Published Papers - Tanaka Atsuko

Vegetation variety affected by local environments in a coral reef lagoon

Kandai Tozaki, Gregory N. Nishihara, Azusa Kawate, Teruko Konishi, Yoichi Sato, Michihiro Ito, Hiroyuki Fujimura, Atsuko Tanaka

Phycological Research ( Wiley )    2024.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Abstract From shore to sea, coral reefs can generally be divided into a lagoon zone, a reef crest, and a fore reef. Environmental variables, such as nutrient fluxes, light availability, and water temperature, vary among the zones and influence the biodiversity of submerged macrophytes. Additionally, the biodiversity of vegetation within the lagoon appears to be affected by multiple and extremely localized conditions. We investigated the impact of small‐scale variations on vegetation diversity, and implemented an ecological survey within a well‐defined area inside of a lagoon at Bise Point, Okinawa, Japan. A total of 20 macroalgal species (four green algae, six brown algae, and ten red algae) and four seagrass species were identified from the surveyed quadrats over a period of 19 months, from October 2019 to March 2021. Patterns in species occurrence were spatially and temporally heterogeneous. Notably, water motion and sediment flux were highly variable among the monitoring sites. Redundancy analysis allowed us to evaluate the significance of environmental factors on the vegetation of each monitoring area. Six environmental factors were considered in this study, but their impacts on local vegetation were not equivalent. Redundancy analysis suggested that water depth, flow velocity, and the ratio of the small fraction of deposition particles were the three factors with the strongest influence on local vegetation. This study provides some crucial insights into the determinants of vegetation in a coral reef lagoon. Our findings suggest that the factors we examined exert more influence on the vegetation than seasonal effects.

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The Cell Wall Characterization of Brown Alga Cladosiphon okamuranus during Growth

Yuka Miwa, Mahanama Geegana, Gamage Awanthi, Kouichi Soga, Atsuko Tanaka, Michihiro Ito, Yuichiro Numata, Yoichi Sato, Teruko Konishi

Plants   12 ( 3274 )   2023.09 [ Peer Review Accepted ]

Type of publication: Research paper (other science council materials etc.)

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Characterization of cell wall polysaccharide from <scp><i>Cladosiphon okamuranus</i></scp> cultivated in different locations

Mahanama Geegana Gamage Awanthi, Natsuki Nakasone, Hirosuke Oku, Kanefumi Kitahara, Michihiro Ito, Atsuko Tanaka, Yoichi Sato, Yuichiro Numata, Teruko Konishi

Phycological Research ( Wiley )    2023.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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SUMMARY Cladosiphon okamuranus is an excellent source of fucoidan among any brown algae spp. However, the structure of polysaccharide varies significantly depending on the species, harvesting season and geographical location. To understand how geographic location affects the structure of cell wall polysaccharide, C. okamuranus cultivated in eight places (Bise, Katsuren, Yonashiro, Shikiya, Karimata, Nishihara, Hisamatsu and Ishigaki) in Ryukyu archipelago were collected during the peak harvesting time and the cell wall polysaccharide was analyzed physiochemically. The cell wall was sequentially fractionated into five fractions and its 80% was consisted of hot water fraction (HW) (60–70%) and hemicellulose‐I fraction (HC‐I) (15–20%), which mainly contained fucoidan composed of fucose (Fuc), glucuronic acid (GlcA) and sulfate (SO₃⁻). Although the chemical composition and molecular weight of fucoidan in HW was slightly different at different places, the composition of Fuc, GlcA and SO₃⁻ was constant in the molar ratio of 1.0:0.5:0.7–1.0 respectively, suggesting that relatively similar structural fucoidan from C. okamuranus can be obtained from any geographical location in Okinawa Prefecture during peak time. However, considerable variation in the sugar composition in HC‐I was observed, despite the uniform molecular weight and SO₃⁻. Particularly, HC‐I from Bise, where is the northern part of Okinawa Island, is composed of significantly higher amounts of Glc, Gal, Man, Xyl and morphologically thicker lateral branches compared to algae from the other parts of the island.

