title: An RNA interference knock-down of nitrate reductase enhances lipid biosynthesis in the diatom Phaeodactylum tricornutum.
abstract: When diatoms are stressed for inorganic nitrogen they remodel their intermediate metabolism and redirect carbon towards lipid biosynthesis. However, this response comes at a significant cost reflected in decreased photosynthetic energy conversion efficiency and growth. Here we explore a molecular genetics approach to restrict the assimilation of inorganic nitrogen by knocking down nitrate reductase (NR). The transformant strain, NR21, exhibited about 50% lower expression and activity of the enzyme but simultaneously accumulated over 40% more fatty acids. However, in contrast to nitrogen-stressed wild-type (WT) cells, which grow at about 20% of the rate of nitrogen-replete cells, growth of NR21 was only reduced by about 30%. Biophysical analyses revealed that the photosynthetic energy conversion efficiency of photosystem II was unaffected in NR21; nevertheless, the plastoquinone pool was reduced by 50% at the optimal growth irradiance while in the WT it was over 90% oxidized. Further analyses reveal a 12-fold increase in the glutamate/glutamine ratio and an increase NADPH and malonyl-CoA pool size. Transcriptomic analyses indicate that the knock down resulted in changes in the expression of genes for lipid biosynthesis, as well as the expression of specific transcription factors. Based on these observations, we hypothesize that the allocation of carbon and reductants in diatoms is controlled by a feedback mechanism between intermediate metabolites, the redox state of the plastid and the expression and binding of transcription factors related to stress responses.
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, 08901, USA.
authors.forename: Orly
authors.initials: O
authors.lastname: Levitan
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, 08901, USA.
authors.forename: Jorge
authors.initials: J
authors.lastname: Dinamarca
authors.affiliation: Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ, 09801, USA.
authors.forename: Ehud
authors.initials: E
authors.lastname: Zelzion
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, 08901, USA.
authors.forename: Maxim Y
authors.initials: MY
authors.lastname: Gorbunov
authors.affiliation: Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, 08901, USA.|Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, 08854, USA.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Falkowski
mesh_terms: D002244:Carbon / Q000378:metabolism; D017377:Diatoms / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D050356:Lipid Metabolism / Q000235:genetics*; D008316:Malonyl Coenzyme A / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D009249:NADP / Q000378:metabolism; D050901:Nitrate Reductase / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism; D010084:Oxidation-Reduction; D010788:Photosynthesis; D034622:RNA Interference; D013312:Stress, Physiological
chemical_list: D009566:Nitrates; D005973:Glutamine; D018698:Glutamic Acid; D008316:Malonyl Coenzyme A; D009249:NADP; D002244:Carbon; D050901:Nitrate Reductase; D009584:Nitrogen
keywords: GSE67449; Phaeodactylum tricornutum; RNAi; lipids; nitrate reductase; photosynthesis