Characterization and Utilization of Spontaneous Deficiency in Starch Branching Enzyme I of Rice (Oryza sativa L.)

Abstract

Starch, the major component of cereal grains including rice is composed of two types of α-polyglucan, amylose and amylopectin. Amylose forms a mainly linear structure, with glucose residues linked via α-1,4 bonds, whereas amylopectin has a highly ordered structure 1) with numerous branches linked to the middle of the linear structure by α-1,6 bonds. The ratio of amylose to amylopectin and the characteristics of the distribution of amylopectin chain-lengths affect the eating qualities and processing properties of cereal-based foods through changes in gelatinization and retrogradation of starch. Natural and induced mutants that have a defect in a gene encoding a starch-synthesizing enzyme and altered starch properties have been utilized in food production. For example, traditionally cultivated waxy rice, waxy maize, waxy barley, and the relatively recently bred waxy wheat 2) , which lack the granule-bound starch synthase I (GBSSI or Waxy) responsible for amylose synthesis have stickier or softer textures after cooking, and have been utilized for food products where such textures are desirable. In case of the rice mutants lacking starch branching enzyme IIb activity (amylose-extender or ae), the proportion of short-chains (degree of polymerisation (DP) 17 or less) of amylopectin is decreased and that of middle-length chains (DP 18 to 36) is increased, which results in higher gelatinization temperatures (GTs) and faster retrogradation of gelatinazed starch.3) This type of maize is known as amylomaize and is utilized for the production of resistant starch 4) : i.e., starch that cannot be digested by the human small intestine and therefore acts as a dietary fiber with many health benefits. Lack of starch synthase IIa (SSIIa) function causes changes in chain-length distribution: in rice, 5) barley, 6) wheat 7) and maize, 8) there is an

Mutants that have shorter amylopectin chains are promising materials for slow-hardening rice bread

“…3 and 4). In rice, single-locus recessive mutations of SbeI and the lack of starch phosphorylase activity result in shorter amylopectin chains (Okamoto et al, 2013a;Satoh et al, 2008). Unfortunately, mutants of wheat that lack SBEI activity have been produced but show no significant effects on the chain-length of amylopectin (Regina et al, 2004).…”

“…'Hiderishirazu D' and 'Kurnai' are natural loss-of-function mutants of SbeI. The mutations of 'Hiderishirazu D' and 'Kurnai' are considered to be of common origin, because no difference was detected between the DNA sequences of SbeI between 'Hiderishirazu D' and 'Kurnai' (Okamoto et al, 2013a). 'Akita Sake 44' is a gamma-ray-induced mutant with a low gelatinization temperature (Okamoto, unpublished result).…”

“…Nevertheless, there is room to improve these cultivars in order to introduce them to wider areas; 'Hiderishirazu D' and 'Kurnai' are upland cultivars and 'Akita Sake 44' is a cultivar for Japanese rice wine. A DNA marker that detects the mutant allele of SbeI is available (Okamoto et al, 2013a) and useful for selecting and breeding cultivars for slow-hardening rice bread. Okamoto et al (2013b) reported that 'Akita Sake 44' possesses SBEI activity.…”

“…Therefore, we hypothesized that softer bread (both gluten-containing and gluten-free) can be made by using cultivars that have shorter amylopectin chains than those in S-type amylopectin. Rice mutants of starch branching enzyme I (SbeI) have a high proportion of shorter amylopectin chains and a lower gelatinization temperature compared with cultivars that have regular Stype amylopectin (Okamoto et al, 2013a;Satoh et al, 2003). Here, we report that slow-hardening gluten-free and gluten-containing breads can be obtained by using mutants that have shorter amylopectin chains than those in S-type amylopectin.…”

Present status and future perspectives of breeding for buckwheat quality

“…Reserved starch of the mutant showed a low pasting temperature of rice flour and was rich in short chains of amylopectin. Rice cakes made from branching enzyme 1 (BEI)deficient lines with waxy starch can retain their softness for longer periods than rice cakes made from functional BEI lines (Okamoto et al 2013). Therefore, identification and development of BEI-deficient varieties in other cereal crops could extend the shelf life and improve the quality of waxy products made from cereal crops.…”