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Localization and characterization θ carbonic anhydrases in Thalassiosira pseudonana

Hermanus Nawaly, Atsuko Tanaka, Yui Toyoshima, Yoshinori Tsuji, Yusuke Matsuda

Photosynthesis Research ( Springer Science and Business Media LLC )    2023.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Pleiotropic Functions of Nitric Oxide Produced by Ascorbate for the Prevention and Mitigation of COVID-19: A Revaluation of Pauling's Vitamin C Therapy

Hideo Yamasaki, Hideyuki Imai, Atsuko Tanaka, Joji M. Otaki

Microorganisms ( MDPI AG )  11 ( 2 ) 397 - 397   2023.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Linus Pauling, who was awarded the Nobel Prize in Chemistry, suggested that a high dose of vitamin C (l-ascorbic acid) might work as a prevention or treatment for the common cold. Vitamin C therapy was tested in clinical trials, but clear evidence was not found at that time. Although Pauling's proposal has been strongly criticized for a long time, vitamin C therapy has continued to be tested as a treatment for a variety of diseases, including coronavirus infectious disease 2019 (COVID-19). The pathogen of COVID-19, SARS-CoV-2, belongs to the β-coronavirus lineage, which includes human coronavirus, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS). This review intends to shed new light on vitamin C antiviral activity that may prevent SARS-CoV-2 infection through the chemical production of nitric oxide (NO). NO is a gaseous free radical that is largely produced by the enzyme NO synthase (NOS) in cells. NO produced by upper epidermal cells contributes to the inactivation of viruses and bacteria contained in air or aerosols. In addition to enzymatic production, NO can be generated by the chemical reduction of inorganic nitrite (NO2−), an alternative mechanism for NO production in living organisms. Dietary vitamin C, largely contained in fruits and vegetables, can reduce the nitrite in saliva to produce NO in the oral cavity when chewing foods. In the stomach, salivary nitrite can also be reduced to NO by vitamin C secreted from the epidermal cells of the stomach. The strong acidic pH of gastric juice facilitates the chemical reduction of salivary nitrite to produce NO. Vitamin C contributes in multiple ways to the host innate immune system as a first-line defense mechanism against pathogens. Highlighting chemical NO production by vitamin C, we suggest that controversies on the therapeutic effects of vitamin C in previous clinical trials may partly be due to less appreciation of the pleiotropic functions of vitamin C as a universal bioreductant.

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Fractionation and characterization of cell wall polysaccharides from the brown alga Cladosiphon okamuranus

Mahanama Geegana Gamage Awanthi, Manatsu Umosa, Yoshiaki Yuguchi, Hirosuke Oku, Kanefumi Kitahara, Michihiro Ito, Atsuko Tanaka, Teruko Konishi

Carbohydrate Research ( Elsevier BV )  523   108722 - 108722   2023.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Nutrient uptake characteristics of Cladosiphon okamuranus (Phaeophyceae) from the Ryukyu Islands of Japan

Yoichi Sato, Eri Inomata, Hikari Nagoe, Michihiro Ito, Teruko Konishi, Hiroyuki Fujimura, Atsuko Tanaka, Gregory N. Nishihara

Journal of Applied Phycology ( Springer Science and Business Media LLC )  35 ( 1 ) 265 - 275   2022.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Variability in the Net Ecosystem Productivity (NEP) of Seaweed Farms

Yoichi Sato, Gregory N. Nishihara, Atsuko Tanaka, Dominic F, C. Belleza, Azusa Kawate, Yukio Inoue, Kenjiro Hinode, Yuhei Matsuda, Shinichiro Tanimae, Kandai Tozaki, Ryuta Terada, Hikaru Endo

