Starch Granule Initiation in Arabidopsis Requires the Presence of Either Class IV or Class III Starch Synthases

The mechanisms underlying starch granule initiation remain unknown. We have recently reported that mutation of soluble starch synthase IV (SSIV) in Arabidopsis thaliana results in restriction of the number of starch granules to a single, large, particle per plastid, thereby defining an important com...

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Bibliographic Details
Published in:The Plant cell 2009-08, Vol.21 (8), p.2443-2457
Main Authors: Szydlowski, Nicolas, Ragel, Paula, Raynaud, Sandy, Lucas, M. Mercedes, Roldán, Isaac, Montero, Manuel, Muñoz, Francisco José, Ovecka, Miroslav, Bahaji, Abdellatif, Planchot, Véronique, Pozueta-Romero, Javier, D'Hulst, Christophe, Mérida, Ángel
Format: Article
Language:English
Subjects:
Arabidopsis - genetics
Arabidopsis - metabolism
Arabidopsis - ultrastructure
Arabidopsis Proteins - genetics
Arabidopsis Proteins - physiology
Biochemistry
Biochemistry, Molecular Biology
Biosynthesis
Chloroplasts
Enzymes
Glucans
Glycogen
Leaves
Life Sciences
Microscopy, Confocal
Microscopy, Electron, Transmission
Phenotypes
Plant cells
Plants
Plants, Genetically Modified - genetics
Plants, Genetically Modified - metabolism
Plants, Genetically Modified - ultrastructure
Plastids - genetics
Plastids - metabolism
Plastids - ultrastructure
Starch
Starch Synthase - genetics
Starch Synthase - physiology
Starches
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Summary:The mechanisms underlying starch granule initiation remain unknown. We have recently reported that mutation of soluble starch synthase IV (SSIV) in Arabidopsis thaliana results in restriction of the number of starch granules to a single, large, particle per plastid, thereby defining an important component of the starch priming machinery. In this work, we provide further evidence for the function of SSIV in the priming process of starch granule formation and show that SSIV is necessary and sufficient to establish the correct number of starch granules observed in wild-type chloroplasts. The role of SSIV in granule seeding can be replaced, in part, by the phylogenetically related SSIII. Indeed, the simultaneous elimination of both proteins prevents Arabidopsis from synthesizing starch, thus demonstrating that other starch synthases cannot support starch synthesis despite remaining enzymatically active. Herein, we describe the substrate specificity and kinetic properties of SSIV and its subchloroplastic localization in specific regions associated with the edges of starch granules. The data presented in this work point to a complex mechanism for starch granule formation and to the different abilities of SSIV and SSIII to support this process in Arabidopsis leaves.
ISSN:1040-4651
1532-298X
DOI:10.1105/tpc.109.066522