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Abstracts of Oral Presentations
The abstracts are split into the five sections in which they were presented, click on the headings below to jump to each section.
Section 1: (Comparative) algal genomics
Section 2: Ectocarpus genomics
Section 3: Biochemistry & physiology
Section 4: Developmental biology
Section 5: Biodiversity & evolution
Session 1: (Comparative) algal genomics
Chair: D Schroeder
Kroth PG, Weber T & Gruber A
Diatom metabolism
Diatoms are important primary producers in all aquatic habitats. Together with brown algae they belong to the heterokont algae, which have evolved by secondary endocytobiosis. This process included the uptake of an ancestor of modern red algae by a eukaryotic host cell, followed by a transformation of the endosymbiont into an organelle. As a consequence various secondary gene transfers occurred from the vanishing nucleus of the endosymbiont to the nucleus of the host cell. Recent sequencing of the genomes of the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana indeed revealed that both eukaryotic cells (host and endosymbiont) left their imprint in the diatom genome and that metabolic pathways have been rearranged within the diatoms. Here we report on the unusual distribution of enzymes of the carbohydrate pathways and the light regulation of photosynthesis in diatoms.
Department of Biology, University of Konstanz, 78457, Konstanz, Germany
Gruber A, Vugrinec S & Kroth P
Protein targeting into secondary plastids of diatoms
Plastids of heterokonts (including diatoms and brown algae), and related algae evolved by secondary endocytobiosis, the uptake of a eukaryotic alga into a eukaryotic host cell and its subsequent evolutionary reduction into an organelle. As a result, these "complex" plastids are surrounded by four membranes. In diatoms, protein targeting of nucleus encoded plastid proteins across these membranes depends on N-terminal bipartite presequences consisting of a signal and a transit peptide-like domain. A conserved amino acid motif of unknown function at the cleavage site of the signal peptides ("ASAFAP") is particularly important for plastid targeting. We characterised the requirements for stromal presequences by screening of genomic databases and by fusion of different presequence domains to Green Fluorescent Protein. Metabolites also have to cross the four plastid membranes, thus metabolite transporters are crucial for the function of the plastid. Membrane transporters identified in diatom genomes differ in their presequence structure: they possess either (i) a full bipartite presequence including an "ASAFAP"-motif, or (ii) the bipartite presequence lacks the conserved motif, or (iii) no presequence is recognisable. Multiple copies of metabolite transporter genes might therefore explain the multiple membrane transport of metabolites.
Department of Biology, University of Konstanz, 78457, Konstanz, Germany
Gschlößl B(1),(2), Guermeur Y(3) & Cock JM(1),(2)
HECTAR: A method which allows the prediction of N-terminal subcellular targeting for whole proteomes of the heterokonts
Subcellular targeting in heterokont has been shown to be more complex than in many other eukaryotic organisms. This is due to the secondary endosymbiosis event that occurred in an ancestor of this group, in which a red algae was taken up into a eukaryotic heterotroph and transformed in a chloroplast with four surrounding membranes. As a consequence, many chloroplast targeted proteins in heterokonts possess N-terminal bipeptide target peptides which consist of a leading signal peptide followed by a chloroplast transit peptide. Actual available prediction methods are unable to efficiently identify this targeting sequence. We have developed HECTAR (Heterokont subCellular TARgeting), a prediction method which is adapted to the specific subcellular addressing system in heterokonts. The method has been designed to predict one of five categories of N-terminal subcellular targeting to a protein sequence: Signal peptides, type II signal anchors, chloroplast transit peptides, mitochondrion transit peptides and proteins which do not posses any N-terminal target peptide. We have used a hierarchical concept consisting of three modules to decipher the target peptides of heterokonts. In a each of the modules we have combined established subcellular prediction methods for a specific target peptide by a Support Vector Machine. HECTAR achieves high performances in detecting the specific subcellular localisations. We also show that this prediction method is capable of assigning subcellular localisations to entire proteomes.
