Journal Article

An extra-plastidial α-glucan, water dikinase from <i>Arabidopsis</i> phosphorylates amylopectin <i>in vitro</i> and is not necessary for transient starch degradation

Mikkel A. Glaring, Agnieszka Zygadlo, David Thorneycroft, Alexander Schulz, Steven M. Smith, Andreas Blennow and Lone Baunsgaard

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 58, issue 14, pages 3949-3960
Published in print November 2007 | ISSN: 0022-0957
Published online November 2007 | e-ISSN: 1460-2431 | DOI:

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Starch phosphorylation catalysed by the α-glucan, water dikinases (GWD) has profound effects on starch degradation in plants. The Arabidopsis thaliana genome encodes three isoforms of GWD, two of which are localized in the chloroplast and are involved in the degradation of transient starch. The third isoform, termed AtGWD2 (At4g24450), was heterologously expressed and purified and shown to have a substrate preference similar to potato GWD. Analyses of AtGWD2 null mutants did not reveal any differences in growth or starch and sugar levels, when compared to the wild type. Subcellular localization studies in Arabidopsis leaves and in vitro chloroplast import assays indicated that AtGWD2 was not targeted to the chloroplasts. The AtGWD2 promoter showed a highly restricted pattern of activity, both spatially and temporally. High activity was observed in the companion cells of the phloem, with expression appearing just before the onset of senescence. Taken together, these data indicate that, although AtGWD2 is capable of phosphorylating α-glucans in vitro, it is not directly involved in transient starch degradation.

Keywords: Arabidopsis; dikinase; GWD; phloem; starch degradation; starch phosphorylation

Journal Article.  7631 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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