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52 • "PROTIST—2016
group. The branching pattern within the phaeoda-rian clade did not correspond to the families and the orders of the current classification system, and the system needs to be reconsidered.
CYANOBACTERIAL GENES IN THE NUCLEAR GENOME OF A DIATOM BEARING N2-FIXING CYANOBACTERIAL ENDOSYM-BIONTS: POTENTIAL FACTORS INVOLVED IN THE HOST-ENDOSYMBIONT PARTNERSHIP
Nakayama T., Inagaki Y.
Center for Computational Sciences, University of Tsukuba
The evolution of mitochondria and plastids from bacterial endosymbionts were key events in the evolution of eukaryotes. While the ancient nature of these organelles preclude understanding the transition from a bacterium to an organelle (organel-logenesis), the study of eukaryotic cells with recently evolved obligate endosymbiotic bacteria has the potential to provide important insights into the early events in the organellogenesis. Diatoms belonging to the family Rhopalodiaceae and their N2-fixing cyanobacterial endosymbionts (spheroid bodies) are emerging as a useful model system in this regard. The experimental data accumulated to date suggest that the endosymbiont has been already integrated into the host cell during the endosymbiotic relationship. Our previous study on the genome sequence of the endosymbiont in a rhopalodiacean diatom provided insight into its reductive evolution and the metabolic dependency on the diatom host. However, it has yet to be elucidated how the host control the endosymbionts. In this study, to tackle this question, we obtained both genome and transcriptomic data of a rhopalodiacean diatom, Epithemia adnata, as well as the genome data of its cyanobacterial endosymbiont. Phylogenetic analyses showed that the nuclear genome encodes protein-coding genes of cyanobacterial origin, which are not seen in other diatom genomes. Some of these 'cyanobacterial genes' likely encode enzymes involved in the metabolism ofpeptidoglycan wall, which is a feature exclusively associated with the endosymbiont in the E. adnata cell. We will overview the cyanobacterial genes found in the diatom genome, and discuss their possible contributions to the host-endosymbiont partnership.
PHYLOGENOMIC INSIGHTS ON THE EVOLUTION OF METCHNIKOVELLIDS Nassonova E.1-2, Moreira D.3, Torruella G.3, Timpano H.3, Paskerova G.2, Smirnov A.2, Lopez-
Garcia P.3
1 - Institute ofCytology RAS, St. Petersburg, Russia
2 - Department of Invertebrate Zoology, Faculty of Biology, St. Petersburg State University, St. Petersburg, Russia
3 - Unité d'Ecologie, Systématique et Evolution, CNRS, Université Paris-Sud, 91400 Orsay, France [email protected]
Metchnikovellids constitute a group of hyperpara-sites that infect gregarines living in the gut of polychaetes and other marine invertebrates. Despite they were described in the late 19th century, they are poorly known and their phylogenetic affinities have remained elusive for a long time. Morphological studies suggested an evolutionary relationship with Microsporidia, a group of highly derived intracellular parasites known for its extreme metabolic and genomic simplification, including e.g. loss of the mitochondrion. Microsporidia together with Rozellida (Cryptomycota) and Aphelida form a monophyletic holomycotan clade, the superphylum Opisthosporidia. The first molecular phylogenetic analyses based on SSU rRNA and beta-tubulin genes of Metchnikovella incurvata, a parasite of the gregarine Polyrhabdina sp. from the gut of the polychaete Pygospio elegans, supported a close evolutionary relationship with microsporidia. However, unraveling the phylogenetic position of these organisms is difficult due to their high evolutionary rate. To improve the phylogenetic signal and ascertain the phylogenetic position of metchnikovellids, we applied a single-cell genomics approach to individual gregarine cells infected with M. incurvata. We generated genome data by multiple displacement amplification followed by direct HiSeq 2500 Illumina sequencing. After assembly, we mined the genome dataset in search of conserved genes. Preliminary phylogenomic analyses of 31 conserved genes confirm the phylogenetic placement of metchnikovellids at the base of Microsporidia and after the divergence of Mitosporidium daphniae, a microsporidia-like mitochondrion-bearing parasite. Further exploration of metchnikovellid genomes would allow determining the genes and traits involved in the evolution of extreme parasitism. Supported by RFBR15-04-08870 and ERC 322669.
EPIGENETIC INCOMPATIBILITY OF PARA-MECIUM TETRAURELIA STRAINS Nekrasova I.1, Potekhin A.1, Kvitko J.1, Pellerin G.2, Meyer E.2
1 - Faculty of Biology, St Petersburg State University, Saint Petersburg, Russia
2 - Institut de Biologie, Ecole Normale Superieure, Paris, France
