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Evidence for distinct mechanisms of starch granule breakdown in plants
Citation
Delatte, T and Umhang, M and Trevisan, M and Eicke, S and Thorneycroft, D and Smith, SM and Zeeman, SC, Evidence for distinct mechanisms of starch granule breakdown in plants, Journal of Biological Chemistry, 281, (17) pp. 12050-12059. ISSN 0021-9258 (2006) [Refereed Article]
Copyright Statement
© 2006 by The American Society for Biochemistry and Molecular Biology
DOI: doi:10.1074/jbc.M513661200
Abstract
The aim of this work was to understand the initial steps of starch breakdown inside chloroplasts. In the non-living endosperm
of germinating cereal grains, starch breakdown is initiated by α-amylase secreted from surrounding cells. However, loss of
α-amylase from Arabidopsis does not prevent chloroplastic starch breakdown (Yu, T.-S., Zeeman, S. C., Thorneycroft, D., Fulton, D. C., Dunstan, H.,
Lue, W.-L., Hegemann, B., Tung, S.-Y., Umemoto, T., Chapple, A., Tsai, D.-L., Wang, S.-M, Smith, A. M., Chen, J., and Smith,
S. M. (2005) J. Biol. Chem. 280, 9773-9779), implying that other enzymes must attack the starch granule. Here, we present evidence that the debranching
enzyme isoamylase 3 (ISA3) acts at the surface of the starch granule. Atisa3 mutants have more leaf starch and a slower rate of starch breakdown than wild-type plants. The amylopectin of Atisa3 contains many very short branches and ISA3-GFP localizes to granule-like structures inside chloroplasts. We suggest that
ISA3 removes short branches from the granule surface. To understand how some starch is still degraded in Atisa3 mutants we eliminated a second debranching enzyme, limit dextrinase (pullulanase-type). Atlda mutants are indistinguishable from the wild type. However, the Atisa3/Atlda double mutant has a more severe starch-excess phenotype and a slower rate of starch breakdown than Atisa3 single mutants. The double mutant accumulates soluble branched oligosaccharides (limit dextrins) that are undetectable in
the wild-type and the single mutants. Together these results suggest that glucan debranching occurs primarily at the granule
surface via ISA3, but in its absence soluble branched glucans are debranched in the stroma via limit dextrinase. Consistent
with this model, chloroplastic α-amylase AtAMY3, which could release soluble branched glucans, is induced in Atisa3 and in the Atisa3/Atlda double mutant.
Item Details
Item Type: | Refereed Article |
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Keywords: | starch catabolism, debranching enzyme isoamylase 3, ISA3 |
Research Division: | Biological Sciences |
Research Group: | Plant biology |
Research Field: | Plant physiology |
Objective Division: | Expanding Knowledge |
Objective Group: | Expanding knowledge |
Objective Field: | Expanding knowledge in the biological sciences |
UTAS Author: | Smith, SM (Professor Steven Smith) |
ID Code: | 101516 |
Year Published: | 2006 |
Web of Science® Times Cited: | 114 |
Deposited By: | Plant Science |
Deposited On: | 2015-06-25 |
Last Modified: | 2015-09-25 |
Downloads: | 0 |
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