J Integr Plant Biol. ›› 2022, Vol. 64 ›› Issue (10): 1883-1900.DOI: 10.1111/jipb.13333

• Cell and Developmental Biology • Previous Articles     Next Articles

Ribonuclease H-like gene SMALL GRAIN2 regulates grain size in rice through brassinosteroid signaling pathway

Yunshuai Huang1†, Hui Dong1†, Changling Mou1†, Ping Wang1, Qixian Hao1, Min Zhang1, Hongmin Wu1, Fulin Zhang1, Tengfei Ma1, Rong Miao1, Kai Fu1, Yaping Chen1, Ziyan Zhu1, Cheng Chen1, Qikai Tong1, Zhuoran Wang1, Shirong Zhou1, Xi Liu1, Shijia Liu1, Yunlu Tian1, Ling Jiang1* and Jianmin Wan1,2*   

  1. 1 State Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Nanjing National Field Scientific Observation and Research Station for Rice Germplasm, Nanjing Agricultural University, Nanjing 210095, China
    2 National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China

    These authors contributed equally to this work.
    * Correspondences: Ling Jiang (jiangling@njau.edu.cn); Jianmin Wan (wanjm@njau.edu.cn). Drs. Wan and Jiang are fully responsible for the distribution of the materials associated with this article.
  • Received:2022-06-09 Accepted:2022-07-28 Online:2022-07-29 Published:2022-10-01

Abstract: Grain size is a key agronomic trait that determines the yield in plants. Regulation of grain size by brassinosteroids (BRs) in rice has been widely reported. However, the relationship between the BR signaling pathway and grain size still requires further study. Here, we isolated a rice mutant, named small grain2 (sg2), which displayed smaller grain and a semi-dwarf phenotype. The decreased grain size was caused by repressed cell expansion in spikelet hulls of the sg2 mutant. Using map-based cloning combined with a MutMap approach, we cloned SG2, which encodes a plant-specific protein with a ribonuclease H-like domain. SG2 is a positive regulator downstream of GLYCOGEN SYNTHASE KINASE2 (GSK2) in response to BR signaling, and its mutation causes insensitivity to exogenous BR treatment. Genetical and biochemical analysis showed that GSK2 interacts with and phosphorylates SG2. We further found that BRs enhance the accumulation of SG2 in the nucleus, and subcellular distribution of SG2 is regulated by GSK2 kinase activity. In addition, Oryza sativa OVATE family protein 19 (OsOFP19), a negative regulator of grain shape, interacts with SG2 and plays an antagonistic role with SG2 in controlling gene expression and grain size. Our results indicated that SG2 is a new component of GSK2-related BR signaling response and regulates grain size by interacting with OsOFP19.

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