J Integr Plant Biol ›› 2025, Vol. 67 ›› Issue (5): 1290-1306.DOI: 10.1111/jipb.13861

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  • 收稿日期:2024-11-25 接受日期:2025-01-15 出版日期:2025-05-01 发布日期:2025-05-12

SMALL AND ROUND GRAIN is involved in the brassinosteroid signaling pathway which regulates grain size in rice

Rong Miao1†, Qibing Lin2†, Penghui Cao1,3†, Chunlei Zhou2, Miao Feng2, Jie Lan1, Sheng Luo2, Fulin Zhang1, Hongmin Wu1, Qixian Hao1, Hai Zheng1, Tengfei Ma1, Yunshuai Huang1, Changling Mou1, Thanhliem Nguyen1,4, Zhijun Cheng2, Xiuping Guo2, Shijia Liu1, Ling Jiang1,5* and Jianmin Wan1,2,5*   

  1. 1. National Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, Jiangsu Nanjing National Field Scientific Observation and Research Station for Rice Germplasm, Nanjing Agricultural University, Nanjing 210095, China
    2. State Key Laboratory of Crop Gene Resource and Breeding, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China
    3. Suzhou Academy of Agricultural Sciences, Suzhou 215105, China
    4. Faculty of Natural Sciences, Quynhon University, Quynhon, Binhdinh 590000, Vietnam
    5. Zhongshan Biological Breeding Laboratory, Nanjing 210095, China

    †These authors contributed equally to this work.
    *Correspondences: Ling Jiang (jiangling@njau.edu.cn); Jianmin Wan (wanjm@njau.edu.cn, Dr. Wan is fully responsible for the distribution of all materials associated with this article)
  • Received:2024-11-25 Accepted:2025-01-15 Online:2025-05-01 Published:2025-05-12
  • Supported by:
    This research was supported by grants from STI 2030－Major Projects (2023ZD0406802), the National Key Research and Development Program of China (2022YFD1200104), the National Natural Science Foundation of China (32172024), Natural Science Foundation of Jiangsu Province, Major Project (BE2023362), and Program of Zhongshan Biological Breeding Laboratory (BM2022008‐03).

Abstract: Grain size is a key determinant of 1,000-grain weight, one of three factors determining grain yield. However, the complete regulatory network controlling grain size has not been fully clarified. Here, we identified a rice mutant, named small and round grain (srg) that exhibits semi-dwarf stature and small grain size. Cytological analysis showed that cell length and number of spikelet epidermal cells of the srg mutant are reduced, indicating that SRG controls grain size by promoting cell elongation and increasing cell number. SRG encodes a kinesin belonging to the kinesin-1 subfamily and is extensively expressed in different plant tissues with relatively high expression in young panicles. SRG protein is mainly located in the nucleus and cell membrane. Expression of the SRG gene was induced by brassinolide through the brassinosteroid (BR) responsive factor OsWRKY53 and SRG protein was phosphorylated by BR-activated kinase OsBSK3 to prevent its degradation. In addition, microtubule (MT) morphology was abnormal and disordered in the srg and cr-1 mutants. These findings suggest that BR likely stabilizes orderly assembly and arrangement of MTs by stabilizing SRG proteins, thus promoting grain size. SRG overexpression lines produced more tillers and significantly larger and heavier grains to increase 1,000-grain weight, suggesting that SRG has potential to increase grain yield. Our study indicated that SRG is a new BR responsive factor and BR might regulate grain size by influencing the expression of SRG.

Key words: BR signaling, grain size, OsBSK3, OsWRKY53, rice, Small and Round Grain (SRG)

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