which includes C. elegans) and theEnoplea. While the development of many chromadorean species resembles closely that of C. elegans,enoplean nematodes show markedly different patterns of early cell division and cell fate assignment.Embryogenesis of the enoplean Romanomermis culicivorax has been studied in detail, but the geneticcircuitry underpinning development in this species has not been explored
AvP: A software package for automatic phylogenetic detection of candidate horizontal gene transfers.
No full textHorizontal gene transfer (HGT) is the transfer of genes between species outside the transmission from parent to offspring. Due to their impact on the genome and biology of various species, HGTs have gained broader attention, but high-throughput methods to robustly identify them are lacking. One rapid method to identify HGT candidates is to calculate the difference in similarity between the most similar gene in closely related species and the most similar gene in distantly related species. Although metrics on similarity associated with taxonomic information can rapidly detect putative HGTs, these methods are hampered by false positives that are difficult to track. Furthermore, they do not inform on the evolutionary trajectory and events such as duplications. Hence, phylogenetic analysis is necessary to confirm HGT candidates and provide a more comprehensive view of their origin and evolutionary history. However, phylogenetic reconstruction requires several time-consuming manual steps to retrieve the homologous sequences, produce a multiple alignment, construct the phylogeny and analyze the topology to assess whether it supports the HGT hypothesis. Here, we present AvP which automatically performs all these steps and detects candidate HGTs within a phylogenetic framework
Recent Advances in Population Genomics of Plant-Parasitic Nematodes
No full textInternational audiencePlant-parasitic nematodes are a costly burden of crop production. Ubiquitous in nature, phytoparasitic nematodes are associated with nearly every important agricultural crop and represent a significant constraint on global food security. Population genetics is a key discipline in plant nematology to understand aspects of the life strategies of these parasites, in particular their modes of reproduction, geographic origins, evolutionary histories, and dispersion abilities. Advances in high-throughput sequencing technologies have enabled a recent but active effort in genomic analyses of plant-parasitic nematodes. Such genomic approaches applied to multiple populations are providing new insights into the molecular and evolutionary processes that underpin the establishment of these nematodes and into a better understanding of the genetic and mechanistic basis of their pathogenicity and adaptation to their host plants. In this review, we attempt to update information about genome resources and genotyping techniques useful for nematologists who are thinking about initiating population genomics or genome sequencing projects. This review is intended also to foster the development of population genomics in plant-parasitic nematodes through highlighting recent publications that illustrate the potential for this approach to identify novel molecular markers or genes of interest and improve our knowledge of the genome variability, pathogenicity, and evolutionary potential of plant-parasitic nematodes
Ancient and novel small RNA pathways compensate for the loss of piRNAs in multiple independent nematode lineages
No full textDate of Acceptance: 02/01/2015Small RNA pathways act at the front line of defence against transposable elements across the Eukaryota. In animals, Piwi interacting small RNAs (piRNAs) are a crucial arm of this defence. However, the evolutionary relationships among piRNAs and other small RNA pathways targeting transposable elements are poorly resolved. To address this question we sequenced small RNAs from multiple, diverse nematode species, producing the first phylum-wide analysis of how small RNA pathways evolve. Surprisingly, despite their prominence in Caenorhabditis elegans and closely related nematodes, piRNAs are absent in all other nematode lineages. We found that there are at least two evolutionarily distinct mechanisms that compensate for the absence of piRNAs, both involving RNA-dependent RNA polymerases (RdRPs). Whilst one pathway is unique to nematodes, the second involves Dicer-dependent RNA-directed DNA methylation, hitherto unknown in animals, and bears striking similarity to transposon-control mechanisms in fungi and plants. Our results highlight the rapid, context-dependent evolution of small RNA pathways and suggest piRNAs in animals may have replaced an ancient eukaryotic RNA-dependent RNA polymerase pathway to control transposable elements.Peer reviewe
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