A novel isoform of glucan, water dikinase phosphorylates pre-phosphorylated α-glucans and is involved in starch degradation in Arabidopsis
Article first published online: 11 JAN 2005
The Plant Journal
Volume 41, Issue 4, pages 595–605, February 2005
How to Cite
Baunsgaard, L., Lütken, H., Mikkelsen, R., Glaring, M. A., Pham, T. T. and Blennow, A. (2005), A novel isoform of glucan, water dikinase phosphorylates pre-phosphorylated α-glucans and is involved in starch degradation in Arabidopsis. The Plant Journal, 41: 595–605. doi: 10.1111/j.1365-313X.2004.02322.x
- Issue published online: 11 JAN 2005
- Article first published online: 11 JAN 2005
- Received 22 September 2004; revised 12 November 2004; accepted 23 November 2004.
- starch degradation;
- starch phosphorylation;
An Arabidopsis thaliana gene encoding a homologue of the potato α-glucan, water dikinase GWD, previously known as R1, was identified by screening the Arabidopsis genome and named AtGWD3. The AtGWD3 cDNA was isolated, heterologously expressed and the protein was purified to apparent homogeneity to determine the enzymatic function. In contrast to the potato GWD protein, the AtGWD3 primarily catalysed phosphorylation at the C-3 position of the glucose unit of preferably pre-phosphorylated amylopectin substrate with long side chains. An Arabidopsis mutant, termed Atgwd3, with downregulated expression of the AtGWD3 gene was analysed. In Atgwd3 the amount of leaf starch was constantly higher than wild type during the diurnal cycle. Compared with wild-type leaf starch, the level of C-3 phosphorylation of the glucosyl moiety of starch in this mutant was reduced. Taken together, these data indicate that the C-3 linked phospho-ester in starch plays a so far unnoticed specific role in the degradation of transitory starch.