title: A galactoglycerolipid lipase is required for triacylglycerol accumulation and survival following nitrogen deprivation in Chlamydomonas reinhardtii.
abstract: Following N deprivation, microalgae accumulate triacylglycerols (TAGs). To gain mechanistic insights into this phenomenon, we identified mutants with reduced TAG content following N deprivation in the model alga Chlamydomonas reinhardtii. In one of the mutants, the disruption of a galactoglycerolipid lipase-encoding gene, designated PLASTID GALACTOGLYCEROLIPID DEGRADATION1 (PGD1), was responsible for the primary phenotype: reduced TAG content, altered TAG composition, and reduced galactoglycerolipid turnover. The recombinant PGD1 protein, which was purified from Escherichia coli extracts, hydrolyzed monogalactosyldiacylglycerol into its lyso-lipid derivative. In vivo pulse-chase labeling identified galactoglycerolipid pools as a major source of fatty acids esterified in TAGs following N deprivation. Moreover, the fatty acid flux from plastid lipids to TAG was decreased in the pgd1 mutant. Apparently, de novo-synthesized fatty acids in Chlamydomonas reinhardtii are, at least partially, first incorporated into plastid lipids before they enter TAG synthesis. As a secondary effect, the pgd1 mutant exhibited a loss of viability following N deprivation, which could be avoided by blocking photosynthetic electron transport. Thus, the pgd1 mutant provides evidence for an important biological function of TAG synthesis following N deprivation, namely, relieving a detrimental overreduction of the photosynthetic electron transport chain.
authors.affiliation: Department of Energy-Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Li
authors.forename: Eric R
authors.initials: ER
authors.lastname: Moellering
authors.forename: Bensheng
authors.initials: B
authors.lastname: Liu
authors.forename: Cassandra
authors.initials: C
authors.lastname: Johnny
authors.forename: Marie
authors.initials: M
authors.lastname: Fedewa
authors.forename: Barbara B
authors.initials: BB
authors.lastname: Sears
authors.forename: Min-Hao
authors.initials: MH
authors.lastname: Kuo
authors.forename: Christoph
authors.initials: C
authors.lastname: Benning
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000235:genetics* / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D002734:Chlorophyll / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D005816:Genetic Complementation Test; D050356:Lipid Metabolism; D008055:Lipids / Q000032:analysis; D008954:Models, Biological; D009154:Mutation; D009584:Nitrogen / Q000172:deficiency*; D010641:Phenotype; D010788:Photosynthesis; D018087:Plastids / Q000378:metabolism; D011994:Recombinant Proteins; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D020418:Algal Proteins; D005227:Fatty Acids; D008055:Lipids; D011994:Recombinant Proteins; D014280:Triglycerides; D002734:Chlorophyll; D002265:Carboxylic Ester Hydrolases; C019262:galactolipase; D009584:Nitrogen