SummaryResistant starch (RS) is a special kind of starch with beneficial effects on obesity, type 2 diabetes and other chronic complications. Breeding high‐RS rice varieties is considered a valuable way to improve public health. However, most rice cultivars only contain an RS level lower than 2% in cooked rice, and cloning of RS genes is critical to improve RS levels in rice. The loss of function of Starch Synthases IIIa (SSIIIa) and SSIIIb, two amylopectin biosynthetic genes, could elevate RS levels up to 10%. Here, we performed a systematic genetic study of 14 amylopectin biosynthetic genes in the ssIIIa ssIIIb double mutant via genome editing, and investigated their effects on RS formation, the eating quality and grain yield. The results showed that deficiency in SSIIa, SSIVb or ISA2 under the ssIIIa ssIIIb background could each elevate RS content to above 14%, and the quadruple mutants of sbeI sbeIIb ssIIIa ssIIIb and sbeI ssIVb ssIIIa ssIIIb could further increase RS levels to over 18%. Furthermore, the eating quality of cooked rice and grain yield decreased along with the elevated RS contents, showing a trade‐off among these traits. In these mutants, ssIIIa ssIIIb showed the balanced performance of RS and grain yield. This study provides insights into RS biosynthesis with a series of RS genes in the amylopectin biosynthesis pathway and practical strategy to breed high‐RS rice varieties with balanced performance.

中文翻译：

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通过在 rs4 中系统编辑支链淀粉素生物合成基因来创造高抗性淀粉稻


摘要抗性淀粉 （RS） 是一种特殊的淀粉，对肥胖、2 型糖尿病和其他慢性并发症有有益作用。培育高 RS 水稻品种被认为是改善公共卫生的宝贵方法。然而，大多数水稻品种在米饭中的 RS 水平仅低于 2%，克隆 RS 基因对于提高水稻中的 RS 水平至关重要。淀粉合酶 IIIa （SSIIIa） 和 SSIIIb 这两个支链淀粉生物合成基因的功能丧失可能会使 RS 水平升高高达 10%。本研究通过基因组编辑对 ssIIIa ssIIIb 双突变体中的 14 个支链淀粉生物合成基因进行了系统遗传研究，研究了它们对 RS 形成、食用品质和谷物产量的影响。结果表明，在 ssIIIa ssIIIb 背景下，SSIIa 、 SSIVb 或 ISA2 的缺陷均可使 RS 含量升高到 14% 以上，而 sbeI sbeIIb ssIIIa ssIIIb 和 sbeI ssIVb ssIIIa ssIIIb 的四重突变体可进一步使 RS 水平升高至 18% 以上。此外，随着 RS 含量的升高，熟米的食用品质和谷物产量下降，表明这些性状之间存在权衡。在这些突变体中，ssIIIa ssIIIb 表现出 RS 和籽粒产量的平衡表现。本研究利用支链淀粉生物合成途径中的一系列 RS 基因为 RS 生物合成提供了见解，并提供了培育性能均衡的高 RS 水稻品种的实用策略。