Towards a more versatile alpha-glucan biosynthesis in plants

During the last 10 years, the increased need for starches with novel properties has occupied the research community, and many efforts were concentrated on unraveling the starch bio- synthesis pathways. The knowledge generated in these investigations was subsequently used to produce tailor-made starches in higher plants using recombinant DNA technology. Examples of starches with new functionalities are those with a modified degree of branching (Schwall et al. 2000, Shewma- ker et al. 1994, Kortstee et al. 1996) and the amylose-free starch (Visser et al. 1991a, Kuipers et al.1994), some of which hold potential for applications in the paper-, textile-, plastics-, food and pharmaceutical industry. The accumulation of more starch has also been an objective, but this will not be dis- cussed further here, (see: Slattery et al. 2000).
In our laboratory, we have embarked on two generic tech- nologies with a very wide range of applicability: (i) introduction of new linkages types and structural elements using glu- cansucrases, and (ii) engineering granule-boundness by using microbial starch-binding domains (SBDs). It is expected that these technologies will contribute substantially to the biosynthesis of more versatile α-glucans in the near future, leading to starches with altered functionalities that cannot be obtained by conventional breeding. In this study recent developments in starch modification using heterologous expression of microbial genes will be reviewed, with emphasis on the potato plant.