title: Downregulation of a putative plastid PDC E1α subunit impairs photosynthetic activity and triacylglycerol accumulation in nitrogen-starved photoautotrophic Chlamydomonas reinhardtii.
abstract: The chloroplast pyruvate dehydrogenase complex (cpPDC) catalyses the oxidative decarboxylation of pyruvate forming acetyl-CoA, an immediate primer for the initial reactions of de novo fatty acid (FA) synthesis. Little is known about the source of acetyl-CoA in the chloroplasts of photosynthetic microalgae, which are capable of producing high amounts of the storage lipid triacylglycerol (TAG) under conditions of nutrient stresses. We generated Chlamydomonas reinhardtii CC-1618 mutants with decreased expression of the PDC2_E1α gene, encoding the putative chloroplast pyruvate dehydrogenase subunit E1α, using artificial microRNA. A comparative study on the effects of PDC2_E1α silencing on FAs and TAG production in C. reinhardtii, grown photoautotrophically and mixotrophically, with and without a nitrogen source in the nutrient medium, was carried out. Reduced expression of PDC2 _E1α led to a severely hampered photoautotrophic growth phenotype with drastic impairment in TAG accumulation under nitrogen deprivation. In the presence of acetate, downregulation of PDC2_E1α exerted little to no effect on TAG production and photosynthetic activity. In contrast, under photoautotrophic conditions, especially in the absence of a nitrogen source, a dramatic decline in photosynthetic oxygen evolution and photosystem II quantum yield against a background of the apparent over-reduction of the photosynthetic electron chain was recorded. Our results suggest an essential role of cpPDC in the supply of carbon precursors for de novo FA synthesis in microalgae under conditions of photoautotrophy. A shortage of this supply is detrimental to the nitrogen-starvation-induced synthesis of storage TAG, an important carbon and energy sink in stressed Chlamydomonas cells, thereby impairing the acclimation ability of the microalga.
authors.affiliation: Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel.
authors.forename: Nastassia
authors.initials: N
authors.lastname: Shtaida
authors.affiliation: Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel khozin@bgu.ac.il.
authors.forename: Inna
authors.initials: I
authors.lastname: Khozin-Goldberg
authors.affiliation: Department of Bioengineering, Faculty of Biology, Moscow State University, 119234, GSP-1 Moscow, Russia.
authors.forename: Alexei
authors.initials: A
authors.lastname: Solovchenko
authors.affiliation: Department of Bioengineering, Faculty of Biology, Moscow State University, 119234, GSP-1 Moscow, Russia.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Chekanov
authors.affiliation: Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel.
authors.forename: Shoshana
authors.initials: S
authors.lastname: Didi-Cohen
authors.affiliation: Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel.
authors.forename: Stefan
authors.initials: S
authors.lastname: Leu
authors.affiliation: Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel.
authors.forename: Zvi
authors.initials: Z
authors.lastname: Cohen
authors.affiliation: Microalgal Biotechnology Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel.
authors.forename: Sammy
authors.initials: S
authors.lastname: Boussiba
mesh_terms: D052818:Autotrophic Processes / Q000528:radiation effects; D018533:Biomass; D002338:Carotenoids / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D019295:Computational Biology; D015536:Down-Regulation / Q000528:radiation effects; D005227:Fatty Acids / Q000378:metabolism; D020868:Gene Silencing; D017343:Genes, Plant; D008027:Light; D009584:Nitrogen / Q000172:deficiency; D010788:Photosynthesis / Q000528:radiation effects; D018087:Plastids / Q000201:enzymology* / Q000528:radiation effects; D030481:Pyruvate Dehydrogenase (Lipoamide) / Q000378:metabolism*; D014170:Transformation, Genetic; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D005227:Fatty Acids; D014280:Triglycerides; D002338:Carotenoids; D030481:Pyruvate Dehydrogenase (Lipoamide); C065640:pyruvate dehydrogenase E1alpha subunit; D009584:Nitrogen
keywords: Acetyl-CoA; chlorophyll fluorescence transients; fatty acid synthesis; lipid; microalgae; photosystem II; pyruvate dehydrogenase.