Control of starch composition and structure through substrate supply in the monocellular alga Chlamydomonas reinhardtii.
In Chlamydomonas, as in higher plants, synthesis of ADP glucose catalyzed by ADP-glucose pyrophosphorylase is rate-limiting for the building of starch in the chloroplast. We have isolated disruptions of the STA1 ADP-glucose pyrophosphorylase structural gene that rendered the enzyme less responsive to the allosteric activator 3-phosphoglycerate. The structure and composition of the residual starch synthesized by all mutants of the STA1 locus is dramatically altered. The residual polysaccharide is shown to be devoid of amylose despite the presence of granule-bound starch synthase, the amylose biosynthetic enzyme. In addition, the fine structure of the mutant amylopectin revealed the presence of an altered chain-length distribution. This distribution mimicks that which is observed during growth and photosynthesis and differs markedly from that observed during storage. We therefore propose that low nucleotide sugar concentrations are either directly or indirectly responsible for the major differences observed in the composition or structure of starch during storage and photosynthesis.
Van den Koornhuyse
N
N
Laboratoire de Chimie Biologique, Unité Mixte de Recherche du CNRS 111, Université des Sciences et Techniques de Lille Flandres-Artois 59655 Villeneuve d'Ascq Cedex, France 59655.
Libessart
N
N
Delrue
B
B
Zabawinski
C
C
Decq
A
A
Iglesias
A
A
Carton
A
A
Preiss
J
J
Ball
S
S
D000687:Amylopectin / Q000302:isolation & purification / Q000378:metabolism; D000688:Amylose / Q000302:isolation & purification / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D003001:Cloning, Molecular; D017931:DNA Primers; D018744:DNA, Plant / Q000302:isolation & purification; D004171:Diploidy; D017343:Genes, Plant; D005838:Genotype; D051599:Glucose-1-Phosphate Adenylyltransferase; D006238:Haploidy; D007700:Kinetics; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009713:Nucleotidyltransferases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D013213:Starch / Q000096:biosynthesis* / Q000737:chemistry; D013214:Starch Synthase / Q000378:metabolism*; D014466:Ultraviolet Rays
D017931:DNA Primers; D018744:DNA, Plant; D013213:Starch; D000688:Amylose; D000687:Amylopectin; D013214:Starch Synthase; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase