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We propose a subject for a thesis iin the team Parasites and Free-living Protists at the Muséum national d'Histoire naturelle (Paris) concerning the Contribution of marine gregarines to the evolutionary history of Apicomplexa and adaptation to parasitic lifestyle
The funding of the thesis will depend on the competition at the dosctoral school of the Muséum (ED227).
Apicomplexa, unicellular eukaryotes representing ~6,000 species, have all adopted a strict parasitic lifestyle . They include intracellular parasites of vertebrates developing in one to several hosts, responsible for serious pathologies: malaria, toxoplasmosis, cryptosporidiosis. Their genomes have been sequenced and serve as references for comparative genomics and the reconstruction of evolutionary history of Apicomplexa. However, these parasites of vertebrate represent only the tip of the iceberg, since Apicomplexa also include gregarines, parasites of a wide variety of non-vertebrate hosts (polychaetes, crustaceans, insects, etc.) representing ~40% of Apicomplexa biodiversity [1,2]. They are mainly extracellular, monoxenous and non-pathogenic, and are poorly known at genomic level, due to the current impossibility to cultivate them. They are mainly extracellular, monoxenous and considered non-pathogenic.
Recently, two photo-autotrophic proto-Apicomplexa associated with corals, Vitrella and Chromera, have been sequenced. The comparative analysis of their genomes with data on Plasmodium, Toxoplasma and Cryptosporidium has revealed groups of genes/functions lost (mainly) and acquired during the transition to the intracellular parasitic lifestyle [3-5]. However, the vision of this transition remains incomplete in the absence of data on gregarines, phylogenetically placed at the base of the apicomplexan speciation, among which archigregarines are considered as having diverged the earliest .
The PPL laboratory has been involved since 2017 in the -omic analysis (genome, transcriptome) of marine (Porospora gigantea) and terrestrial (Gregarina acridiorum) intestinal eugregarines, in close collaboration with the Bioinformatics Support Unit of the AVIV Department (Evelyne Duvernois-Berthet and Dr. Loic Ponger) and in the framework of Julie Boisard's PhD thesis (ED227, CNRS funding, 2018-2021). This work has made it possible to develop efficient procedures for the genesis and analysis of these original –omic data, despite the intrinsic methodological and analytical difficulties.
Within the framework of this project, we wish to consolidate our expertise by complementing the approach with two new marine grearine biological models, which are more difficult to study biologically but which are likely to provide different elements of speciation due to their phylogeny or biology: the intestinal archigregarine Selenidium pendula and the coelomic eugregarine Diplauxis hatti .
The study of these two species will include: genome and transcriptome sequencing, genome assembly and gene prediction, and expert data mining. This will allow a comparative analysis with the terrestrial and marine intestinal eugregarines currently studied in the laboratory, in order to better explore the specific traits of this group. It will provide a better understanding of the evolutionary scenarii that have accompanied the establishment of parasitism in Apicomplexa and the progressive conquest of vertebrate hosts, towards polyxenous parasitism and intracellular lifestyle.
Several specific tasks will be addressed:
1- Inventory of the protein heritage deduced from genome analysis, exploration of the molecular architecture of key apicomplexan structures/functions (apical complex, IMC (inner membrane complex), mitochondria, apicoplast, motility) and assessment of the maintenance of metabolic pathways with reference to other (proto)-Apicomplexa and outgroups.
2- Research and reconstruction of potential mitochondrial and apicoplast genomes from genomic data.
3- Identification of genes/functions gains and losses compared to documented occurrences in proto-Apicomplexa and other apicomplexans; establishment of evolutionary scenariii.
4- Phylogenetic studies of preserved components.
The abundant literature available for Plasmodium, Toxoplasma, Cryptosporidium, as well as the genomic and post-genomic data available, will serve as references for digging up these new gregarines data; comparative studies will be based on recent work with Vitrella and Chromera [3-5] and emerging works on few gregarines [6-7].
The analyses will be mainly carried out bioinformatically. Depending on the results obtained, experiments may be implemented for: 1) experimental validation of certain gene models by RT-PCR/Sanger sequencing, 2) confirmation of the presence of a mitochondrion and/or an apicoplast (transmission electron microscopy).
1. Portman N, Slapeta J. Trends Parasitol, 2014. 30(2): p. 58-64.
2. Desportes I, Schrevel L. Brill, editor, 2013.
3. Janouskovec J et al., PNAS, 2015. 112(33): p. 10200-7.
4. Templeton TJ, Pain A. Parasitology, 2016, 143(1): p. 1-17.
5. Woo YH et al., Elife, 2015, 4: p. e06974.
6. Janouskovec J. et al., eLife, 2019, 8.
7. Mathur, V., et al., Current biology, 2019, 29:2936-2941 e293