Contribution of marine gregarines to the evolutionary history of Apicomplexa and adaptation to parasitic lifestyle
Thesis Director: HDR Pr FLORENT Isabelle (Isabelle.firstname.lastname@example.org) and Co-director: Dr PONGER Loïc, (email@example.com)
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 vertebrates 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.
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 .
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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.
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