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Starch synthesis in potato tubers is regulated by post-translational redox modification of ADP-glucose pyrophosphorylase: a novel regulatory mechanism linking starch synthesis to the sucrose supply.
- Source :
-
The Plant cell [Plant Cell] 2002 Sep; Vol. 14 (9), pp. 2191-213. - Publication Year :
- 2002
-
Abstract
- Transcriptional and allosteric regulation of ADP-Glc pyrophosphorylase (AGPase) plays a major role in the regulation of starch synthesis. Analysis of the response after detachment of growing potato tubers from the mother plant revealed that this concept requires extension. Starch synthesis was inhibited within 24 h of tuber detachment, even though the catalytic subunit of AGPase (AGPB) and overall AGPase activity remained high, the substrates ATP and Glc-1-P increased, and the glycerate-3-phosphate/inorganic orthophosphate (the allosteric activator and inhibitor, respectively) ratio increased. This inhibition was abolished in transformants in which a bacterial AGPase replaced the potato AGPase. Measurements of the subcellular levels of each metabolite between Suc and starch established AGPase as the only step whose substrates increase and mass action ratio decreases after detachment of wild-type tubers. Separation of extracts on nonreducing SDS gels revealed that AGPB is present as a mixture of monomers and dimers in growing tubers and becomes dimerized completely in detached tubers. Dimerization led to inactivation of the enzyme as a result of a marked decrease of the substrate affinity and sensitivity to allosteric effectors. Dimerization could be reversed and AGPase reactivated in vitro by incubating extracts with DTT. Incubation of tuber slices with DTT or high Suc levels reduced dimerization, increased AGPase activation, and stimulated starch synthesis in vivo. In intact tubers, the Suc content correlated strongly with AGPase activation across a range of treatments, including tuber detachment, aging of the mother plant, heterologous overexpression of Suc phosphorylase, and antisense inhibition of endogenous AGPase activity. Furthermore, activation of AGPase resulted in a stimulation of starch synthesis and decreased levels of glycolytic intermediates.
- Subjects :
- Chloroplasts metabolism
Cytosol metabolism
Dithiothreitol pharmacology
Gene Expression Regulation, Enzymologic
Gene Expression Regulation, Plant
Glucose-1-Phosphate Adenylyltransferase
Glucosyltransferases genetics
Glucosyltransferases metabolism
Glyceraldehyde 3-Phosphate metabolism
Kinetics
Models, Biological
Nucleotidyltransferases drug effects
Nucleotidyltransferases genetics
Oxidation-Reduction
Phosphates metabolism
Plant Stems genetics
Plant Stems metabolism
Plants, Genetically Modified
Protein Processing, Post-Translational
Solanum tuberosum genetics
Solanum tuberosum metabolism
Vacuoles metabolism
Nucleotidyltransferases metabolism
Plant Stems enzymology
Solanum tuberosum enzymology
Starch biosynthesis
Sucrose metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 1040-4651
- Volume :
- 14
- Issue :
- 9
- Database :
- MEDLINE
- Journal :
- The Plant cell
- Publication Type :
- Academic Journal
- Accession number :
- 12215515
- Full Text :
- https://doi.org/10.1105/tpc.003640