(1) UPMC Univ Paris 6, UMR 7139 Vegetaux marins et Biomolecules, Station Biologique, F 29682, Rosco, France
(2) CNRS, UMR 7139 Vegetaux marins et Biomolecules, Station Biologique, F 29682, Rosco, France
(3) LORIA-CNRS, Campus Scientique, BP 239, 54506 Vanduvre-les-Nancy cedex, France
Corresponding author: J Mark Cock cock@sb-roscoff.fr
Session 2: Ectocarpus genomics
Chair: A Peters
Cock JM(1), Peters AF(1), Coelho S(1), Scornet D(1), Charrier B(1), Gschlößl B(1), Ratin M(1), Cho GY(1), Heesch S(1), Farnham G(1), Remblière C(1), Dittami S(1), Tonon T(1), Samanta M(2), Sterck L(3), Rouzé P(3), van de Peer Y(3), Weissenbach J(4) & Wincker P(4)
The Ectocarpus genome project
A survey of several brown algal species led to the proposition of Ectocarpus siliculosus as a potential genetic and genomic model for this group of organisms (Peters et al., J. Phycol. 2004). A genome sequencing project for this organism was initiated at Genoscope in 2004. This project involved the generation of about three and a half million sequencing reads from genomic libraries with various sized inserts, plus an additional 91,000 cDNA reads. A draft assembly of the 200 Mbp genome was completed in the summer of 2007 and a prediction of the protein coding genes in the genome was then made at the VIB in Ghent using the automatic annotation program Eugene. An international consortium of annotators is currently annotating the genome manually, based on the results of the automatic annotation. The presentation will describe some of the major steps of this project and some of the complementary projects that are being carried out, including a tiling array hybridisation experiment and the construction of a genetic map. A summary of some of the initial results of the manual annotation will also be presented.
(1)Station Biologique de Roscoff, UMR 7139 CNRS-UPMC, Marine Plants and Biomolecules, Place Georges Teissier, BP74, 29682 Roscoff Cedex, France
(2)Systemics Institute, CA, USA
(3)VIB / University of Gent, Bioinformatics & Evolutionary Genomics, Technologiepark 927, B-9052 Gent, Belgium
(4)Genoscope, 2 rue Gaston Crémieux, CP5706, 91057 Evry cedex, France
Charrier B, Le Bail A, Dittami S, Maisonneuve C, Gicquel M, de Franco P-O, Rousvoal S, Cock JM & Tonon T
Additional Ectocarpus post-genomic tools: a mini-library of mutants and identification of normalisation genes for expression analyses
We present two types of tools, which have been developed in the frame of our study in Ectocarpus. First, a mini-library of 60 mutants displaying alterations in their developmental pattern has been produced. Some of them show a modified resistance to osmotic stresses, or are impaired in their competence for adhesion. The cellular and molecular characterisation of several of these mutants has been initiated. Modifications of the cell types and the overall organisation of the filaments were observed, correlating with the organisation of the cytoskeleton (a-tubulin immunolocalisation) and the expression of related-genes (Q-PCR). Secondly, 13 housekeeping genes that can be used to normalise gene expression have been selected from the genomic resources (ribosomal protein 26S, EF1alpha, IF2A, IF4E, ubiquitin, ubiquitin conjugating enzyme, cyclophilin, tubulin alpha, actin, actin-related proteins, dynein, glucose 6-phosphate dehydrogenase). The stability of their expression level was assessed by Q-PCR in samples representing 20 different culture conditions, using different methods of calculation (Ct range, geNorm and Normfinder). The results showed that EF1-alpha was the best gene for normalisation, and excluded actin as a good reference, both results being in agreement with previous studies in other organisms.
Station Biologique de Roscoff, Place Georges Tessier, Roscoff, 29682, France
(author for correspondence: B Charrier)
Schroeder DC
A genomic approach to profile the Ectocarpus virus lysogenic transcriptome
Viruses are the most abundant biological agents in the sea. While several lytic viruses infecting prokaryotic and eukaryotic microalgae have been well characterised, little is known about the biology of lysogenic viruses that infect macroalgae. The only group of lysogenic viruses studied in any detail are the ectocarpoid phaeoviruses. This study applied genomic technologies to build a framework and knowledge base to understand the lysogenic nature of the ectocarpoid virus infection cycle. DNA microarray based transcriptomic data will be presented highlighting fascinating expression patterns.
