Background

Cereals high in resistant starch (RS) are gaining popularity, as their intake is thought to help manage diabetes and prediabetes. Number of patients suffering from diabetes is also increasing in Asian countries where people consume rice as a staple food, hence generation of practically growable high RS rice line has been anticipated. It is known that suppression of starch branching enzyme (BE) IIb increases RS content in cereals. To further increase RS content and for more practical use, we generated a non-transgenic be1 be2b double mutant rice (Oryza sativa) line, which completely lacked both proteins, by crossing a be1 mutant with a be2b mutant.

Results

The be1 be2b mutant showed a decrease in intermediate amylopectin chains and an increase in long amylopectin chains compared with be2b. The amylose content of be1 be2b mutant (51.7%) was the highest among all pre-existing non-transgenic rice lines. To understand the effects of chewing cooked rice and cooking rice flour on RS content, RS content of mashed and un-mashed cooked rice as well as raw and gelatinized rice flour were measured using be1 be2b and its parent mutant lines. The RS contents of mashed cooked rice and raw rice flour of be1 be2b mutant (28.4% and 35.1%, respectively) were 3-fold higher than those of be2b mutant. Gel-filtration analyses of starch treated with digestive enzymes showed that the RS in be1 be2b mutant was composed of the degradation products of amylose and long amylopectin chains. Seed weight of be1 be2b mutant was approximately 60% of the wild type and rather heavier than that of be2b mutant.

Conclusions

The endosperm starch in be1 be2b double mutant rice were enriched with long amylopectin chains. This led to a great increase in RS content in cooked rice grains and rice flour in be1 be2b compared with be2b single mutant. be1 be2b generated in this study must serve as a good material for an ultra-high RS rice cultivar.

中文翻译：

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超高水平抗性淀粉非转基因 BEI 和 BEIIb 双突变水稻 ( Oryza sativa ) 的产生和淀粉特性

 背景

富含抗性淀粉 (RS) 的谷物越来越受欢迎，因为人们认为摄入它们有助于控制糖尿病和糖尿病前期。在人们以大米为主食的亚洲国家中，患有糖尿病的患者数量也在增加，因此预计将产生可实际种植的高RS水稻品系。众所周知，抑制淀粉分支酶 (BE) IIb 会增加谷物中的 RS 含量。为了进一步增加RS含量并实现更实际的用途，我们通过将be1突变体与be2b突变体杂交，产生了完全缺乏这两种蛋白质的非转基因be1 be2b双突变体水稻（ Oryza sativa ）品系。

 结果

与be2b相比， be1 be2b突变体表现出中间支链淀粉链的减少和长支链淀粉链的增加。 be1 be2b突变体的直链淀粉含量(51.7%)是所有现有非转基因水稻品系中最高的。为了了解咀嚼熟米和煮米粉对 RS 含量的影响，使用be1 be2b及其亲本突变体系测量了捣碎和未捣碎的熟米以及生米和糊化米粉的 RS 含量。 be1 be2b突变体的熟米泥和生米粉的RS含量（分别为28.4%和35.1%）是be2b突变体的3倍。对消化酶处理淀粉的凝胶过滤分析表明， be1 be2b突变体中的 RS 由直链淀粉和长支链淀粉链的降解产物组成。 be1 be2b突变体的种子重量约为野生型的 60%，并且比be2b突变体重得多。

 结论

be1 be2b双突变体水稻的胚乳淀粉富含长支链淀粉。这导致be1 be2b中熟米粒和米粉中RS含量较be2b单突变体大幅增加。本研究中产生的be1 be2b必定是培育超高 RS 水稻品种的良好材料。