Frontiers in Marine Science ( Frontiers Media SA )  9   2022.05 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The important role of vegetated ecosystems in the sequestration of carbon has gained strong interest across a wide variety of disciplines. With evidence growing of the potential for macroalgae ecosystems to capture carbon, there is burgeoning interest in applying newfound knowledge of carbon capture rates to better understand the potential for carbon sequestration. Seaweed farms are expected to play a significant role in carbon capture; advocates for the expansion of seaweed farms are increasing in many countries. In general, seaweed farms are expected to be highly productive, although whether they are autotrophic or heterotrophic ecosystems and hence potential exporters of carbon, is under debate. Therefore, we present our investigation of three seaweed farms, two in northern Japan and one in southern Japan. We examine the frequency of autotrophic days and compare potential rates of carbon capture of the seaweed farms with two natural macroalgae ecosystems and one degraded site. We estimated potential carbon capture rates by calculating the net ecosystem productivity from continuous recordings of dissolved oxygen concentrations under natural environmental conditions. The net ecosystem production rates for the natural ecosystems in Arikawa Bay and Omura Bay were equivalent to 0.043 and 0.054 [g C m^-2 d^-1] m^-1, respectively. Whereas, for the degraded ecosystem in Tainoura Bay, it was -0.01 [g C m^-2 d^-1] m^-1. We reveal that the Undaria pinnatifida farm in Matsushima Bay experience autotrophy more often than natural ecosystems, although for seaweed farms producing U. pinnatifida in Hirota Bay and Cladospihon okamuranus at Bise Point, autotrophy was less frequently observed. Nevertheless, up to 14.1 g C m^-2 (0.110 g C m^-2 d^-1) was captured by the production of U. pinnatifida and 3.6 g C m^-2 (0.034 g C m^-2 d^-1) was captured by C. okamuranus, and the total yield of carbon captured during 2021 production season for these farms was 43,385 kg C.

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Systematics, distribution, and sexual compatibility of six Scytosiphon species (Scytosiphonaceae, Phaeophyceae) from Japan and the description of four new species

Masakazu Hoshino, Atsuko Tanaka, Mitsunobu Kamiya, Shinya Uwai, Masanori Hiraoka, Kazuhiro Kogame

Journal of Phycology ( Wiley )  57 ( 2 ) 416 - 434   2021.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The brown alga Scytosiphon lomentaria (Scytosiphonaceae, Ectocarpales) has been reported from cold and warm waters worldwide. Although previous molecular phylogenetic studies and crossing experiments have shown that it is a complex of multiple distinct species, the taxonomic position and accurate distribution of each species have remained largely unclear. For the S. lomentaria complex from Japan, our cox1 and rbcL phylogenetic analyses detected six species. In addition to five previously detected species (species Ia-Va), one species (species VI) was newly found in the subtropical area, Okinawa Island. Species VI was recovered as a sister to species Ia-Va in rbcL. Based on the morphological and phylogenetic data, we concluded that species Ia is S. lomentaria, species IIIa is S. promiscuus, and the other four species are newly described: S. shibazakiorum for species IIa, S. tosaensis for species IVa, S. arcanus for species Va, and S. subtropicus for species VI. The cox1-based analysis also showed that S. lomentaria, S. shibazakiorum, and S. promiscuus have worldwide distributions, while the other three species were not found outside of Japan. In Japan, except for S. subtropicus, distributions of these species overlapped. Our crossing experiments showed that gametic incompatibility (pre-zygotic barrier) was less developed between the allopatric species (i.e., S. subtropicus and others) compared with the sympatric species. It may suggest that pre-zygotic barriers have evolved among the sympatric species due to reinforcement.

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Final yield of the brown alga Cladosiphon okamuranus ( Chordariaceae, Phaeophyceae ) may depend on nursery quality

Yoichi Sato, Hikari Nagoe, Michihiro Ito, Teruko Konishi, Hiroyuki Fujimura, Gregory N. Nishihara, Atsuko Tanaka

Phycological Research ( Wiley )  69 ( 3 ) 159 - 165   2021.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Cladosiphon okamuranus (Chordariaceae, Phaeophyceae) production is an important economic activity in the islands of Okinawa, Japan, and has been unstable for the past decade. Local producers surmise that unstable yields are related to highly localized environmental conditions. We report that the differential yields of C. okamuranus harvested from experimental nets during the 2019 season at two adjacent nurseries (less than 40 m apart), which were designated as a poor or good nursery by local producers, were 137 and 253 kg (wet weight), respectively. In fact, nutrient conditions between the poor and good nursery were slightly different, although involvement of some unsurveyed environmental factors cannot be excluded at present. Additionally, we report on a thallus shearing phenomenon that led to the catastrophic loss of thalli from the cultivation nets.