Marine Biological Association, Citadel Hill, Plymouth, PL1 2PB, UK
Dittami S, Scornet D, Cock M, Boyen C & Tonon T
Transcriptomic study of abiotic stress response in Ectocarpus siliculosus by oligonucleotide microarray
We have designed an oligonucleotide microarray comprising 17 000 unigenes from five different sporophyte/gametophyte EST libraries and the E. siliculosus virus genes. Each sequence is represented by four 60-meres probes. Targets (double strand cDNA) for the array were transcribed and amplified from mRNA (3)0ng) or total RNA (1)00ng) using the Clontech SMART cDNA synthesis kit. The production of the slides, labeling and hybridization were carried out by Nimblegen. We present the microarray as well as its first application for the study and comparison of transcriptomic changes in response to abiotic stress: hyper- and hyposaline conditions as well oxidative stress. This data is complemented by physiological measures such as photosynthesis and selected metabolites. In order to facilitate a global analysis of the gene expression data an automated annotation of the unigenes represented on the array with Gene Ontology and KEGG ontology terms was performed using GOPET and KOBAS programs. These annotations will be made available to the Ectocarpus community. The results of this pilot experiment will serve as a guideline for future Ectocarpus microarray experiments. The gene expression service is available for purchase through Nimblegen and represents a valuable tool for anybody interested in studying the transcriptome of E. siliculosus.
Station Biologique de Roscoff, Place Georges Tessier, Roscoff, 29682, France
Session 3: Biochemistry & physiology
Chair: D Müller
Pohnert G
The pheromone chemistry of brown algae
The overview will cover the research on brown algal pheromones from the first structural characterisation of an active principle in 1971 to the recent detailed insight into their biosynthesis. Special emphasis is placed on the inactivation of initially released pheromones through pericyclic reactions. The development of analytical methods and bioassays that lead to the identification of a structural variety of different fatty acid-derived pheromones is also discussed. It will be illustrated which impact pheromone-research on brown algae has on the elucidation of the defensive chemistry of brown algae and diatoms.
Friedrich-Schiller-Universität, Inst. für Anorganische und Analytische Chemie, Lessingstr. 8, D-07743, Jena, Germany
Rui F & Boland W
Mechanistic aspects of pheromone formation in Ectocarpus siliculosus
In Ectocarpus siliculosus, like in most of brown algae, female gametes attract their conspecifics with a volatile pheromone. During this process sexual cells transform certain fatty acids into hydrocarbons. From previous studies it is known that the chirality of the released substances plays a role in bioactivity in some brown algal species, and in general the composition varies from enantiomerically pure to well-defined enantiomeric mixtures. Ectocarpus siliculosus is a useful model system to study the enzymatic activity generating pheromones in brown algae. With this aim we examined the mechanism of pheromone formation by incubation of gametes with a fatty acid precursor deuterated in strategic positions and GC/MS analysis of volatiles. We report that the optical purity of the hydrocarbon in Ectocarpus siliculosus is extremely high and that the enzymatic basis of the enantiomeric excess is a stereospecific hydrogen removal, a mechanistic feature that reminds of enzymes processing polyunsaturated fatty acids like lipoxygenases. Moreover, after volatile emission the precursor fatty acid stored in cell lipids is depleted of an amount comparable with that of the emitted volatile. This means that gametes massively mobilize their reserve fatty acid into this signalling pathway.
Max Planck Institute for Chemical Ecology, Jena, 07745, Germany
Schmid D(1), Motomura T(2), Nagasato C(2) & Boland W(1)
Comparative proteome analysis of brown algal gametes
Sexual reproduction of brown algae (Phaeophyceae) is mediated by pheromones. To attract male gametes female gametes are producing volatile organic compounds such as ectocarpene which are released into the surrounding water. Male gametes perceive these pheromones and immediately direct their swimming to the female gametes. The initial step of mating is the recognition of the possible mating partner. This process is mediated by specific surface proteins. Therefore membrane proteins are supposed to play a major role in the mating process of brown algae. Aim of my project is the characterization of sex-related proteins of different brown algal species. Two species were chosen for the project: Ectocarpus siliculosus and Scytosiphon lomentaria. Both belong to the order Ectocarpales and show several similarities in their life cycle. Proteins of algal gametes were extracted and separated via 2-D SDS gel electrophoresis. First results show that there is a high variability in the comparative patterns of male and female gametes. On the level of the membrane proteins around 30% are expressed differentially. These proteins are supposed to be involved in sexual recognition. For further characterization of these proteins mass spectrometric analysis and de novo sequencing are planned.
