Submitted to: Maize Genetics Conference Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/11/1999
Publication Date: N/A
Technical Abstract: This study investigated the relationship between the starch branching enzymes of maize and glucan synthases using the yeast Saccharomyces cerevisiae as a model system. Yeast produces glycogen as a glucose storage molecule, whereas maize produces starch, however, both compounds are produced by the combined action of glucan synthases (GS) and glucan branching enzymes (BE). Yeast strains with glc3 mutations and thus lacking BE fail to accumulate glycogen and stain yellow with iodine vapor. This suggests that BE is required for normal glycogen synthesis and possibly for GS activity. We demonstrate that GS protein accumulates normally in a glc3deletion strain, indicating that BE does not negatively affect GS gene expression or protein stability. Maize BEIIb was expressed in the glc3- yeast and resulted in the production of a glucan with properties intermediate to glycogen and the amylopectin produced in maize endosperm. Maize BEIIb is therefore active in yeast and is able to provide the essential function required for GS activity. Coexpression of maize BEI and BEIIb in the glc3 -yeast strain resulted in the production of a different glucan structure with properties resembling those of maize amylopectin, thus demonstrating BEI activity in yeast. Expression of maize BEI by itself, however, did not result in the production of a branched glucan. These results establish a powerful system for probing the relationship between starch branching enzymes and glucan synthases, which is likely to be a critical factor in determining starch structure in maize endosperm.