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Community-Level Responses to Iron Availability in Open Ocean Plankton Ecosystems

Luigi Caputi, Quentin Carradec, Damien Eveillard, Amos Kirilovsky, Eric Pelletier, Juan J. Pierella Karlusich, Fabio Rocha Jimenez Vieira, Emilie Villar, Samuel Chaffron, Shruti Malviya, Eleonora Scalco, Silvia G. Acinas, Adriana Alberti, Jean-Marc Aury, Anne-Sophie Benoiston, Alexis Bertrand, Tristan Biard, Lucie Bittner, Martine Boccara, Jennifer R. Brum, Christophe Brunet, Greta Busseni, Anna Carratala, Herve Claustre, Luis Pedro Coelho, Sbastien Colin, Salvatore D'Aniello, Corinne Da Silva, Marianna Del Core, Hugo Dore, Stephane Gasparini, Florian Kokoszka, Jean-Louis Jamet, Christophe Lejeusne, Cyrille Lepoivre, Magali Lescot, Gipsi Lima-Mendez, Fabien Lombard, Julius Lukes, Nicolas Maillet, Mohammed-Amin Madoui, Elodie Martinez, Maria Grazia Mazzocchi, Mario B. Neou, Javier Paz-Yepes, Julie Poulain, Simon Ramondenc, Jean-Baptiste Romagnan, Simon Roux, Daniela Salvagio Manta, Remo Sanges, Sabrina Speich, Mario Sprovieri, Shinichi Sunagawa, Vincent Taillandier, Atsuko Tanaka, Leila Tirichine, Camille Trottier, Julia Uitz, Alaguraj Veluchamy, Jana Vesela, Flora Vincent, Sheree Yau, Stefanie Kandels-Lewis, Sarah Searson, Cline Dimier, Marc Picheral, Peer Bork, Emmanuel Boss, Colomban De Vargas, Michael J. Follows, Nigel Grimsley, Lionel Guidi, Pascal Hingamp, Eric Karsenti, Paolo Sordino, Lars Stemmann, Matthew B. Sullivan, Alessandro Tagliabue, Adriana Zingone, Laurence Garczarek, Fabrizio d'Ortenzio, Pierre Testor, Fabrice Not, Maurizio Ribera d'Alcala, Patrick Wincker, Chris Bowler, Daniele Iudicone, Gabriel Gorsky, Olivier Jaillon, Lee Karp-Boss, Uros Krzic, Hiroyuki Ogata, Stephane Pesant, Jeroen Raes, Emmanuel G. Reynaud, Christian Sardet, Mike Sieracki, Didier Velayoudon, Jean Weissenbach

GLOBAL BIOGEOCHEMICAL CYCLES ( AMER GEOPHYSICAL UNION )  33 ( 3 ) 391 - 419   2019.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Predicting responses of plankton to variations in essential nutrients is hampered by limited in situ measurements, a poor understanding of community composition, and the lack of reference gene catalogs for key taxa. Iron is a key driver of plankton dynamics and, therefore, of global biogeochemical cycles and climate. To assess the impact of iron availability on plankton communities, we explored the comprehensive bio-oceanographic and bio-omics data sets from Tara Oceans in the context of the iron products from two state-of-the-art global scale biogeochemical models. We obtained novel information about adaptation and acclimation toward iron in a range of phytoplankton, including picocyanobacteria and diatoms, and identified whole subcommunities covarying with iron. Many of the observed global patterns were recapitulated in the Marquesas archipelago, where frequent plankton blooms are believed to be caused by natural iron fertilization, although they are not captured in large-scale biogeochemical models. This work provides a proof of concept that integrative analyses, spanning from genes to ecosystems and viruses to zooplankton, can disentangle the complexity of plankton communities and can lead to more accurate formulations of resource bioavailability in biogeochemical models, thus improving our understanding of plankton resilience in a changing environment.Plain Language Summary Marine phytoplankton require iron for their growth and proliferation. According to John Martin's iron hypothesis, fertilizing the ocean with iron could dramatically increase photosynthetic activity, thus representing a biological means to counteract global warming. However, while there is a constantly growing knowledge of how iron is distributed in the ocean and about its role in cellular processes in marine photosynthetic groups such as diatoms and cyanobacteria, less is known about how iron availability shapes plankton communities and how they respond to it. In the present work, we exploited recently published Tara Oceans data sets to address these questions. We first defined specific subcommunities of co-occurring organisms that co-vary with iron availability in the oceans. We then identified specific patterns of adaptation and acclimation to iron in different groups of phytoplankton. Finally, we validated our global results at local scale, specifically in the Marquesas archipelago, where recurrent phytoplankton blooms arc believed to be a result of iron fertilization. By integrating global data with a localized response, we provide a framework for understanding the resilience of plankton ecosystems in a changing environment.

