title: The path to triacylglyceride obesity in the sta6 strain of Chlamydomonas reinhardtii.
abstract: When the sta6 (starch-null) strain of the green microalga Chlamydomonas reinhardtii is nitrogen starved in acetate and then "boosted" after 2 days with additional acetate, the cells become "obese" after 8 days, with triacylglyceride (TAG)-filled lipid bodies filling their cytoplasm and chloroplasts. To assess the transcriptional correlates of this response, the sta6 strain and the starch-forming cw15 strain were subjected to RNA-Seq analysis during the 2 days prior and 2 days after the boost, and the data were compared with published reports using other strains and growth conditions. During the 2 h after the boost, ∼425 genes are upregulated ≥2-fold and ∼875 genes are downregulated ≥2-fold in each strain. Expression of a small subset of "sensitive" genes, encoding enzymes involved in the glyoxylate and Calvin-Benson cycles, gluconeogenesis, and the pentose phosphate pathway, is responsive to culture conditions and genetic background as well as to boosting. Four genes-encoding a diacylglycerol acyltransferase (DGTT2), a glycerol-3-P dehydrogenase (GPD3), and two candidate lipases (Cre03.g155250 and Cre17.g735600)-are selectively upregulated in the sta6 strain. Although the bulk rate of acetate depletion from the medium is not boost enhanced, three candidate acetate permease-encoding genes in the GPR1/FUN34/YaaH superfamily are boost upregulated, and 13 of the "sensitive" genes are strongly responsive to the cell's acetate status. A cohort of 64 autophagy-related genes is downregulated by the boost. Our results indicate that the boost serves both to avert an autophagy program and to prolong the operation of key pathways that shuttle carbon from acetate into storage lipid, the combined outcome being enhanced TAG accumulation, notably in the sta6 strain.
authors.affiliation: Department of Biology, Washington University, St. Louis, Missouri, USA.
authors.forename: Ursula
authors.initials: U
authors.lastname: Goodenough
authors.forename: Ian
authors.initials: I
authors.lastname: Blaby
authors.forename: David
authors.initials: D
authors.lastname: Casero
authors.forename: Sean D
authors.initials: SD
authors.lastname: Gallaher
authors.forename: Carrie
authors.initials: C
authors.lastname: Goodson
authors.forename: Shannon
authors.initials: S
authors.lastname: Johnson
authors.forename: Jae-Hyeok
authors.initials: JH
authors.lastname: Lee
authors.forename: Sabeeha S
authors.initials: SS
authors.lastname: Merchant
authors.forename: Matteo
authors.initials: M
authors.lastname: Pellegrini
authors.forename: Robyn
authors.initials: R
authors.lastname: Roth
authors.forename: Jannette
authors.initials: J
authors.lastname: Rusch
authors.forename: Manmilan
authors.initials: M
authors.lastname: Singh
authors.forename: James G
authors.initials: JG
authors.lastname: Umen
authors.forename: Taylor L
authors.initials: TL
authors.lastname: Weiss
authors.forename: Tuya
authors.initials: T
authors.lastname: Wulan
mesh_terms: D000085:Acetates / Q000378:metabolism; D048429:Cell Size; D016825:Chlamydomonas reinhardtii / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D051048:Diacylglycerol O-Acyltransferase / Q000235:genetics / Q000378:metabolism; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000235:genetics* / Q000378:metabolism; D005993:Glycerolphosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D008049:Lipase / Q000235:genetics / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D017384:Sequence Deletion; D013213:Starch / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D000085:Acetates; D014280:Triglycerides; D013213:Starch; D005993:Glycerolphosphate Dehydrogenase; D051048:Diacylglycerol O-Acyltransferase; D051599:Glucose-1-Phosphate Adenylyltransferase; D008049:Lipase; D009584:Nitrogen