THE PATHWAY OF CYTOSOLIC STARCH SYNTHESIS IN THE MODEL GLAUCOPHYTE CYANOPHORA PARADOXA.

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Plancke, Charlotte | Colleoni, Christophe | Deschamps, Philippe | Dauvillée, David | Nakamura, Yasunori | Haebel, Sophie | Ritte, Gehrardt | Steup, Martin | Buléon, Alain | Putaux, Jean-Luc | Dupeyre, Danielle | d'Hulst, Christophe | Ral, Jean-Philippe | Loffelhardt, Wolfgang | Ball, Steven G

Edité par CCSD ; American Society for Microbiology -

The nature of the cytoplasmic pathway of starch biosynthesis was investigated in the model glaucophyte Cyanophora paradoxa. The storage polysaccharide granules are shown to be composed of both amylose and amylopectin fractions with a chain length distribution and crystalline organization similar to those of green algae and land plant starch. Preliminary characterization of the starch pathway demonstrates that Cyanophora paradoxa contains several UDP-glucose utilising soluble starch synthase activities related to those of the rhodophyceae. In addition Cyanophora paradoxa synthesizes amylose with a granule-bound starch synthase displaying a preference for UDP-glucose. A debranching enzyme of isoamylase specificity and multiple starch phosphorylases are also evidenced in the model glaucophyte. The picture emerging from our biochemical and molecular characterizations consists of the presence of an UDP-glucose-based pathway similar to that recently proposed for the red algae, the cryptophytes and the alveolates. The correlative presence of isoamylase and starch among photosynthetic eukaryotes is discussed.

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