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Asexual reproduction of the marine green alga Struvea okamurae

Yusuke Horinouchi, Akihiro Dozono, Atsuko Tanaka, Tatsuya Togashi

Marine Biosystems Research   33   2 - 7   2019

Type of publication: Research paper (other science council materials etc.)

Theme session “Marine science researches of Okinawa Research Core for Highly Innovative Discipline Science (ORCHIDS) project"

Takashi NAKAMURA, James Davis REIMER, Ryuichi SHINJO, Mamoru NAKAMURA, Atsuko TANAKA, Hin Boo WEE

Journal of the Japanese Coral Reef Society ( Japanese Coral Reef Society )  21 ( 1 ) 1 - 12   2019 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Branch regeneration induced by sever damage in the brown alga Dictyota dichotoma (dictyotales, phaeophyceae).

Tanaka A, Hoshino Y, Nagasato C, Motomura T

Protoplasma ( Protoplasma )  254 ( 3 ) 1341 - 1351   2017.05 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Tissue wounds are mainly caused by herbivory, which is a serious threat for macro-algae, and brown algae are known to regenerate branches or buds in response to wounding. In the present paper, we describe a branch regeneration system, induced by sever damage, in the brown alga Dictyota dichotoma. Segmentations of juvenile thalli induced branch regenerations unless explants possessed apical cells. Apical excisions in distinct positions elucidated that disruption of an apical cell or disconnection of tissue with an apical cell triggered the branch regeneration. Furthermore, spatial positions of regenerated branches seemed to be regulated by the apical region, which was assumed to generate inhibitory effects for lateral branch regeneration. Mechanical incision, which disrupted tissue continuity with the apical region, induced branch regeneration preferentially below the incision. Although we were unable to identify the candidate inhibitory substance, our results suggested that the apical region may have an inhibitory effect on lateral branch regeneration. Additionally, observations of branch regeneration showed that all epidermal cells in D. dichotoma possess the ability to differentiate into apical cells, directly. This may be the first report of algal transdifferentiation during the wound-stress response.

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Intercellular translocation of molecules via plasmodesmata in the multiseriate filamentous brown alga, Halopteris congesta (Sphacelariales, Phaeophyceae).

Nagasato C, Tanaka A, Ito T, Katsaros C, Motomura T

Journal of phycology ( Journal of Phycology )  53 ( 2 ) 333 - 341   2017.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Despite the high number of studies on the fine structure of brown algal cells, only limited information is available on the intercelluar transportation of molecules via plasmodesmata in brown algae. In this study, plasmodesmatal permeability of Halopteris congesta was examined by observing the translocation of microinjected fluorescent tracers of different molecular sizes. The tip region of H. congesta consists of a cylindrical apical cell, while the basal region is multiseriate. Fluorescein isothiocyanate-dextran (FD; 3, 10, and 20 kDa) and recombinant green fluorescent protein (27 kDa) were injected into the apical cell and were observed to diffuse into the neighboring cells. FD of 40 kDa was detected only in the injected apical cell. The plasmodesmatal size exclusion limit was considered to be more than 20 kDa and less than 40 kDa. The extent of translocation of 3 and 10 kDa FD from the apical to neighboring cells 2 h postinjection was estimated based on the fluorescence intensity. It was suggested that the diffusing capacity of plasmodesmata varied according to molecular size. In order to examine acropetal and/or basipetal direction of molecular movement, 3 and 10 kDa FD were injected into the third cell from the apical cell. Successive observations indicated that the diffusion of fluorescence in the acropetal direction took longer than that in the basipetal direction. No ultrastructural difference in plasmodesmata was noted among the cross walls.

