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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
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Two epigenetic phenomena occur in crosses of Paramecium tetraurelia strains 32 and 51. Strain 32 is deficient for an IES present in one of the mating type genes, mtB, of strain 51. Internal eliminated sequences are excised from the developing macro-nuclear genome by a fascinating mechanism of genomic subtraction mediated by scanRNAs. However, if an IES is present in genome of one partner but absent in genome of another, then F1 hybrids deriving from the latter parent are unable to excise such IES from developing somatic genome: they can't produce a certain scanRNA. Moreover, F2 progeny of such cell will inherit this IES retained in macronucleus. IES inside a gene disrupts its function, thus reminding hybrid dysgenesis known for Drosophila. Indeed, in 25% of crosses we observed loss of mtB function in F2 progeny derived from parent 32. We also found unexpectedly that in 20% of crosses IES in mtB gene was retained in macronucleus of F2 progeny derived from parent 51, which normally produces scanRNAs and excises this IES. Analogous phenomenon was reported in cross of d12 and d48 deletion mutants of P. tetraurelia restoring functional gene of surface antigen A. We suggest that its mechanism may be connected with hemizygocity state ofthe deleted locus in F1 hybrids of such crosses, leading somehow to deviation of such sequence excision despite scanRNAs for it are present. These epigenetic effects may contribute into speciation in ciliates, as occasional hemizygocity may lead to lethality of interstrain hybrids. Supported by RFBR 16-04-01710.
RECONSTRUCTION OF CELLULAR SHAPE DEFORMATION THROUGH CONTRACTION OF CORTEX ACTOMYOSIN Nishigami Yukinori1, Ito Hiroaki2, Sonobe Seiji3, Ichikawa Masatoshi1
1 - Department of Physics, Graduate School ofScience, Kyoto University, Kyoto 606-8502, Japan
2 - Department ofMechanical Engineering, Graduate School ofEngineering, Osaka University, Osaka 5650871, Japan
3 - Department of Life Science, Graduate School of Life Science, University of Hyogo, Harima Science Park City, Hyogo 678-1297, Japan [email protected]
Giant free-living amoebae, Amoeba proteus, actively deform cellular shape during the locomotion. The deformation is induced by contraction of cortical actin and myosin (actomyosin). In the process, since actomyosin is connected to the cellar membrane and transmit the generated force to deform the membrane. Although the contractile properties of
actomyosin networks have been reported, actual contributions to the membrane deformation are still unclear because of the cellular complexities. Here, in order to simplify the complex system, we attempted to reconstitute a simple model system, in which lipid monolayer was deformed by actomyosin. In living cells, the connection between actomyosin and lipid layer is achieved by various types of proteins. To simply accomplish the actin-membrane connection in vitro, we adapted positively-charged lipid DOTAP (1,2-dioleoyl-3-trimethylammonium-propane), expecting the electrostatic adhesion between negatively-charged actin and DOTAP. We extracted actomyosin from A. proteus and enclosed actomyosin fraction within a spherical space surrounded by a DOTAP monolayer. As a result, active deformation ofthe lipid monolayer was yielded. From analyses ofthe static and dynamic properties of the deformation, we found that the depth and width ofthe deformation were dependent on the curvature radius of the sphere. The observed curvature dependence is explained by the theoretical description including elasticity and contractility of the cortex. Our results provide a fundamental insight into the cellular membrane deformation induced by the actomyosin cortex during amoeboid locomotion. For more details, see Nishigami et al. (Sci. Rep. 6, 19864, 2016) and Ito, Nishigami et al. (Phys. Rev. E92,062711,2015).
NUCLEAR DIVISION PROCESS IN TESTATE AMOEBA PAULINELLA CHROMATOPHORA Nomura M., Ishida K.
Faculty ofLife and Environmental Sciences, University of Tsukuba
Paulinella chromatophora is a euglyphid testate amoeba (Rhizaria, Cercozoa) living in a shell composed of ~50 rectangular siliceous scales. In this species, the complex shell construction process appears to be integrated under the cell cycle regulation, since the cell division does not proceed without the completion of shell construction. Before cell division, scales produced inside of mother cell are secreted out from the cell and assembled into a new shell by a specialized thick pseudopodium. Following the completion of shell construction, one of daughter cells moves into the new shell. Despite that knowledge, it is still unknown how the cell division process proceeds in response to the shell construction. In this study, we focused on how the nucleus divides along with shell construction process in P. chromatophora. In an intermediate stage of shell construction, the nucleus in the maternal cell was in prophase. In this phase, the nucleolus, which
