title: Auxin metabolism and function in the multicellular brown alga Ectocarpus siliculosus.
abstract: Ectocarpus siliculosus is a small brown alga that has recently been developed as a genetic model. Its thallus is filamentous, initially organized as a main primary filament composed of elongated cells and round cells, from which branches differentiate. Modeling of its early development suggests the involvement of very local positional information mediated by cell-cell recognition. However, this model also indicates that an additional mechanism is required to ensure proper organization of the branching pattern. In this paper, we show that auxin indole-3-acetic acid (IAA) is detectable in mature E. siliculosus organisms and that it is present mainly at the apices of the filaments in the early stages of development. An in silico survey of auxin biosynthesis, conjugation, response, and transport genes showed that mainly IAA biosynthesis genes from land plants have homologs in the E. siliculosus genome. In addition, application of exogenous auxins and 2,3,5-triiodobenzoic acid had different effects depending on the developmental stage of the organism, and we propose a model in which auxin is involved in the negative control of progression in the developmental program. Furthermore, we identified an auxin-inducible gene called EsGRP1 from a small-scale microarray experiment and showed that its expression in a series of morphogenetic mutants was positively correlated with both their elongated-to-round cell ratio and their progression in the developmental program. Altogether, these data suggest that IAA is used by the brown alga Ectocarpus to relay cell-cell positional information and induces a signaling pathway different from that known in land plants.
authors.affiliation: CNRS-Université Pierre et Marie Curie, UMR 7139 Marine Plants and Biomolecules, and Platform of Cytology, CNRS FR2424, Station Biologique de Roscoff, 29682 Roscoff Cedex, France.
authors.forename: Aude
authors.initials: A
authors.lastname: Le Bail
authors.forename: Bernard
authors.initials: B
authors.lastname: Billoud
authors.forename: Nathalie
authors.initials: N
authors.lastname: Kowalczyk
authors.forename: Mariusz
authors.initials: M
authors.lastname: Kowalczyk
authors.forename: Morgane
authors.initials: M
authors.lastname: Gicquel
authors.forename: Sophie
authors.initials: S
authors.lastname: Le Panse
authors.forename: Sarah
authors.initials: S
authors.lastname: Stewart
authors.forename: Delphine
authors.initials: D
authors.lastname: Scornet
authors.forename: Jeremy Mark
authors.initials: JM
authors.lastname: Cock
authors.forename: Karin
authors.initials: K
authors.lastname: Ljung
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Charrier
mesh_terms: D000595:Amino Acid Sequence; D007210:Indoleacetic Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D009024:Morphogenesis; D009154:Mutation; D000459:Phaeophyceae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D007210:Indoleacetic Acids