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Chemotaxis in the anisogamous brown alga Mutimo cylindricus (Cutleriaceae, Tilopteridales)

Nana Kinoshita, Chikako Nagasato, Atsuko Tanaka, Taizo Motomura

PHYCOLOGIA ( INT PHYCOLOGICAL SOC )  55 ( 4 ) 359 - 364   2016 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Locomotion of female and male gametes of Mutimo cylindricus was analysed using a high-speed recording system. Female and male gametes morphologically differed in terms of their cell size and flagellar length. Male gametes swam significantly faster than female gametes; although, the flagellar waveforms were almost the same. Thus, the different swimming velocities of male and female gametes may have been due to differences in their cell size. Chemotactic male gametes treated with the sex pheromone from settled female gametes behaved in a similar manner to the male gametes of the isogamous Ectocarpus siliculosus. The results of the study revealed the following: (1) free-swimming male gametes exhibited thigmotaxis, (2) the beat frequency of the anterior flagellum and the swimming velocity decreased, (3) the deflection angle of the anterior flagellum increased, (4) the unilateral beat of the posterior flagellum was affected by the sex pheromone gradient, and (5) the tracking radius of male gametes around female gametes decreased.

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Ultrastructure and Membrane Traffic During Cell Division in the Marine Pennate Diatom Phaeodactylum tricornutum.

Tanaka A, De Martino A, Amato A, Montsant A, Mathieu B, Rostaing P, Tirichine L, Bowler C

Protist ( ELSEVIER GMBH, URBAN & FISCHER VERLAG )  166 ( 5 ) 506 - 21   2015.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The marine pennate diatom Phaeodactylum tricornutum has become a model for diatom biology, due to its ease of culture and accessibility to reverse genetics approaches. While several features underlying the molecular mechanisms of cell division have been described, morphological analyses are less advanced than they are in other diatoms. We therefore examined cell ultrastructure changes prior to and during cytokinesis. Following chloroplast division, cleavage furrows are formed at both longitudinal ends of the cell and are accompanied by significant vesicle transport. Although neither spindle nor microtubules were observed, the nucleus appeared to be split by the furrow after duplication of the Golgi apparatus. Finally, centripetal cytokinesis was completed by fusion of the furrows. Additionally, F-actin formed a ring structure and its diameter became smaller, accompanying the ingrowing furrows. To further analyse vesicular transport during cytokinesis, we generated transgenic cells expressing yellow fluorescent protein (YFP) fusions with putative diatom orthologs of small GTPase Sec4 and t-SNARE protein SyntaxinA. Time-lapse observations revealed that SyntaxinA-YFP localization expands from both cell tips toward the center, whereas Sec4-YFP was found in the Golgi and subsequently relocalizes to the future division plane. This work provides fundamental new information about cell replication processes in P. tricornutum. (C) 2015 The Authors. Published by Elsevier GmbH.

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Energetic coupling between plastids and mitochondria drives CO2 assimilation in diatoms.

