Professor, Institute of Science and Technology, Niigata University, Niigata, Japan

Biograph
Dr. Kimiko Itoh was awarded Ph. D in field of plant molecular biology at Toho University, Japan, in 1994. She started her career in PlanTech Research Institute, Mitsubishi Chemical Corporation, Yokohama, Japan and she was engaged in molecular biological studies of rice and Brassica genomes, development of disease resistant and insect resistant transgenic rice, and DH lines of oil seed rape, for 10 years, then she moved to Niigata University. Currently, she is professor of Institute of Science and Technology, Niigata University and is engaged in education at Faculty of Agriculture, College of Creative studies, and Graduate School of Science and Technology. She also involved in the establishment of Support Office for Female Researcher (currently Office of Equality and Diversity) and implement the support project for 5 years as the initial member. Her major is Applied Glycoscience and Plant Science and her research group currently focused on development of alpha-glucan (starch and bacterial glycogen) with novel structure and properties, molecular mechanisms of abiotic stress responses in rice and omics analysis of microorganism’s volatile compound promoted high yielding rice.

Speech Title: Development of Super-high amylose starch

Abstract: Super-high amylose starch contains much amount of resistant starch with features kind of soluble dietary fiber in human gut, and can have human health benefit. Super-high amylose starches have been developed in maize and barley, and these starches contain over 60% amylose in a weight ratio and much amount of longer glucose unit-chains in amylopectin molecule. Such the long glucose unit-chains are caused by reduced activity of starch branching enzymes, which catalyses formation of alpha-1,6-bond of glucose chain, and generates a side chains of amylopectin.

Rice starch branching enzyme has three isoforms, BEI, BEIIa, and BEIIIa. Suppression of those isoforms’ expression led to remarkable increase in amylose contents, and the starch contains over 60% apparent amylose, that is super-high amylose starch. We measured amount of the resistant starch by enzyme digestion method, and results showed that amount of resistant starch in the super-high amylose starch is extremely higher than that of normal rice starch. We analysed the macro-structure of the starch grain by using electron probe microanalyzer, and revealed small and round structure of super-high amylose starch grains. The characteristic macro-structure thought to be a cause of floury texture of the rice seeds. We also analysed micro-structure of the super-high amylose starch by high performance size-exclusive column chromatography method, and the result indicated that the super-high amylose rice starch contains very low amount of amylopectin, and the disturbance of the unit chain of amylopectin was extremely abnormal, no peak in the profile. From these results, we discuss the mechanisms of formation of the super-high amylose starch, and resistant starch.

Keywords: Rice; super- high amylose starch; Starch Branching Enzyme; Resistant starch

Acknowledgements: We thank to Dr Sawamura for providing vector. This work is supported by the KAKENHI Grants-in-Aid for Scientific Research (C) (15K00779) from Japan Society for the Promotion of Sciences.