Present address: DIREVO Biotech AG, Nattermannallee 1, D-50829 Cologne, Germany.
Downregulation of a chloroplast-targeted β-amylase leads to a starch-excess phenotype in leaves
Article first published online: 30 MAY 2002
The Plant Journal
Volume 30, Issue 5, pages 581–591, June 2002
How to Cite
Scheidig, A., Fröhlich, A., Schulze, S., Lloyd, J. R. and Kossmann, J. (2002), Downregulation of a chloroplast-targeted β-amylase leads to a starch-excess phenotype in leaves. The Plant Journal, 30: 581–591. doi: 10.1046/j.1365-313X.2002.01317.x
- Issue published online: 30 MAY 2002
- Article first published online: 30 MAY 2002
- Received 24 January 2002; revised 28 February 2002; accepted 8 March 2002.
- starch degradation;
- transitory starch;
- plastid localization;
A functional screen in Escherichia coli was established to identify potato genes coding for proteins involved in transitory starch degradation. One clone isolated had a sequence very similar to a recently described chloroplast-targeted β-amylase of Arabidopsis. Expression of the gene in E. coli showed that the protein product was a functional β-amylase that could degrade both starch granules and solubilized amylopectin, while import experiments demonstrated that the β-amylase was imported and processed into pea chloroplasts. To study the function of the protein in transitory starch degradation, transgenic potato plants were generated where its activity was reduced using antisense techniques. Analysis of plants reduced in the presence of this β-amylase isoform showed that their leaves had a starch-excess phenotype, indicating a defect in starch degradation. In addition, it was shown that the antisense plants degraded only 8–30% of their total starch, in comparison with 50% in the wild type, over the dark period. This is the first time that a physiological role for a β-amylase in plants has been demonstrated.