(1)Max Planck Institute for Chemical Ecology, Jena, 07745, Germany
(2)Field Science Center for Northern Biosphere, Muroran, Hokkaido, Japan
Peters AF(1), Coelho SMB(1), Cock JM(1) & Bothwell JH(2)
Looking for the genetic basis of sex determination in E. siliculosus
We present preliminary genetic map data towards the first identification of the Ectocarpus siliculosus sex locus. Sex loci are non-recombining genomic regions which have evolved independently and repeatedly across different species to maintain the distinctions between males and females in many animals and flowering plants. These sex determining regions may span entire chromosomes, as with the XY system in humans and some dioecious plants, or they may be limited to the smaller regions which determine mating types in yeast and Chlamydomonas. In contrast to the ever-increasing amount of data on sex-determining regions in animals and plants, no sex-determining locus has been identified in brown macroalgae - an evolutionarily distinct eukaryotic lineage. We are applying the amplified fragment length polymorphism (AFLP) technique to inbred male and female E. siliculosus lines, using a variety of primer pairs to identify molecular markers that co-segregate with sex. These markers will be tested for sex-linkage in other known male and female E. siliculosus lines, with the eventual aim of cloning and locating them on the assembled male E. siliculosus genome sequence.
(1)Station Biologique de Roscoff, Place Georges Tessier, Roscoff, 29682, France
(2)Marine Biological Association, Citadel Hill, Plymouth, PL1 2PB, UK
Ritter A(1),(2), Contreras L(2), Tonon T(1), Correa J(2) & Potin P(1)
Development of proteomic tools and a differential proteome analysis in E. siliculosus submitted to copper stress
As a consequence of human activities, heavy metals have become a common pollution source in marine systems. Along copper polluted areas, few species such as E. siliculosus can tolerate this stress and maintain stable populations. Our project aims to characterise Ectocarpus strains presenting metal tolerance and identify their regulated responses to copper excess by combining proteomic and transcriptomic approaches. The proteomic project had first consisted in the establishment of a phenol based extracting method for suitable proteome analysis. This technique allows to obtain 2DE gels of high quality. We have validated this technique by analysing 150 spots using MALDI-TOF peptide digests fingerprinting. The following peptides fingerprints have been identified by a query on the Ectocarpus genomic data. Following this achievement, we are now undergoing differential 2D analysis, using a copper tolerant strain of E. siliculosus isolated from mine wasted polluted areas in Northen Chile, compared with a more sensitive strain isolated from non polluted areas in Peru.
(1)Station Biologique, UMR 7139 CNRS-UPMC and LIA DIAMS, BP74, 29682, Roscoff, France
(2)CNRS UMR 7193, Laboratoire de Biochimie, Faculté de Médecine de Brest, CS 93837-29238 Brest cédex 3, France
(3)Departamento de Ecología, Center for Advanced Studies in Ecology & Biodiversity, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, LIA DIAMS, Santiago, Chile
Delage L, Ritter A Leblanc C & Potin P
What will we learn about secondary metabolism and defence from the annotation of the Esil genome?
Comparative analysis of the Ectocarpus siliculosus genome has broad implications for state of defence in multicellular heterokonts and the genetic underpinnings of immunity in photosynthetic eukaryotes. Previous hypotheses for the evolution of defence mechanisms in these organisms were based on the collections of a limited number of ESTs from morphologically complex parachymentous brown algal kelps and fucoids. These analyses pointed to several originalities, such as the under-representation of classical antioxidant enzymes and the abundance of transcripts encoding a diversity of haloperoxidase isoforms, some possibly dedicated to Reactive Oxygen Species scavenging. Genes of typical defense-metabolic pathways such as the oxylipin and secondary metabolisms were hardly mined. In contrast, the genome of the filamentous brown alga E. siliculosus features an unexpected complexity of putative receptor proteins with Leucine-Rich Repeats and of important genes in key metabolic pathways are also present, many of which have previously been identified only from higher plants, and some others correspond to genes that are critical in innate immunity of metazoans. The talk will highlight major prospects and will focus on the molecular dissection of the unique metabolism of phenolics in brown algae.
