title: Remodeling of intermediate metabolism in the diatom Phaeodactylum tricornutum under nitrogen stress.
abstract: Diatoms are unicellular algae that accumulate significant amounts of triacylglycerols as storage lipids when their growth is limited by nutrients. Using biochemical, physiological, bioinformatics, and reverse genetic approaches, we analyzed how the flux of carbon into lipids is influenced by nitrogen stress in a model diatom, Phaeodactylum tricornutum. Our results reveal that the accumulation of lipids is a consequence of remodeling of intermediate metabolism, especially reactions in the tricarboxylic acid and the urea cycles. Specifically, approximately one-half of the cellular proteins are cannibalized; whereas the nitrogen is scavenged by the urea and glutamine synthetase/glutamine 2-oxoglutarate aminotransferase pathways and redirected to the de novo synthesis of nitrogen assimilation machinery, simultaneously, the photobiological flux of carbon and reductants is used to synthesize lipids. To further examine how nitrogen stress triggers the remodeling process, we knocked down the gene encoding for nitrate reductase, a key enzyme required for the assimilation of nitrate. The strain exhibits 40-50% of the mRNA copy numbers, protein content, and enzymatic activity of the wild type, concomitant with a 43% increase in cellular lipid content. We suggest a negative feedback sensor that couples photosynthetic carbon fixation to lipid biosynthesis and is regulated by the nitrogen assimilation pathway. This metabolic feedback enables diatoms to rapidly respond to fluctuations in environmental nitrogen availability.
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences and levitan@marine.rutgers.edu falko@marine.rutgers.edu.
authors.forename: Orly
authors.initials: O
authors.lastname: Levitan
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences and.
authors.forename: Jorge
authors.initials: J
authors.lastname: Dinamarca
authors.affiliation: Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901;
authors.forename: Ehud
authors.initials: E
authors.lastname: Zelzion
authors.affiliation: Center for Computational and Integrative Biology, Rutgers University, Camden, NJ 08102; Phenomics and Bioinformatics Research Centre and School of Mathematics and Statistics, University of South Australia, Mawson Lakes, South Australia 5095, Australia;
authors.forename: Desmond S
authors.initials: DS
authors.lastname: Lun
authors.affiliation: Department of Chemistry, Princeton University, Princeton, NJ 08544;
authors.forename: L Tiago
authors.initials: LT
authors.lastname: Guerra
authors.affiliation: Center for Computational and Integrative Biology, Rutgers University, Camden, NJ 08102;
authors.forename: Min Kyung
authors.initials: MK
authors.lastname: Kim
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences and.
authors.forename: Joomi
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543; and.
authors.forename: Benjamin A S
authors.initials: BA
authors.lastname: Van Mooy
authors.affiliation: Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901;
authors.forename: Debashish
authors.initials: D
authors.lastname: Bhattacharya
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences and Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854 levitan@marine.rutgers.edu falko@marine.rutgers.edu.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Falkowski
mesh_terms: D017377:Diatoms / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D055785:Gene Knockdown Techniques; D050356:Lipid Metabolism; D064688:Metabolic Flux Analysis; D053858:Metabolic Networks and Pathways; D008954:Models, Biological; D050901:Nitrate Reductase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D050901:Nitrate Reductase; D009584:Nitrogen
keywords: NR; RNAi; lipid; metabolism; stress