Further Evidence for the Mandatory Nature of Polysaccharide Debranching for the Aggregation of Semicrystalline Starch and for Overlapping Functions of Debranching Enzymes in Arabidopsis Leaves
- 24 September 2008
- journal article
- research article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 148 (3), 1309-1323
- https://doi.org/10.1104/pp.108.129379
Abstract
Four isoforms of debranching enzymes are found in the genome of Arabidopsis (Arabidopsis thaliana): three isoamylases (ISA1, ISA2, and ISA3) and a pullulanase (PU1). Each isoform has a specific function in the starch pathway: synthesis and/or degradation. In this work we have determined the levels of functional redundancy existing between these isoforms by producing and analyzing different combinations of mutations: isa3-1 pu1-1, isa1-1 isa3-1, and isa1-1 isa3-1 pu1-1. While the starch content strongly increased in the isa3-1 pu1-1 double mutant, the latter decreased by over 98% in the isa1-1 isa3-1 genotype and almost vanished in triple mutant combination. In addition, whereas the isa3-1 pu1-1 double mutant synthesizes starch very similar to that of the wild type, the structure of the residual starch present either in isa1-1 isa3-1 or in isa1-1 isa3-1 pu1-1 combination is deeply affected. In the same way, water-soluble polysaccharides that accumulate in the isa1-1 isa3-1 and isa1-1 isa3-1 pu1-1 genotypes display strongly modified structure compared to those found in isa1-1. Taken together, these results show that in addition to its established function in polysaccharide degradation, the activity of ISA3 is partially redundant to that of ISA1 for starch synthesis. Our results also reveal the dual function of pullulanase since it is partially redundant to ISA3 for degradation and to ISA1 for synthesis. Finally, x-ray diffraction analyses suggest that the crystallinity and the presence of the 9- to 10-nm repetition pattern in starch precisely depend on the level of debranching enzyme activity.Keywords
This publication has 36 references indexed in Scilit:
- Glucan, water dikinase phosphorylates crystalline maltodextrins and thereby initiates solubilizationThe Plant Journal, 2008
- β-AMYLASE4, a Noncatalytic Protein Required for Starch Breakdown, Acts Upstream of Three Active β-Amylases in Arabidopsis ChloroplastsPlant Cell, 2008
- Starch Biosynthetic Enzymes from Developing Maize Endosperm Associate in Multisubunit ComplexesPlant Physiology, 2008
- Analysis of Protein Complexes in Wheat Amyloplasts Reveals Functional Interactions among Starch Biosynthetic EnzymesPlant Physiology, 2008
- Glucan, Water Dikinase Activity Stimulates Breakdown of Starch Granules by Plastidial β-AmylasesPlant Physiology, 2007
- The phenotype of soluble starch synthase IV defective mutants of Arabidopsis thaliana suggests a novel function of elongation enzymes in the control of starch granule formationThe Plant Journal, 2007
- Soluble starch synthase I: a major determinant for the synthesis of amylopectin in Arabidopsis thaliana leavesThe Plant Journal, 2005
- Diurnal Changes in the Transcriptome Encoding Enzymes of Starch Metabolism Provide Evidence for Both Transcriptional and Posttranscriptional Regulation of Starch Metabolism in Arabidopsis LeavesPlant Physiology, 2004
- Genome-Wide Insertional Mutagenesis of Arabidopsis thalianaScience, 2003
- Novel, Starch-Like Polysaccharides Are Synthesized by an Unbound Form of Granule-Bound Starch Synthase in Glycogen-Accumulating Mutants ofChlamydomonas reinhardtiiPlant Physiology, 1999