Station Biologique de Roscoff, Place Georges Tessier, Roscoff, 29682, France
Strittmatter M, Gachon CMM & Küpper FC
Development of molecular methods to study the Ectocarpus - Eurychasma pathosystem
The brown algal oomycete pathogen Eurychasma dicksonii has first been described in the 19th century and since then has been mentioned in numerous observations from the field. So far, detection and quantification of this pathogen have been performed using conventional microscopic observation and symptom scoring. Since Eurychasma is an intracellular pathogen, microscopy is difficult and time-consuming, especially if infection density is low. Here we describe the application of a Real-Time PCR assay to detect and quantify oomycete infection in brown algae - using our model system of Ectocarpus siliculosus and Eurychasma dicksonii. We could demonstrate that the assay is suitable to assess the presence of Eurychasma as well as the severity of infection in Ectocarpus. First developed on defined laboratory cultures, this technique is also suitable to accurately monitor the prevalence and abundance of pathogens in natural algal populations in the field. The assay has been used to screen the susceptibility of 45 Ectocarpus strains to disease. We could observe that the severity of Eurychasma infection in Ectocarpus varies with Ectocarpus strains showing no symptoms as well as strains being highly susceptible towards the pathogen. A comparative proteomic approach using two-dimensional electrophoresis will address the question of resistance-related proteins in Ectocarpus.
Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll, PA37 1QA, UK
Gachon CMM(1), Müller DG(2), Strittmatter M(1) & Küpper FC(1)
A conserved immune response of brown algae against the oomycete pathogen Eurychasma dicksonii?
The seaweed oomycete pathogen Eurychasma dicksonii is most abundant eukaryotic pathogen of marine brown algae, and also the most basal member of the oomycete lineage. We currently hold over 330 Ectocarpus and 10 Eurychasma strains from all over the world, most of them being freely available from the Culture Collection for Algae and Protozoa (http://www.ccap.ac.uk/). We have set up a pathosystem between the Eurychasma and the genomic brown algal model Ectocarpus siliculosus. Our results show that the reaction of different algal strains against Eurychasma range from extreme susceptibility to complete resistance against infection. In all cases investigated, resistance is associated with the early death of the challenged algal cell, which prevents further spread of the disease. The most frequent infection outcome however is an intermediate resistance phenotype, whereby a fraction of algal cells get successfully infected, whereas others undergo cell death before the pathogen completes its development cycle. Significantly, we have observed such responses in 8 different algal species, encompassing 4 brown algal orders (Ectocarpales, Laminariales, Tilopteridales, Discosporangiales). This broad distribution suggests that resistance-associated cell death might be a conserved immune mechanism of brown algae. We are now focusing our efforts on the molecular characterization of this cell death response in Ectocarpus and related species, testing the hypothesis that it might be the outcome of a genetically-programmed mechanism similar to animal apoptosis or the hypersensitive response in higher plants.
(1)Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll, PA37 1QA, UK
(2)Fachbereich Biologie der Universität, D-78457, Konstanz, Germany
Küpper FC
Iodide accumulation in brown algae
Brown algae of the Laminariales (kelps) are the strongest accumulators of iodine among living organisms. They represent a major pump in the global biogeochemical cycle of iodine and in particular, the major source of iodocarbons in the coastal atmosphere. Nevertheless, the chemical state and biological significance of accumulated iodine have remained unknown to this date. Using X-ray absorption spectroscopy, we show that the accumulated form is iodide, which readily scavenges a variety of reactive oxygen species. We propose here that its biological role is that of an inorganic antioxidant, the first to be described in a living system. Upon oxidative stress, iodide is effluxed. On the thallus surface and in the apoplast, iodide detoxifies both aqueous oxidants and ozone, the latter resulting in the release of high levels of molecular iodine and consequent formation of hygroscopic iodine oxides leading to particles, which are precursors to cloud condensation nuclei.- In contrast to Laminaria and a few other Phaeophyta with complex morphologies, virtually nothing is known about iodine metabolism in Ectocarpus and filamentous brown algal species. Preliminary results show that Ectocarpus also accumulates iodine as iodide, albeit at lower levels than Laminaria.
