Browsing by Author "Kloareg, Bernard"

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    Spore release in Acrochaetium sp (Rhodophyta) is bacterially controlled
    (2007) Weinberger, Florian; Beltran, Jessica; Correa, Juan A.; Lion, Ulrich; Pohnert, Georg; Kumar, Naresh; Steinberg, Peter; Kloareg, Bernard; Potin, Philippe
    The facultative red algal epiphyte Acrochaetium sp. liberated spores preferentially and recruited more successfully in laboratory cultures when its host Gracilaria chilensis C. J. Bird, McLachlan et E. C. Oliveira was present. The same effect was also induced by cell-free medium from G. chilensis, suggesting it contained a molecular signal. Antibiotics prevented spore release in Acrochaetium sp., even when G. chilensis was present, suggesting a prokaryotic origin of the signal. Simultaneous application of N-butyl-homoserine-lactone (BHL) restored the spore-release capacity, which demonstrated that spore release was not directly inhibited by the antibiotics and indicated that bacterially generated N-acyl-homoserine-lactones (AHLs) regulate spore release. An involvement of AHL was further indicated by the fact that two different halofuranone inhibitors of AHL receptors also inhibited spore release when they were applied at relatively low concentrations. Of seven different AHLs tested, only BHL induced the effect. However, BHL was only active at relatively high concentrations (100 mu M), and it was not detected in spore-release-inducing medium of G. chilensis. Another water-soluble AHL or an AHL structure analog is therefore probably the active compound in G. chilensis cultures. The data presented demonstrate that life cycle completion in Acrochaetium sp. strongly depends on bacteria, which are not always present in sufficient numbers on the alga itself. Exogenous bacteria that are associated with G. chilensis or with other potential substrates may therefore trigger timely spore liberation in Acrochaetium sp., provided that the necessary concentration of AHL is reached. This first finding of AHL perception in a red alga confirms that AHL signalling is more widespread among eukaryotes than was thought until recently. However, spore release of a second red alga, Sahlingia subintegra (Rosenv.) Kornmann, was unaffected by AHL, and the reaction observed is therefore not universal.
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    The Ectocarpus genome and the independent evolution of multicellularity in brown algae
    (2010) Cock, J. Mark; Sterck, Lieven; Rouze, Pierre; Scornet, Delphine; Allen, Andrew E.; Amoutzias, Grigoris; Anthouard, Veronique; Artiguenave, Francois; Aury, Jean-Marc; Badger, Jonathan H.; Beszteri, Bank; Billiau, Kenny; Bonnet, Eric; Bothwell, John H.; Bowler, Chris; Boyen, Catherine; Brownlee, Colin; Carrano, Carl J.; Charrier, Benedicte; Cho, Ga Youn; Coelho, Susana M.; Collen, Jonas; Corre, Erwan; Da Silva, Corinne; Delage, Ludovic; Delaroque, Nicolas; Dittami, Simon M.; Doulbeau, Sylvie; Elias, Marek; Farnham, Garry; Gachon, Claire M. M.; Gschloessl, Bernhard; Heesch, Svenja; Jabbari, Kamel; Jubin, Claire; Kawai, Hiroshi; Kimura, Kei; Kloareg, Bernard; Kuepper, Frithjof C.; Lang, Daniel; Le Bail, Aude; Leblanc, Catherine; Lerouge, Patrice; Lohr, Martin; Lopez, Pascal J.; Martens, Cindy; Maumus, Florian; Michel, Gurvan; Miranda-Saavedra, Diego; Morales, Julia; Moreau, Herve; Motomura, Taizo; Nagasato, Chikako; Napoli, Carolyn A.; Nelson, David R.; Nyvall-Collen, Pi; Peters, Akira F.; Pommier, Cyril; Potin, Philippe; Poulain, Julie; Quesneville, Hadi; Read, Betsy; Rensing, Stefan A.; Ritter, Andres; Rousvoal, Sylvie; Samanta, Manoj; Samson, Gaelle; Schroeder, Declan C.; Segurens, Beatrice; Strittmatter, Martina; Tonon, Thierry; Tregear, James W.; Valentin, Klaus; von Dassow, Peter; Yamagishi, Takahiro; Van de Peer, Yves; Wincker, Patrick
    Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related(1). These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1). We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae(2-5), closely related to the kelps(6,7) (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic(2) approaches to explore these and other(4,5) aspects of brown algal biology further.