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Distinct Functions of STARCH SYNTHASE 4 Domains in Starch Granule Formation.

  • Lu KJ Department of Biology, ETH Zurich, 8092 Zurich, Switzerland.
  • Pfister B Department of Biology, ETH Zurich, 8092 Zurich, Switzerland.
  • Jenny C Department of Biology, ETH Zurich, 8092 Zurich, Switzerland.
  • Eicke S Department of Biology, ETH Zurich, 8092 Zurich, Switzerland.
  • Zeeman SC Department of Biology, ETH Zurich, 8092 Zurich, Switzerland szeeman@ethz.ch.
  • 2017-11-15
Published in:
  • Plant physiology. - 2018
Agrobacterium tumefaciens
Arabidopsis
Arabidopsis Proteins
Chloroplasts
Cytoplasmic Granules
Germination
Glycogen Synthase
Phenotype
Plant Development
Plant Leaves
Plants, Genetically Modified
Protein Domains
Starch
Starch Synthase
English The formation of normal starch granules in Arabidopsis (Arabidopsis thaliana) leaf chloroplasts requires STARCH SYNTHASE 4 (SS4). In plants lacking SS4, chloroplasts typically produce only one round granule rather than multiple lenticular granules. The mechanisms by which SS4 determines granule number and morphology are not understood. The N-terminal region of SS4 is unique among SS isoforms and contains several long coiled-coil motifs, typically implicated in protein-protein interactions. The C-terminal region contains the catalytic glucosyltransferase domains, which are widely conserved in plant SS and bacterial glycogen synthase (GS) isoforms. We investigated the specific roles of the N- and C-terminal regions of SS4 by expressing truncated versions of SS4 and a fusion between the N-terminal region of SS4 and GS in the Arabidopsis ss4 mutant. Expression of the N-terminal region of SS4 alone did not alter the ss4 mutant phenotype. Expression of the C-terminal region of SS4 alone increased granule initiation but did not rescue their aberrant round morphology. Expression of a self-priming GS from Agrobacterium tumefaciens also increased the number of round granules. Remarkably, fusion of the N-terminal region of SS4 to A. tumefaciens GS restored the development of wild-type-like lenticular starch granules. Interestingly, the N-terminal region of SS4 alone or when fused to GS conferred a patchy subchloroplastic localization similar to that of the full-length SS4 protein. Considered together, these data suggest that, while the glucosyltransferase activity of SS4 is important for granule initiation, the N-terminal part of SS4 serves to establish the correct granule morphology by properly localizing this activity.
Language
  • English
Open access status
bronze
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https://sonar.ch/global/documents/283419
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