CCAP, Dunstaffnage Marine Laboratory, Dunbeg, Oban, Argyll, PA37 1QA, UK
Session 4: Developmental biology
Chair: M Cock
Billoud B(1), Le Bail A(2) & Charrier B(2)
Ectomat, a computer simulation of the developmental patterning of the early sporophyte of Ectocarpus siliculosus
During the early sporophyte development of E. siliculosus, a linear primary filament (PF) is built up and serves as a basis for the whole alga morphogenesis. Deciphering these initial steps (gamete to 10 cells) addresses fundamental issues in multi-cellular development like cell differentiation and communication. We define two main cell types: round (R) and elongated (E). They form a polymorphic positional pattern, which we show to statistically differ from a random arrangement. We have tested the hypothesis that building this global pattern can be achieved by locally controlled processes. To do so, observations of growing sporophytes lead to the identification of five different events of division and differentiation. The sporophyte development is then modelled by a stochastic automaton (Ectomat), in which these events are postulated to randomly occur in cells, depending only on their type (E or R) and on their immediate neighbours. Ectomat is able to reconstruct most of the essential properties of the early PF growth and patterning. We conclude that randomly occurring cell events, driven by local information exchange between adjacent cells may be sufficient to account for the early sporophyte development and cell-type patterning, which ultimately ensures the overall radial symmetry of E. siliculosus.
(1)UPMC University of Paris 06, Atelier de Bioinformatique, MB1202, 75252, Paris cedex 05, France
(2)CNRS, UMR 7139, Station Biologique, Place Georges Tessier, 29682, Roscoff, France
Coelho SM, Peters AF, Scornet D & Cock JM
The OUROBOROS mutant of Ectocarpus siliculosus exhibits homeotic conversion of the sporophyte into a gametophyte
Our aim is to identify and characterize the key regulatory mechanisms that initiate and control the haploid-diploid life cycle of Ectocarpus. One of the strategies we are using is to screen for mutations that cause deployment of the "wrong" developmental program at a particular stage of the life cycle. The first mutant we have isolated, immediate upright (imm), has a sporophyte that exhibits several features typical of the gametophyte. However, functionally, it remains a sporophyte (Peters et al. 2008). The second mutant, ouroboros (oro), exhibits a complete functional conversion of the sporophyte into a gametophyte. oro has been analysed genetically and shown to be recessive, single locus, Mendelian locus. Oro and imm have been crossed and the mutations were found unlinked and located in different loci. A detailed genetic map of Ectocarpus is now in progress in the laboratory and the positional cloning of the oro mutation is currently under way using an AFLP approach. Additionally, we have indications that switching between generations can be influenced by non-cell-autonomous factors. Interestingly, the sporophyte seems to emit a signal that induces developmental reprogramming in gametophyte protoplasts. In contrast, sporophyte protoplasts are not influenced by the presence of gametophytes and this is consistent with our genetic analysis, which suggests that the gametophyte may be the default state.
Station Biologique de Roscoff, Place Georges Tessier, Roscoff, 29682, France
Kimura K, Nagasato C & Motomura T
Cytoplasmic inheritance of mitochondria in brown algae
Maternal inheritance of mitochondria has been reported in oogamous and isogamous members in brown algae. In Laminaria angustata (oogamy), ultrastructural observations clearly showed that sperm mitochondria were digested with lysosomes in zygote after fertilization. However, in isogamous algae, Ectocarpus siliculosus and Scytosiphon lomentaria, the maternal inheritance of mitochondria was only indicated using the molecular markers of mitochondria DNA (mtDNA). Therefore, deletion mechanisms of the paternal mitochondria or mtDNA in the zygotes have not been clarified. In this study, we examined when the mtDNA derived from the male gamete disappears, and examined the number and morphology of mitochondria during the zygote development after fertilization in S. lomentaria. Consequently, we clarified that the paternal mtDNA disappeared during 4 to 7-celled stages of zygotes (sporophytes). The number of mitochondria did not change until 2-celled stage of zygotes. During the zygote development, mitochondria did not fuse each other, nor branch, and were not digested in lysosomes. These results suggested that the male mitochondria were not digested in the early zygotes, different from the case of oomamous members. It is expected that the isogamous members of brown algae will have a different system on deletion of the paternal mitochondria or mtDNA.
