Xian Fengjun, Liu Shuya, Huang Jishuai, Xie Bin, Zhu Lin, Zhang Qiannan, Lv Chen, Xu Yimeng, Zhang Xinrong, Hu Jun
State Key Laboratory of Hybrid Rice, Engineering Research Center for Plant Biotechnology and Germplasm Utilization of Ministry of Education, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China.
National Clinical Research Center of Kidney Diseases, Jinling Hospital, Medical School of Nanjing University, Nanjing, Jiangsu 210016, China.
Plant Physiol. 2025 Mar 28;197(4). doi: 10.1093/plphys/kiaf122.
Auxin plays an important role in various aspects of plant growth and development. However, the molecular mechanism underlying the control of grain size via auxin signaling pathways remains obscure. Here, we report that AUXIN/INDOLE-3-ACETIC ACID protein 3 (OsIAA3) positively regulates rice (Oryza sativa) grain size by promoting the cell expansion and proliferation of spikelet hulls. OsIAA3 interacted with 11 AUXIN RESPONSE FACTORS (ARFs), among which the interaction with OsARF16 was the strongest. The osarf16 knockout mutant showed smaller grains with decreased grain length, grain width, grain thickness, and 1,000-grain weight. Meanwhile, transgenic plants overexpressing OsARF16 produced noticeably larger grains with increased grain length and 1,000-grain weight. O. sativa BRASSINOSTEROID UPREGULATED 1-LIKE (OsBUL1), which encodes an atypical bHLH protein that positively regulates grain size by promoting cell expansion, is a direct target gene of OsARF16. The interaction between OsIAA3 and OsARF16 repressed the transcriptional activation of OsARF16 on OsBUL1. Our study reveals an OsIAA3-OsARF16-OsBUL1 module that regulates grain size, refining the molecular mechanism of the auxin signaling pathway involved in grain size control.
生长素在植物生长发育的各个方面都发挥着重要作用。然而，生长素信号通路调控籽粒大小的分子机制仍不清楚。在此，我们报道生长素/吲哚-3-乙酸蛋白3（OsIAA3）通过促进小穗颖壳细胞的扩张和增殖来正向调控水稻籽粒大小。OsIAA3与11个生长素响应因子（ARFs）相互作用，其中与OsARF16的相互作用最强。osarf16敲除突变体的籽粒变小，粒长、粒宽、粒厚和千粒重均降低。同时，过表达OsARF16的转基因植株产生明显更大的籽粒，粒长和千粒重增加。水稻油菜素类固醇上调1样蛋白（OsBUL1）是OsARF16的直接靶基因，它编码一种非典型bHLH蛋白，通过促进细胞扩张来正向调控籽粒大小。OsIAA3与OsARF16之间的相互作用抑制了OsARF16对OsBUL1的转录激活。我们的研究揭示了一个调控籽粒大小的OsIAA3-OsARF16-OsBUL1模块，完善了参与籽粒大小控制的生长素信号通路的分子机制。
