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Protistology ■ 51
najdrova.vladimira@seznam.cz Giardia intestinalis, an anaerobic protozoan parasite, contains highly compact genome with extremely short untranslated regions (UTRs). The regulation ofgene expression during giardia cell- and life-cycle has been poorly studied and only a handful of RNA binding proteins have been characterized so far. PUF proteins bind 3' UTRs of cognate mRNAs, by which they regulate their stability, translation and localization. These eukaryotic proteins are evolutionarily conserved from protists to metazoans. We have identified five PUF genes in the genome of G. intestinalis and have initiated studies towards the characterization of PUFs in giardia biology.
EXPLORING CELL TYPE DIFFERENTIATION IN THE FILASTEREAN CAPSASPORA OWCZARZAKI BY SINGLE-CELL RNA-SEQ Najle S.R.1, Florenza J.1, Mazutis L.2, Ruiz-Trillo
I 1,3,4
1 - Institut de Biologia Evolutiva (Univesitat Pompeu Fabra — CSIC). Pg. Maritim de la Barceloneta 37-49, 08003, Barcelona, Catalonia, Spain
2 - Institute ofBiotechnology, Vilnius University. V.A. Graiciuno 8, LT-02241, Vilnius, Lithuania
3 - Departament de Genutica, Universitat de Barcelona, Av. Diagonal, 645, Barcelona 08028, Catalonia, Spain
4 - Instituciy Catalana de Recerca i Estudis Avangats (ICREA), Passeig Lluis Companys, 23, Barcelona 08010, Catalonia, Spain. sebastian.najle@upf.edu
The origin of multicellular animals from their unicellular ancestors is one of the most important evolutionary transitions in life's history. However, the specific cellular and genetic changes that led to this transition remain unknown. Phylogenomic analyses have shown that animals are closely related to three unicellular lineages: choanoflagellates, filastereans and ichthyosporeans, altogether forming the Holozoa clade. Recent phylogenomic studies have shown that those premetazoan taxa already had a complex repertoire of genes important for multicellularity, some of them previously thought to be exclusive of animals. Different versions of "simple multicellularity" are found among the unicellular relatives of Metazoa. There is the clonal development of colonial choanoflagellates, the aggregative behavior of Capsaspora owczarzaki, and the coenocytic development of ichthyosporeans. Those colonies and aggregates are assumed to be without cell differentiation. However, there is no molecular data proving that all cells within those colonies or aggregates or coenocytes are identical. Here we show microscopic evidence for the coexis-
tence of different cell types in C. owczarzaki aggregates. We also show our advances in developing single-cell transcriptomics methodology in these organism to molecularly characterize cell types. The possibility of analyzing differential gene expression at the single-cell level between diverse cell types of unicellular holozoans will allow us to better understand the molecular mechanisms underlying programs of cell differentiation in the origin of animals. The aggregates of C. owczarzaki offer us an ideal model in which to test this, and provide a better framework to understand the origin of the different metazoan cell types.
PHYLOGENY AND ECOLOGICAL IMPORTANCE OF PHAEODARIANS (CERCOZOA, RHIZARIA)
Nakamura Y.1, Somiya R.2, Suzuki N.3, Hori S. R.4, Tuji A.1
1 - Department ofBotany, National Museum ofNature and Science
2 - Graduate School of Fisheries Science and Environmental Studies, Nagasaki University
3 - Graduate School ofScience, Tohoku University
4 - Graduate School ofScience and Engineering, Ehime University
y.nakamura@fish.hokudai.ac.jp Phaeodarians are a group of marine protists belonging to the phylum Cercozoa, composing Rhizaria (SAR). These unicellular siliceous zooplankton occasionally become abundant in the ocean, however their ecological importance and phylogeny are still wrapped in mystery. Plankton were sampled from several depths at ca. 40 stations in the Northern hemisphere during 2011—2015. Zooplankton were sorted and identified in order to clarify the species composition of each sample. Some phaeodarians were cultured to observe their behavior. The 18S rDNA sequences of phaeodarians were determined by single-cell PCR method. Two undescribed phaeodarians were found in the deep waters in the Sea of Japan, and one of the species was abundant through the year, occupying ca. 22% of the total zooplankton biomass on average. The abundance of phaeodarians was also seen in the East China Sea, where two species occupied 10.2—13.9% of the zooplankton biomass, suggesting that this group is an important component of the zooplankton community and the material cycle in the ocean. The cell division ofphaeodarians was observed during the culture experiment. The species morphologically identified as phaeodarians formed a single clade together with other cercozoans in the phylogenetic tree, suggesting that almost all phaeodarians belong to Cercozoa and that Phaeodaria is a monophyletic
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
ntakuro@ccs.tsukuba.ac.jp
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 puri.lopez.@u-psud.fr
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