Muroran Marine Station, Field Science Center for Northern Hemisphere, Hokkaido University, Muroran, 051-003, Japan
Le Bail A, Maisonneuve C, Cho GY, Cock JM & Charrier B
Genetic characterisation of branching mutants in Ectocarpus siliculosus
The developmental processes involved in the early morphogenesis of the sporophytes of the brown algae Ectocarpus siliculosus are under study. We showed that the morphogenetic pattern is the result of the interplay of three processes, i.e. the apical growth, the distribution of two different cell types along the filament, and the position of emergence of the branches, which are controlled by endogenous mechanisms (Le Bail et al., J Phycol., in press). A series of ~ 20 mutants displaying alterations in their branching pattern were selected after UVB irradiation. Among them, the mutants late branching increase (lbi) and asparagus (asp) were chosen for further investigation. We will present the detailed feature of the morphological alterations of lbi and asp, and will describe their genetic analysis. These mutants were crossed with a compatible wild type isolate. Microsatellite polymorphism was used to check the heterozygous character of the F1 individuals, and comparisons of the phenotype of the F1 with both parents and control crosses will indicate the recessive/dominant character of the mutation. Meiosis products are currently analysed in order to determine the number of loci. Further genetic analyses are underway, especially the creation of complementation groups among these 20 branching mutants. In parallel, the expression pattern of lbi and asp will be analysed by microarray.
Station Biologique de Roscoff, Place Georges Tessier, Roscoff, 29682, France
(author for correspondence: B Charrier)
Nagasato C & Motomura T
Two membrane systems involved in cytokinesis of brown algae
In brown algae, cytokinesis proceeds at the crossing region of microtubules (MTs) from centrosomes near daughter nuclei. New cell partition membrane is formed by fusion of Golgi vesicles and flat cisternae. Golgi vesicles are transported by MTs, however, it remains unclear how flat cisternae develop and arrange at the cytokinetic plane. Brown algae have the particular actin structure like a plate at the future cytokinetic plane, and pharmacological experiments using cytochalasin, and latrunculin B (LB) have indicated that depolymerization of actin filaments inhibits the progression of cytokinesis. In this study, the origin of the flat cisternae and the effect of actin filaments on the behavior of the flat cisternae were examined in zygotes of Silvetia babingtonii and Scytosiphon lomentaria. Ultrastructures in these zygotes treated with LB showed that the development of flat cisternae was completely blocked, therefore, the new cell partition membrane was not formed. From observations of Silvetia zygotes, the flat cisternae would be derived from ER lying between daughter nuclei, and actin filaments would involve in production of the flat cisternae. Moreover, experiments using brefeldin A showed that flat cisternae were necessary to complete the new cell partition membrane, and Golgi vesicles supplied the cell wall material.
Muroran Marine Station, Field Science Center for Northern Hemisphere, Hokkaido University, Muroran, 051-003, Japan
Session 5: Biodiversity & evolution
Chair: H Kawai (tbc)
Le Corguillé G(1), Pearson G(2), Valente M(2), Viegas C(2), Gschlößl B(3), Corre E(1), Peters A(3), Jubin C(4), Vacherie B(4), Cock M(3) & Leblanc C(3)
Chloroplast genomes of two brown algae, Ectocarpus siliculosus and Fucus vesiculosus: further insights into chromist plastid evolution
The chloroplast genomes (cpDNA) of two brown algae, Ectocarpus siliculosus and Fucus vesiculosus, have been completely sequenced. They represent the first plastid genomes fully characterized from two distinct orders of Phaeophyceae, which belong to the heterokont lineage. The sizes of these two circular plastid genomes are 139,954 bp and 125,044 base pairs, respectively, with longer inverted repeat regions in E. siliculosus cpDNA. Gene contents and rearrangements are very similar between the two genomes with 140-148 protein-coding genes, 27-31 tRNA genes, and 3 ribosomal RNA genes. In F. vesiculosus cpDNA, one intron has been located in the tRNA-Leu gene, but no intronic sequence has been found in the homologous gene of E. siliculosus cpDNA, suggesting its recent loss in Ectocarpales. Within the eukaryotic supergroup of Chromalveolates, heterokont algae, together with cryptophytes and haptophytes, possess red-algal derivated plastids. Due to incongruences between nuclear and plastid phylogenies, the hypothesis of a monophyletic origin for chromist plastids derived from a single secondary endosymbiotic event is a challenging question that remains under debate. In this evolutionary context, phylogenetic analyses were conducted with a data set of 44 concatenated proteins from 2 cyanobacterial genomes and 17 plastid genomes, including all the available red algal and chromist plastid genomes. Plastid phylogenetic trees, which clearly support the monophyly of heterokonts, are discussed in the light of recent nuclear phylogenetic studies.
