Poster: Integrated Plant Biology

Abs # 91: Use of Synechocystis sp. Strain PCC 6803 as a model system to study starch granule development

Presenter:	Pieris, Shayani D.N., shayani@iastate.edu
Authors	Pieris, Shayani D.N. (A)   Spalding, Martin H (A)   Jane, Jay-lin  (A)
Affiliations:	(A): Iowa State University

Starch is the most important carbohydrate reserve in plants and consists of two components, amylose (Am) and amylopectin (Ap). Am makes up 20-30 % of starch and is made of á-(1,4) linked glucose units resulting in an essentially linear molecule, and Ap makes up 70-80 % of starch and is also made up of glucose units linked by á-(1,4) bonds in the linear portions with á-(1,6) bonds at the branch points. Though the enzymes involved in starch biosynthesis are well studied, factors that control the structure of Ap, which is responsible for the semi-crystalline nature of starch, are not well understood. The hypothesis that we are following is that cluster-branching pattern and bimodal distribution of branch chains, along with the lipid rich nucleating environment of the thylakoid membranes are sufficient for granule initiation and development. Synechocystis sp. Strain PCC 6803 is a cyanobacterium that we are using as a model system to study granule development. We have generated mutants of Synechocystis expressing maize starch branching enzyme I (SBE I), which is known to transfer longer chains than glycogen branching enzyme (GBE), in a wild type (WT) background as well as in a mutant background lacking glycogen branching enzyme (GBE). Mutants expressing maize SBE I have been produced and segregated in both backgrounds. Initial experiments on the glucan extracted from the transgenic mutants expressing maize SBE I in each background showed the presence of a molecule larger than that present in the recipient strain. Further characterization of these transgenic mutants and the glucans they produce will be discussed.