Bailleul B, Berne N, Murik O, Petroutsos D, Prihoda J, Tanaka A, Villanova V, Bligny R, Flori S, Falconet D, Krieger-Liszkay A, Santabarbara S, Rappaport F, Joliot P, Tirichine L, Falkowski PG, Cardol P, Bowler C, Finazzi G

Nature ( NATURE PUBLISHING GROUP )  524 ( 7565 ) 366 - 9   2015.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Diatoms are one of the most ecologically successful classes of photosynthetic marine eukaryotes in the contemporary oceans. Over the past 30 million years, they have helped to moderate Earth's climate by absorbing carbon dioxide from the atmosphere, sequestering it via the biological carbon pump and ultimately burying organic carbon in the lithosphere(1). The proportion of planetary primary production by diatoms in the modern oceans is roughly equivalent to that of terrestrial rainforests(2). In photosynthesis, the efficient conversion of carbon dioxide into organic matter requires a tight control of the ATP/NADPHratio which, in other photosynthetic organisms, relies principally on a range of plastid-localized ATP generating processes(3-6). Here we show that diatoms regulate ATP/NADPH through extensive energetic exchanges between plastids and mitochondria. This interaction comprises the re-routing of reducing power generated in the plastid towards mitochondria and the import of mitochondrial ATP into the plastid, and is mandatory for optimized carbon fixation and growth. We propose that the process may have contributed to the ecological success of diatoms in the ocean.

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Development and function of plasmodesmata in zygotes of Fucus distichus

Chikako Nagasato, Makoto Terauchi, Atsuko Tanaka, Taizo Motomura

BOTANICA MARINA ( WALTER DE GRUYTER GMBH )  58 ( 3 ) 229 - 238   2015.06 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Brown algae have plasmodesmata, tiny tubular cytoplasmic channels connecting adjacent cells. The lumen of plasmodesmata is 10-20 nm wide, and it takes a simple form, without a desmotubule (the inner membrane structure consisting of endoplasmic reticulum in the plasmodesmata of green plants). In this study, we analyzed the ultrastructure and distribution of plasmodesmata during development of Fucus distichus zygotes. The first cytokinesis of zygotes in brown algae is not accompanied by plasmodesmata formation. As the germlings develop, plasmodesmata are found in all septal cell walls, including the first cell division plane. Plasmodesmata are formed de novo on the existing cell wall. Pit fields, which are clusters of plasmodesmata, were observed in germlings with differentiated cell layers. Apart from the normal plasmodesmata, these pit fields had branched plasmodesmata that appeared to arise from the lateral preexisting ones. Fluorescent tracers with different molecular sizes were microinjected to examine the size exclusion limit of molecules for transit through the plasmodesmata. Fluorescein isothiocyanate (FITC)-dextran of 3 kDa size was spread over the germlings, and 10 kDa FITC-dextran was tracked only in the rhizoid. The size exclusion limit was &lt;10 kDa for the thallus but &lt;40 kDa for the rhizoid.

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Ocean plankton. Environmental characteristics of Agulhas rings affect interocean plankton transport.

Villar E, Farrant GK, Follows M, Garczarek L, Speich S, Audic S, Bittner L, Blanke B, Brum JR, Brunet C, Casotti R, Chase A, Dolan JR, d'Ortenzio F, Gattuso JP, Grima N, Guidi L, Hill CN, Jahn O, Jamet JL, Le Goff H, Lepoivre C, Malviya S, Pelletier E, Romagnan JB, Roux S, Santini S, Scalco E, Schwenck SM, Tanaka A, Testor P, Vannier T, Vincent F, Zingone A, Dimier C, Picheral M, Searson S, Kandels-Lewis S, Tara Oceans Coordinators., Acinas SG, Bork P, Boss E, de Vargas C, Gorsky G, Ogata H, Pesant S, Sullivan MB, Sunagawa S, Wincker P, Karsenti E, Bowler C, Not F, Hingamp P, Iudicone D

Science (New York, N.Y.) ( AMER ASSOC ADVANCEMENT SCIENCE )  348 ( 6237 ) 1261447   2015.05 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Agulhas rings provide the principal route for ocean waters to circulate from the Indo-Pacific to the Atlantic basin. Their influence on global ocean circulation is well known, but their role in plankton transport is largely unexplored. We show that, although the coarse taxonomic structure of plankton communities is continuous across the Agulhas choke point, South Atlantic plankton diversity is altered compared with Indian Ocean source populations. Modeling and in situ sampling of a young Agulhas ring indicate that strong vertical mixing drives complex nitrogen cycling, shaping community metabolism and biogeochemical signatures as the ring and associated plankton transit westward. The peculiar local environment inside Agulhas rings may provide a selective mechanism contributing to the limited dispersal of Indian Ocean plankton populations into the Atlantic.