(1)CNRS, UPMC University of Paris 6, FR2424, Computer and Genomics Resource Centre, Station Biologique, 29682, Roscoff, France
(2)Marine Ecology and Evolution, Centre of Marine Sciences, University of Algarve, Gambelas, 8005-139, Faro, Portugal
(3)CNRS, UPMC University of paris 6, UMR 7139, Marine Plants and Biomolecules, Station Biologique, 29682, Roscoff, France
(4)Genoscope CEA, 2 rue Gaston Crémieux, 91000, Evry, France
Taskin E & Ozturk M
The genus Ectocarpus of Turkey
In this study 6 species of brown algal genus Ectocarpus (Phaeophyceae, Ectocarpaceae) collected along the coasts of the Aegean Sea, Sea of Dardanelles and Mediterranean Sea, Turkey, were reported: Ectocarpus fasciculatus, E. siliculosus var. siliculosus, E. siliculosus var. crouaniorum, E. siliculosus var. dasycarpus, E. siliculosus var. hiemalis and E. siliculosus var. penicillatus. Data concerning geographical distribution, morphology and ecology of each species were given too.
Department of Biology, Faculty of Arts and Sciences, Celal Bayar University, Muradiye-Manisa, 45140, Turkey
Peters AF
The MBA project "Ectocarpus in Britain"
To better understand the taxonomy and natural diversity of Ectocarpus I am presently studying the species in Great Britain. The project is being executed in 2008-9 and is funded by the Marine Biological Association of the United Kingdom (MBA, Plymouth). A number of key field sites are being visited in the different regions of the United Kingdom, replicate samples taken and laboratory cultures initiated. Genetic analyses and crossing studies are expected to reveal the number of major genotype clusters present in Britain; these may deserve species rank. Samples from known alien hotspots may show whether exotic genotypes have immigrated recently. The project is expected to provide easy-to-use molecular markers for future species identification.
Bezhin Rosko, 28 hent Perharidy, 29680, Rosko, France
Yamagishi T(1), Hanyuda T(1), Takagi R(1), Müller DG(2) & Kawai H(1)
Structural diversity of the EcOcm3 gene introns in Ectocarpus spp.
The morphological and genetic diversity of the tubular mastigoneme, one of the distinctive cell structure characteristic to the stramenopiles (Heterokontophyta), is considered to become an effective tool for elucidating the phylogeny of stramenopiles. In previous study, we identified the mastigoneme-related protein Ocm1 in a chrysophycean alga Ochromonas danica. The genes Ocm2 and Ocm3 belonging to the same gene family as Ocm1 were also determined in O. danica. In Phaeophyceae, the gene sequence of Ocm3 included three introns, and their insertion positions were highly conserved. In contrast, the DNA sequences of the introns were rather variable. In this study, we compared the intron DNA sequences of the Ectocarpus Ocm3 (EcOcm3) for elucidating the species-level phylogeny of the genus. The intron types of EcOcm3 were classified into 16 types characterized by the gaps inserted or deleted within the introns. These intron types generally corresponded to the major clades revealed from the molecular phylogenetic analysis based on the sequences of the introns as well as the mitochondrial cox3 gene.
(1)Research Center for Inland Seas, Kobe University, Kobe, 657-8501, Japan
(2)University of Konstanz, Konstanz, Germany
Culture Collection of Algae and Protozoa (CCAP)
Dunstaffnage Marine Laboratory • Dunbeg • Oban • PA37 1QA • UK
Tel: +44 (0)1631 559000 • Fax: +44 (0)1631 559001 • Email: ccap@sams.ac.uk • Web: www.ccap.ac.uk
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