Plastidial phosphorylase is required for normal starch synthesis in Chlamydomonas reinhardtii.
Among the three distinct starch phosphorylase activities detected in Chlamydomonas reinhardtii, two distinct plastidial enzymes (PhoA and PhoB) are documented while a single extraplastidial form (PhoC) displays a higher affinity for glycogen as in vascular plants. The two plastidial phosphorylases are shown to function as homodimers containing two 91-kDa (PhoA) subunits and two 110-kDa (PhoB) subunits. Both lack the typical 80-amino-acid insertion found in the higher plant plastidial forms. PhoB is exquisitely sensitive to inhibition by ADP-glucose and has a low affinity for malto-oligosaccharides. PhoA is more similar to the higher plant plastidial phosphorylases: it is moderately sensitive to ADP-glucose inhibition and has a high affinity for unbranched malto-oligosaccharides. Molecular analysis establishes that STA4 encodes PhoB. Chlamydomonas reinhardtii strains carrying mutations at the STA4 locus display a significant decrease in amounts of starch during storage that correlates with the accumulation of abnormally shaped granules containing a modified amylopectin structure and a high amylose content. The wild-type phenotype could be rescued by reintroduction of the cloned wild-type genomic DNA, thereby demonstrating the involvement of phosphorylase in storage starch synthesis.
Dauvillée
David
D
Unité de Glycobiologie Structurale et Fonctionnelle, UMR8576 CNRS/USTL, IFR 118, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq, Cedex, France.
Chochois
Vincent
V
Steup
Martin
M
Haebel
Sophie
S
Eckermann
Nora
N
Ritte
Gerhard
G
Ral
Jean-Philippe
JP
Colleoni
Christophe
C
Hicks
Glenn
G
Wattebled
Fabrice
F
Deschamps
Philippe
P
d'Hulst
Christophe
C
Liénard
Luc
L
Cournac
Laurent
L
Putaux
Jean-Luc
JL
Dupeyre
Danielle
D
Ball
Steven G
SG
D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000687:Amylopectin / Q000737:chemistry / Q000378:metabolism; D000688:Amylose / Q000378:metabolism; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics; D005816:Genetic Complementation Test; D007527:Isoenzymes / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D006005:Phosphorylases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013213:Starch / Q000096:biosynthesis* / Q000648:ultrastructure
D020418:Algal Proteins; D007527:Isoenzymes; D013213:Starch; D000688:Amylose; D000687:Amylopectin; D006005:Phosphorylases; D009584:Nitrogen