Engineering starch biosynthesis for increasing rice seed weight: the role of the cytoplasmic ADP-glucose pyrophosphorylase

ADP-glucose pyrophosphorylase (AGPase) controls a rate-limiting step in starch biosynthesis. In cereals, manipulation of this enzyme is a prime target to increase starch production during seed development as a means to increase sink strength and, in turn, crop yields. The Escherichia coli glgC tripl...

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Bibliographic Details
Published in:Plant science (Limerick) 2004-12, Vol.167 (6), p.1323-1333
Main Authors: Sakulsingharoj, Chotipa, Choi, Sang-Bong, Hwang, Seon-Kap, Edwards, Gerald E., Bork, Jennifer, Meyer, Christopher R., Preiss, Jack, Okita, Thomas W.
Format: Article
Language:English
Subjects:
ADP-glucose pyrophosphorylase
bacterial proteins
Biological and medical sciences
biosynthesis
cytoplasm
Cytoplasmic ADP-glucose pyrophosphorylase
Escherichia coli
Fundamental and applied biological sciences. Psychology
Germination and dormancy
glgc
molecular sequence data
nucleotide sequences
nucleotidyltransferases
Oryza sativa
Plant physiology and development
rice
Rice seed weight
seeds
starch
Starch biosynthesis
transgenes
transgenic plants
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Summary:ADP-glucose pyrophosphorylase (AGPase) controls a rate-limiting step in starch biosynthesis. In cereals, manipulation of this enzyme is a prime target to increase starch production during seed development as a means to increase sink strength and, in turn, crop yields. The Escherichia coli glgC triple mutant (TM) gene, which encodes a highly active and allosterically insensitive AGPase, was introduced into rice and expressed during endosperm development. The mutated enzyme was targeted to either the amyloplast or cytoplasm to determine the relationship between intracellular location of ADP-glucose formation and starch synthesis. Transgenic rice seeds expressing the amyloplast or cytoplasmic AGPase-TM showed up to 13-fold higher levels of AGPase activity compared to untransformed plants when assayed in the presence of inorganic phosphate to suppress the endogenous activity. Plants having elevated cytoplasmic AGPase activity under Pi-inhibitory conditions showed increases in 14C-sucrose labeling into starch and, in turn, increases (up to 11%) in seed weight over the wt. In contrast, transgenic plants expressing the amyloplast-targeted AGPase activity showed small to moderate increases in 14C-sucrose-labeling rates into starch and either a moderate increase in seed weight or, in several instances, a reduction in seed weight. Our results demonstrate that the intracellular location of AGPase has a marked effect on the capacity of the enzyme to increase starch synthesis and, in turn, seed weight.
ISSN:0168-9452
1873-2259
DOI:10.1016/j.plantsci.2004.06.028