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The Arabidopsis sex1 Mutant Is Defective in the R1 Protein, a General Regulator of Starch Degradation in Plants, and Not in the Chloroplast Hexose Transporter

Tien-Shin Yu, Heike Kofler, Rainer E. Häusler, Diana Hille, Ulf-Ingo Flügge, Samuel C. Zeeman, Alison M. Smith, Jens Kossmann, James Lloyd, Gerhard Ritte, Martin Steup, Wei-Ling Lue, Jychian Chen and Andreas Weber
The Plant Cell
Vol. 13, No. 8 (Aug., 2001), pp. 1907-1918
DOI: 10.2307/3871327
Stable URL: http://www.jstor.org/stable/3871327
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Arabidopsis sex1 Mutant Is Defective in the R1 Protein, a General Regulator of Starch Degradation in Plants, and Not in the Chloroplast Hexose Transporter
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Abstract

Starch is the major storage carbohydrate in higher plants and of considerable importance for the human diet and for numerous technical applications. In addition, starch can be accumulated transiently in chloroplasts as a temporary deposit of carbohydrates during ongoing photosynthesis. This transitory starch has to be mobilized during the subsequent dark period. Mutants defective in starch mobilization are characterized by high starch contents in leaves after prolonged periods of darkness and therefore are termed starch excess (sex) mutants. Here we describe the molecular characterization of the Arabidopsis sex1 mutant that has been proposed to be defective in the export of glucose resulting from hydrolytic starch breakdown. The mutated gene in sex1 was cloned using a map-based cloning approach. By complementation of the mutant, immunological analysis, and of starch phosphorylation, we show that sex1 is defective in the Arabidopsis homolog of the R1 protein and not in the hexose transporter. We propose that the SEX1 protein (R1) functions as an overall regulator of starch mobilization by controlling the phosphate content of starch.

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