title: Isolation and characterization of a mutant defective in triacylglycerol accumulation in nitrogen-starved Chlamydomonas reinhardtii.
abstract: Triacylglycerol (TAG), a major source of biodiesel production, accumulates in nitrogen-starved Chlamydomonas reinhardtii. However, the metabolic pathway of starch-to-TAG conversion remains elusive because an enzyme that affects the starch degradation is unknown. Here, we isolated a new class of mutant bgal1, which expressed an overaccumulation of starch granules and defective photosynthetic growth. The bgal1 was a null mutant of a previously uncharacterized β-galactosidase-like gene (Cre02.g119700), which decreased total β-galactosidase activity 40% of the wild type. Upon nitrogen starvation, the bgal1 mutant showed decreased TAG accumulation mainly due to the reduced flux of de novo TAG biosynthesis evidenced by increased unsaturation of fatty acid composition in TAG and reduced TAG accumulation by additional supplementation of acetate to the culture media. Metabolomic analysis of the bgal1 mutant showed significantly reduced levels of metabolites following the hydrolysis of starch and substrates for TAG accumulation, whereas metabolites in TCA cycle were unaffected. Upon nitrogen starvation, while levels of glucose 6-phosphate, fructose 6-phosphate and acetyl-CoA remained lower, most of the other metabolites in glycolysis were increased but those in the TCA cycle were decreased, supporting TAG accumulation. We suggest that BGAL1 may be involved in the degradation of starch, which affects TAG accumulation in nitrogen-starved C. reinhardtii. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, 128 sec.2 Academia Rd. Nankang, Taipei 11529, Taiwan. Electronic address: sunnyyaung@gate.sinica.edu.tw.
authors.forename: Chun-Hsien
authors.initials: CH
authors.lastname: Hung
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, 128 sec.2 Academia Rd. Nankang, Taipei 11529, Taiwan. Electronic address: kanehara@gate.sinica.edu.tw.
authors.forename: Kazue
authors.initials: K
authors.lastname: Kanehara
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, 128 sec.2 Academia Rd. Nankang, Taipei 11529, Taiwan; PRESTO, Japan Science and Technology Agency, A-1-8 Honcho Kawaguchi, Saitama, Japan. Electronic address: nakamura@gate.sinica.edu.tw.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakamura
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism; D020418:Algal Proteins / Q000235:genetics*; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism*; D005227:Fatty Acids / Q000096:biosynthesis* / Q000378:metabolism; D008055:Lipids / Q000096:biosynthesis / Q000235:genetics; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics; D018087:Plastids / Q000201:enzymology; D013213:Starch / Q000096:biosynthesis / Q000378:metabolism; D013217:Starvation; D014280:Triglycerides / Q000096:biosynthesis* / Q000235:genetics; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D005227:Fatty Acids; D008055:Lipids; D014280:Triglycerides; D000105:Acetyl Coenzyme A; D013213:Starch; D001616:beta-Galactosidase; D009584:Nitrogen
keywords: Chlamydomonas reinhardtii; Glycerolipid metabolism; Metabolomics; Nitrogen starvation; Triacylglycerol