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Expression of an engineered granule‐bound E scherichia coli glycogen branching enzyme in potato results in severe morphological changes in starch granules

2012; Wiley; Volume: 11; Issue: 4 Linguagem: Inglês

10.1111/pbi.12033

1467-7652

Xing‐Feng Huang, Farhad Nazarian‐Firouzabadi, Jean‐Paul Vincken, Qin Ji, Luc C. J. M. Suurs, Richard G. F. Visser, Luisa M. Trindade,

Potato Plant Research

Summary The E scherichia coli glycogen branching enzyme ( GLGB ) was fused to either the C ‐ or N ‐terminus of a starch‐binding domain ( SBD ) and expressed in two potato genetic backgrounds: the amylose‐free mutant ( amf ) and an amylose‐containing line ( K ardal). Regardless of background or construct used, a large amount of GLGB / SBD fusion protein was accumulated inside the starch granules, however, without an increase in branching. The presence of GLGB / SBD fusion proteins resulted in altered morphology of the starch granules in both genetic backgrounds. In the amf genetic background, the starch granules showed both amalgamated granules and porous starch granules, whereas in K ardal background, the starch granules showed an irregular rough surface. The altered starch granules in both amf and Kardal backgrounds were visible from the initial stage of potato tuber development. High‐throughput transcriptomic analysis showed that expression of GLGB / SBD fusion protein in potato tubers did not affect the expression level of most genes directly involved in the starch biosynthesis except for the up‐regulation of a beta‐amylase gene in K ardal background. The beta‐amylase protein could be responsible for the degradation of the extra branches potentially introduced by GLGB .