title: Ostreococcus tauri is a new model green alga for studying iron metabolism in eukaryotic phytoplankton.
abstract: Low iron bioavailability is a common feature of ocean surface water and therefore micro-algae developed original strategies to optimize iron uptake and metabolism. The marine picoeukaryotic green alga Ostreococcus tauri is a very good model for studying physiological and genetic aspects of the adaptation of the green algal lineage to the marine environment: it has a very compact genome, is easy to culture in laboratory conditions, and can be genetically manipulated by efficient homologous recombination. In this study, we aimed at characterizing the mechanisms of iron assimilation in O. tauri by combining genetics and physiological tools. Specifically, we wanted to identify and functionally characterize groups of genes displaying tightly orchestrated temporal expression patterns following the exposure of cells to iron deprivation and day/night cycles, and to highlight unique features of iron metabolism in O. tauri, as compared to the freshwater model alga Chalamydomonas reinhardtii.
  
  
  
  We used RNA sequencing to investigated the transcriptional responses to iron limitation in O. tauri and found that most of the genes involved in iron uptake and metabolism in O. tauri are regulated by day/night cycles, regardless of iron status. O. tauri lacks the classical components of a reductive iron uptake system, and has no obvious iron regulon. Iron uptake appears to be copper-independent, but is regulated by zinc. Conversely, iron deprivation resulted in the transcriptional activation of numerous genes encoding zinc-containing regulation factors. Iron uptake is likely mediated by a ZIP-family protein (Ot-Irt1) and by a new Fea1-related protein (Ot-Fea1) containing duplicated Fea1 domains. The adaptation of cells to iron limitation involved an iron-sparing response tightly coordinated with diurnal cycles to optimize cell functions and synchronize these functions with the day/night redistribution of iron orchestrated by ferritin, and a stress response based on the induction of thioredoxin-like proteins, of peroxiredoxin and of tesmin-like methallothionein rather than ascorbate. We briefly surveyed the metabolic remodeling resulting from iron deprivation.
  
  
  
  The mechanisms of iron uptake and utilization by O. tauri differ fundamentally from those described in C. reinhardtii. We propose this species as a new model for investigation of iron metabolism in marine microalgae.
authors.affiliation: CNRS, Institut Jacques Monod, Université Paris Diderot-Paris 7, F-75013, Paris, France.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Lelandais
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University in Prague, 12844, Prague, Czech Republic.
authors.forename: Ivo
authors.initials: I
authors.lastname: Scheiber
authors.affiliation: Ecole Normale Supérieure, PSL Research University, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), CNRS UMR 8197, INSERM U1024, 46 rue d'Ulm, F-75005, Paris, France.
authors.forename: Javier
authors.initials: J
authors.lastname: Paz-Yepes
authors.affiliation: Sorbonne Universités, University Pierre et Marie Curie, University of Paris VI, CNRS, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, F-66650, Banyuls-sur-Mer, France.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Lozano
authors.affiliation: Sorbonne Universités, University Pierre et Marie Curie, University of Paris VI, CNRS, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, F-66650, Banyuls-sur-Mer, France.
authors.forename: Hugo
authors.initials: H
authors.lastname: Botebol
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University in Prague, 12844, Prague, Czech Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Pilátová
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University in Prague, 12844, Prague, Czech Republic.
authors.forename: Vojtěch
authors.initials: V
authors.lastname: Žárský
authors.affiliation: CNRS, Institut Jacques Monod, Université Paris Diderot-Paris 7, F-75013, Paris, France.
authors.forename: Thibaut
authors.initials: T
authors.lastname: Léger
authors.affiliation: Sorbonne Universités, University Pierre et Marie Curie, University of Paris VI, CNRS, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, F-66650, Banyuls-sur-Mer, France.
authors.forename: Pierre-Louis
authors.initials: PL
authors.lastname: Blaiseau
authors.affiliation: Ecole Normale Supérieure, PSL Research University, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), CNRS UMR 8197, INSERM U1024, 46 rue d'Ulm, F-75005, Paris, France.
authors.forename: Chris
authors.initials: C
authors.lastname: Bowler
authors.affiliation: Sorbonne Universités, University Pierre et Marie Curie, University of Paris VI, CNRS, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, F-66650, Banyuls-sur-Mer, France.
authors.forename: François-Yves
authors.initials: FY
authors.lastname: Bouget
authors.affiliation: CNRS, Institut Jacques Monod, Université Paris Diderot-Paris 7, F-75013, Paris, France.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Camadro
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University in Prague, 12844, Prague, Czech Republic. sutak@natur.cuni.cz.
authors.forename: Robert
authors.initials: R
authors.lastname: Sutak
authors.affiliation: CNRS, Institut Jacques Monod, Université Paris Diderot-Paris 7, F-75013, Paris, France. emmanuel.lesuisse@ijm.fr.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Lesuisse
mesh_terms: D000220:Adaptation, Biological; D000460:Chlorophyta / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D016000:Cluster Analysis; D003300:Copper / Q000378:metabolism; D056890:Eukaryota / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000528:radiation effects; D059014:High-Throughput Nucleotide Sequencing; D006706:Homeostasis; D007501:Iron / Q000378:metabolism*; D058085:Iron Compounds / Q000378:metabolism; D010084:Oxidation-Reduction; D017440:Photoperiod; D010802:Phylogeny; D010839:Phytoplankton / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013312:Stress, Physiological; D059467:Transcriptome
chemical_list: D058085:Iron Compounds; D010940:Plant Proteins; D003300:Copper; D007501:Iron
keywords: Iron; Marine phytoplankton; Ostreococcus; RNA-seq analysis