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Functional characterization of the diatom cyclin-dependent kinase A2 as a mitotic regulator reveals plant-like properties in a non-green lineage.

Huysman MJ, Tanaka A, Bowler C, Vyverman W, De Veylder L

BMC plant biology ( BIOMED CENTRAL LTD )  15   86   2015.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Background: Cyclin-dependent kinases (CDKs) are crucial regulators of cell cycle progression in eukaryotes. The diatom CDKA2 was originally assigned to the classical A-type CDKs, but its cell cycle phase-specific transcription at the G2-to-M phase transition is typical for plant-specific B-type CDKs. Results: Here, we report the functional characterization of CDKA2 from the diatom Phaeodactylum tricornutum. Through a yeast two-hybrid library screen, CDKA2 was found to interact with the G2/M-specific CDK scaffolding factor CKS1. Localization of CDKA2 was found to be nuclear in interphase cells, while in cells undergoing cytokinesis, the signal extended to the cell division plane. In addition, overexpression of CDKA2 induced an overall reduction in the cell growth rate. Expression analysis of cell cycle marker genes in the overexpression lines indicates that this growth reduction is primarily due to a prolongation of the mitotic phase. Conclusions: Our study indicates a role for CDKA2 during cell division in diatoms. The functional characterization of a CDK with clear CDKB properties in a non-green organism questions whether the current definition of B-type CDKs being plant-specific might need revision.

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A novel protein, ubiquitous in marine phytoplankton, concentrates iron at the cell surface and facilitates uptake.

Morrissey J, Sutak R, Paz-Yepes J, Tanaka A, Moustafa A, Veluchamy A, Thomas Y, Botebol H, Bouget FY, McQuaid JB, Tirichine L, Allen AE, Lesuisse E, Bowler C

Current biology : CB ( CELL PRESS )  25 ( 3 ) 364 - 71   2015.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Numerous cellular functions including respiration require iron. Plants and phytoplankton must also maintain the iron-rich photosynthetic electron transport chain, which most likely evolved in the iron-replete reducing environments of the Proterozoic ocean [1]. Iron bioavailability has drastically decreased in the contemporary ocean [1], most likely selecting for the evolution of efficient iron acquisition mechanisms among modern phytoplankton. Mesoscale iron fertilization experiments often result in blooms dominated by diatoms [2], indicating that diatoms have adaptations that allow survival in iron-limited waters and rapid multiplication when iron becomes available. Yet the genetic and molecular bases are unclear, as very few iron uptake genes have been functionally characterized from marine eukaryotic phytoplankton, and large portions of diatom iron starvation transcriptomes are genes encoding unknown functions [3-5]. Here we show that the marine diatom Phaeodactylum tricomutum utilizes ISIP2a to concentrate Fe(III) at the cell surface as part of a novel, copper-independent and thermodynamically controlled iron uptake system. ISIP2a is expressed in response to iron limitation several days prior to the induction of ferrireductase activity, and it facilitates significant Fe(III) uptake during the initial response to Fe limitation. ISIP2a is able to directly bind Fe(III) and increase iron uptake when heterologously expressed, whereas knockdown of ISIP2a in P. tricomutum decreases iron uptake, resulting in impaired growth and chlorosis during iron limitation. ISIP2a is expressed by diverse marine phytoplankton, indicating that it is an ecologically significant adaptation to the unique nutrient composition of marine environments.

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Phaeophysema gen. nov and Vimineoleathesia gen. nov., new brown algal genera for the minute Japanese members of the genus Leathesia

Tanaka Atsuko, Uwai Shinya, Nelson Wendy, Kawai Hiroshi

EUROPEAN JOURNAL OF PHYCOLOGY   45 ( 1 ) 107 - 115   2010 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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