Poster: Metabolic Engineering

Abs # 1008: An Arabidopsis gene encoding a plastid-targeted alpha-amylase

Presenter:	Chen, Jychian , mbjchen@ccvax.sinica.edu.tw
Authors	Chen, Jychian  (A)   Lue, Wei-Ling  (A)   Wang, Shue-Mei  (B)   Zeeman, Samuel  (C)
Affiliations:	(A): Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan (B): Botany Dept, National Taiwan University, Taiwan (C): Institute of Plant Sciences, University of Bern, Switzerland University of Bern,

An Arabidopsis gene (AtAMY1) encoding a novel, 93.5 kDa plastidial alpha-amylase was isolated and characterized. The C-terminal domain encoded by AtAMY1 is similar to other known extracellular alpha-amylases. However, the N-terminal domain shares similarity with the N-terminal region of the potato R1 protein, a protein that can bind to starch granules. We show that the AtAMY1 alpha-amylase is localized in chloroplasts and that the protein binds to transitory starch granules. We demonstrate that the mutant line sex4 of Arabidopsis, which has increased leaf starch content, has a reduced plastidial alpha-amylase activity, attributable to a decrease in AtAMY1 protein. As homologues of AtAMY1 have been identified in other species, it is inferred that this plastidial alpha-amylase may play roles in transitory starch degradation in plants. To study its role in starch degradation, we isolated one T-DNA insertion knockout Arabidopsis mutant of the AtAMY1 gene. Unexpectedly, transitory starch accumulated in leaves of this AtAMY1 knockout mutant was degraded in dark phase, similar to that of the wild type. This result suggests that other starch-degrading enzymes can break down transitory starch in the absence of AtAMY1 and the increase of leaf starch content in the sex4 mutant is not caused simply by deficiency of AtAMY1 protein.