title: Circadian clock regulation of starch metabolism establishes GBSSI as a major contributor to amylopectin synthesis in Chlamydomonas reinhardtii.
abstract: Chlamydomonas reinhardtii displays a diurnal rhythm of starch content that peaks in the middle of the night phase if the algae are provided with acetate and CO(2) as a carbon source. We show that this rhythm is controlled by the circadian clock and is tightly correlated to ADP-glucose pyrophosphorylase activity. Persistence of this rhythm depends on the presence of either soluble starch synthase III or granule-bound starch synthase I (GBSSI). We show that both enzymes play a similar function in synthesizing the long glucan fraction that interconnects the amylopectin clusters. We demonstrate that in log phase-oscillating cultures, GBSSI is required to obtain maximal polysaccharide content and fully compensates for the loss of soluble starch synthase III. A point mutation in the GBSSI gene that prevents extension of amylopectin chains, but retains the enzyme's normal ability to extend maltooligosaccharides, abolishes the function of GBSSI both in amylopectin and amylose synthesis and leads to a decrease in starch content in oscillating cultures. We propose that GBSSI has evolved as a major enzyme of amylopectin synthesis and that amylose synthesis comes as a secondary consequence of prolonged synthesis by GBSSI in arrhythmic systems. Maintenance in higher plant leaves of circadian clock control of GBSSI transcription is discussed.
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, Unité Mixte de Recherche 8576, Centre National de la Recherche Scientifique, Université des Sciences et Technologies de Lille, Institut Fédératif de Recherche, 59655 Villeneuve d'Ascq cedex, France.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Ral
authors.forename: Christophe
authors.initials: C
authors.lastname: Colleoni
authors.forename: Fabrice
authors.initials: F
authors.lastname: Wattebled
authors.forename: David
authors.initials: D
authors.lastname: Dauvillée
authors.forename: Clément
authors.initials: C
authors.lastname: Nempont
authors.forename: Philippe
authors.initials: P
authors.lastname: Deschamps
authors.forename: Zhongyi
authors.initials: Z
authors.lastname: Li
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Morell
authors.forename: Ravindra
authors.initials: R
authors.lastname: Chibbar
authors.forename: Saul
authors.initials: S
authors.lastname: Purton
authors.forename: Christophe
authors.initials: C
authors.lastname: d'Hulst
authors.forename: Steven G
authors.initials: SG
authors.lastname: Ball
mesh_terms: D000687:Amylopectin / Q000096:biosynthesis*; D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D017125:Genes, Protozoan; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D013214:Starch Synthase / Q000378:metabolism*
chemical_list: D000687:Amylopectin; D005964:Glucosyltransferases; C434607:granule-bound starch synthase I; D013214:Starch Synthase; D051599:Glucose-1-Phosphate Adenylyltransferase