|Nahm, Back Hie|
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2004
Publication Date: 10/29/2004
Citation: Kim, W., Kim, J., Krishnan, H.B., Nahm, B. 2004. Expression of the escherichia coli branching enzyme in the caryopsis of transgenic rice results in increased branching of amylopectin. Planta. 220(5):689-695. Interpretive Summary: Despite a significant increase in food production during the last century, world production will need to be doubled or tripled by the year 2050 to meet the needs of an expected 10 billion global population. Rice is the staple food of the majority of 3.5 billion people in Asia. Increases in population in the rice growing regions of Asia will require 70% more rice in 2025 than is produced today. In addition, rice, in its milled form, is poor in essential amino acids and a range of vitamins and micronutrients, and that creates malnutrition. Transgenic approaches are being utilized to improve rice grain quality, including modification of starch, amino acids, micronutrients, and vitamins. In this study, we have modified the physiochemical properties of rice starch by genetic engineering. By expressing a branching enzyme from a bacterium, we have altered the chemical properties of rice starch. Such a modified starch will be a valuable resource to researchers in the food industry in their work to reduce malnutrition.
Technical Abstract: Physiochemical properties of starch are dependent on several factors, including the relative abundance of amylose and amylopectin, and the degree of amylopectin branching. Utilizing Agrobacterium-mediated transformation, a construct containing the coding region of the branching enzyme of Escherichia coli, under transcriptional control of the rice starch branching enzyme promoter, was introduced into rice cv. Nakdong. To enhance glgB expression, the rice starch branching enzyme first intron and matrix attachment region sequence (MAR) from chicken lysozyme were included in the expression vector. A total of 11 independent transgenic rice plants were generated. Southern blot analysis indicated that copy number of glgB integrated into transgenic rice varied from one to five. High-performance liquid chromatography analysis of starch from transgenic lines showed that amylopectin from the transgenic lines exhibited greater branching than that of non-transgenic rice. The A/B1 ratio in amylopectin increased from 1.3 to 2.3 and the total branching ratio, A+B1/B rest, increased from 6 to 12 in transgenic rice. The observed increase in the short-chain fractions having a degree of polymerization between 6 and 10 is expected to have a significant effect on retrogradation. Our study demonstrates that amylopectin branching can be altered in vivo, thus changing the physiochemical properties of starch.