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Journal of Integrative Agriculture  2026, Vol. 25 Issue (7): 2688-2700    DOI: 10.1016/j.jia.2025.04.026
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SBEIIb is responsible for the chalk2 phenotype by regulating the formation of resistant starch in indica rice

Xinwei Li1*, Zihang Wang1*, Tianxiao Chen1, Shen Lin2, Guiai Jiao1, Shaoqing Tang1, Long Chen1, 3, Xiangjin Wei1#, Peisong Hu1#

1 State Key Laboratory of Rice Biology and Breeding/China National Center for Rice Improvement/China National Rice Research Institute, Hangzhou 311400, China

2 Huaiyin Institute of Agricultural Science in Xuhuai Region of Jiangsu, Huai’an 223001, China

3 Environment-friendly Crop Germplasm Innovation and Genetic Improvement Key Laboratory of Sichuan Province, Chengdu 610066, China

 Highlights 

A novel OsSBEIIb allele was identified in an indica rice mutant.
The OsSBEIIb mutation increases the resistant starch (RS) content in raw rice flour, as well as in retrograded and heated rice.
The chalk2 mutant serves as a valuable indica rice germplasm for breeding high-RS rice varieties.

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摘要  

高抗性淀粉稻米因其独特的健康功效而备受关注,其在改善2型糖尿病患者血糖控制、促进心血管健康及调节肠道菌群等方面具有重要应用前景。然而,高抗性淀粉水稻品种的选育仍存在诸多技术瓶颈。本研究从籼稻ZJ100的突变体库中鉴定出一个高垩白突变体chalk2,其直链淀粉与蛋白质含量显著升高,支链淀粉比例发生改变,同时总淀粉与脂质含量显著下降。抗性淀粉含量分析显示,chalk2中两类抗性淀粉(RS2RS3)含量较野生型大幅增加。chalk2突变体还表现出粒长、粒宽和粒厚减小,结实率下降,最终导致产量显著降低。通过连锁分析、Mut-Map分析和转基因互补实验,我们确定淀粉分支酶家族成员SBEIIb是导致chalk2表型的关键基因。SBEIIb是一个胚乳特异表达基因,编码蛋白定位于质体。进一步研究发现,chalk2突变体中SBEIIb的表达水平、酶活性和蛋白含量均显著降低,同时伴随多个淀粉合成代谢基因表达变化。这些结果表明,SBEIIb在调控籼稻淀粉组分及抗性淀粉形成过程中发挥核心作用。本研究揭示了SBEIIb调控籼稻中抗性淀粉形成的分子机制,为高抗性淀粉水稻的分子设计育种提供了重要理论依据和基因资源。



Abstract  

High-resistant starch rice is a valuable food for human health, especially for individuals with type 2 diabetes, as it supports effective blood sugar control and provides cardiovascular and intestinal benefits.  However, developing rice varieties with high resistant starch content remains a major challenge.  In this study, we identified a mutant, chalk2, with increased chalkiness from the mutant library of indica rice ZJ100.  The chalk2 mutants exhibited significantly higher amylose and protein contents, while total starch and lipid contents were reduced. Analysis of resistant starch in chalk2 revealed substantial increases in two resistant starch (RS) types RS2 and RS3.  Electron microscopy revealed abnormal starch granule development in the endosperm. The chalk2 mutant also showed reduced grain length, width, and thickness, as well as a decreased seed setting rate, which ultimately led to a significant reduction in grain yield.  Through physical localization, Mut-Map analysis, and transgene complementation, we found that SBEIIb was responsible for the chalk2 phynotypes, a member of the starch branching enzyme (SBE) family, specifically expressed in the endosperm.  Furthermore, the expression levels, enzyme activity, and protein abundance of SBEIIb were significantly reduced in chalk2 mutants.  These findings suggest that SBEIIb plays a crucial role in regulating the composition of starch and resistant starch formation in indica rice.

Keywords:  Oryza sativa       resistant starch        amylose        rice quality        rice yield  
Received: 13 February 2025   Accepted: 28 March 2025 Online: 18 April 2025  
Fund: 

This work was supported by grants from the National Natural Science Foundation of China (32372099 and 32188102), the Natural Science Foundation of Zhejiang Province, China (LQ24C130007), and the Innovation Program of Chinese Academy of Agricultural Sciences (CAAS-CSCB-202402).  

About author:  Xinwei Li, E-mail: lixinwei162013@163.com; #Correspondence Peisong Hu, Tel/Fax: +86-571-63370221, E-mail: peisonghu@126.com; Xiangjin Wei, Tel/Fax: +86-571-63370080, E-mail: weixiangjin@caas.cn * These authors contributed equally to this study.

Cite this article: 

Xinwei Li, Zihang Wang, Tianxiao Chen, Shen Lin, Guiai Jiao, Shaoqing Tang, Long Chen, Xiangjin Wei, Peisong Hu. 2026. SBEIIb is responsible for the chalk2 phenotype by regulating the formation of resistant starch in indica rice. Journal of Integrative Agriculture, 25(7): 2688-2700.

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