Waxy Chlamydomonas reinhardtii: monocellular algal mutants defective in amylose biosynthesis and granule-bound starch synthase activity accumulate a structurally modified amylopectin.
Amylose-defective mutants were selected after UV mutagenesis of Chlamydomonas reinhardtii cells. Two recessive nuclear alleles of the ST-2 gene led to the disappearance not only of amylose but also of a fraction of the amylopectin. Granule-bound starch synthase activities were markedly reduced in strains carrying either st-2-1 or st-2-2, as is the case for amylose-deficient (waxy) endosperm mutants of higher plants. The main 76-kDa protein associated with the starch granule was either missing or greatly diminished in both mutants, while st-2-1-carrying strains displayed a novel 56-kDa major protein. Methylation and nuclear magnetic resonance analysis of wild-type algal storage polysaccharide revealed a structure identical to that of higher-plant starch, while amylose-defective mutants retained a modified amylopectin fraction. We thus propose that the waxy gene product conditions not only the synthesis of amylose from endosperm storage tissue in higher-plant amyloplasts but also that of amylose and a fraction of amylopectin in all starch-accumulating plastids. The nature of the ST-2 (waxy) gene product with respect to the granule-bound starch synthase activities is discussed.
Delrue
B
B
Laboratoire de Chimie Biologique, Université des Sciences et Techniques de Lille Flandres-Artois 59655, Villeneuve d'Ascq, France.
Fontaine
T
T
Routier
F
F
Decq
A
A
Wieruszeski
J M
JM
Van Den Koornhuyse
N
N
Maddelein
M L
ML
Fournet
B
B
Ball
S
S
D000483:Alleles; D000687:Amylopectin / Q000235:genetics* / Q000378:metabolism; D000688:Amylose / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D009154:Mutation; D012641:Selection, Genetic; D013213:Starch / Q000737:chemistry; D013214:Starch Synthase / Q000235:genetics*
D013213:Starch; D000688:Amylose; D000687:Amylopectin; D013214:Starch Synthase