Genetic modification of cornstarch structure and functionality with barley starch biosynthetic enzymes.

NOVEMBER 5-9, 2000 KANSAS CITY, MISSOURI

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Genetic modification of cornstarch structure and functionality with barley starch biosynthetic enzymes. B. MOU (1), S. Yoo (1), B. Seo (2), C. Jansson (3), M. James (2), and J. Jane (1). (1) Dept. of Food Science & Human Nutrition; (2) Dept. of Biochemistry and Biophysics, Iowa State University, Ames, IA 50011; (3) Dept. of Biochemistry, Stockholm University, S-106 91 Stockholm, Sweden.

To modify the structure and improve the functionality of cornstarch, we attempt to transform maize plants with starch biosynthetic enzyme genes from barley. Expression vector pMO12 containing barley starch branching enzyme (SBEIIa) full-length cDNA and a 6x-histidine tag was constructed. The construct has been introduced into maize callus tissue from Oh43 inbred line by particle bombardment. To test the function of the barley SBEIIa clone and the effect of tags on enzyme activity, SBEIIa cDNAs with and without the histidine tag were cloned into yeast pYX vector to transform a yeast mutant strain lacking branching enzyme activity (glc3-). The barley SBEIIa gene complemented the yeast branching enzyme activity. However, the complementation efficiency was lower for the SBEIIa with histidine tag (12 out of 25 tests were positive or 48%) than the one without the tag (10/12 or 83%). PCR analyses showed that those non-complementing yeast cells do not contain the SBEIIa gene. Glycogens from the wild type and complemented yeast strains have been isolated and their structures were analyzed. The molecular weight was 4.31+-0.23 × 10(^7) for the glucan from wild type yeast and 2.46 + -0.18 × 10(^7) for the one from complemented yeast strain.