title: Regulation of synthesis and degradation of a sulfolipid under sulfur-starved conditions and its physiological significance in Chlamydomonas reinhardtii.
abstract: Regulation of synthesis and degradation of sulfoquinovosyl diacylglycerol (SQDG), one of the membrane lipids that construct thylakoids, under sulfur (S)-starved conditions and its physiological significance were explored in a green alga, Chlamydomonas reinhardtii. Here, we used sac1 and sac3 mutants defective in response to ambient S-status to characterize the system of known induction of SQDG degradation by S starvation that ensures a major S source for protein synthesis. The SQDG synthesis system was monitored in the wild type during S starvation. An SQDG-deficient mutant, hf-2, was utilized to discover functions where SQDG metabolism participates during S starvation. The induction of SQDG degradation was largely repressed in both sac1 and sac3 mutants. The SQDG synthesis capacity was increased by 40% after S starvation, with a sixfold elevation in the mRNA level of the SQD1 gene for SQDG synthesis. Compared with the wild type, hf-2 had decreased protein accumulation, photosystem (PS) I stability and growth rate. A role of SQDG as an S storage lipid is fulfilled under the control of both SAC1 and SAC3 genes, and it is essential for proper protein synthesis in acclimatization of cells to S starvation. The enhancement in SQDG synthesis may reflect the importance of SQDG as the membrane lipid that stabilizes the PSI complex.
authors.affiliation: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Sugimoto
authors.forename: Mikio
authors.initials: M
authors.lastname: Tsuzuki
authors.forename: Norihiro
authors.initials: N
authors.lastname: Sato
mesh_terms: D001192:Arylsulfatases / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000502:physiology*; D006017:Glycolipids / Q000096:biosynthesis*; D008055:Lipids / Q000096:biosynthesis*; D009154:Mutation / Q000235:genetics; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013455:Sulfur / Q000172:deficiency* / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D006017:Glycolipids; D008055:Lipids; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; C015518:sulfolipids; C013694:sulfoquinovosyl diglyceride; D013455:Sulfur; D001192:Arylsulfatases; D012273:Ribulose-Bisphosphate Carboxylase