| Autor: |
Levitan O; Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences and levitan@marine.rutgers.edu falko@marine.rutgers.edu., Dinamarca J; Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences and., Zelzion E; Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901;, Lun DS; 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;, Guerra LT; Department of Chemistry, Princeton University, Princeton, NJ 08544;, Kim MK; Center for Computational and Integrative Biology, Rutgers University, Camden, NJ 08102;, Kim J; Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences and., Van Mooy BA; Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543; and., Bhattacharya D; Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901;, Falkowski PG; 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. |
| Abstrakt: |
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. |
