Grain size and weight are crucial yield-related traits in rice (Oryza sativa). Although certain key genes associated with rice grain size and weight have been successfully cloned, the molecular mechanisms underlying grain size and weight regulation remain elusive. Here, we identified a molecular pathway regulating grain size and weight in rice involving the MPS ONE BINDER KINASE ACTIVATOR-LIKE 1A–SERINE/THREONINE-PROTEIN KINASE 38–CYCLIN C (OsMOB1A–OsSTK38–OsCycC) module. OsSTK38 is a nuclear Dbf2-related kinase that positively regulates grain size and weight by coordinating cell proliferation and expansion in the spikelet hull. OsMOB1A interacts with and enhances the autophosphorylation of OsSTK38. Specifically, the critical role of the OsSTK38 S322 site in its kinase activity is highlighted. Furthermore, OsCycC, a component of the Mediator complex, was identified as a substrate of OsSTK38, with enhancement by OsMOB1A. Notably, OsSTK38 phosphorylates the T33 site of OsCycC. The phosphorylation of OsCycC by OsSTK38 influenced its interaction with the transcription factor KNOTTED-LIKE HOMEOBOX OF ARABIDOPSIS THALIANA 7 (OsKNAT7). Genetic analysis confirmed that OsMOB1A, OsSTK38 and OsCycC function in a common pathway to regulate grain size and weight. Taken together, our findings revealed a connection between the Hippo signalling pathway and the Cyclin-Dependent Kinase (CDK) module in eukaryotes. Moreover, they provide insights into the molecular mechanisms linked to yield-related traits and propose innovative breeding strategies for high-yielding varieties.

中文翻译：

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OsMOB1A–OsSTK38 激酶复合体磷酸化 CYCLIN C，控制水稻的颗粒大小和重量

籽粒大小和重量是水稻 (Oryza sativa) 中与产量相关的重要性状。尽管与水稻籽粒大小和重量相关的某些关键基因已被成功克隆，但籽粒大小和重量调节的分子机制仍然难以捉摸。在这里，我们确定了调节水稻籽粒大小和重量的分子途径，涉及 MPS ONE BINDER KINASE ACTIVATOR-LIKE 1A–丝氨酸/苏氨酸蛋白激酶 38–CYCLIN C (OsMOB1A–OsSTK38–OsCycC) 模块。 OsSTK38 是一种核 Dbf2 相关激酶，通过协调小穗壳中的细胞增殖和扩张来正向调节颗粒大小和重量。 OsMOB1A 与 OsSTK38 相互作用并增强其自身磷酸化。具体来说，OsSTK38 S322 位点在其激酶活性中的关键作用得到了强调。此外，介体复合物的一个组成部分 OsCycC 被确定为 OsSTK38 的底物，并受到 OsMOB1A 的增强。值得注意的是，OsSTK38 磷酸化 OsCycC 的 T33 位点。 OsSTK38 对 OsCycC 的磷酸化影响了其与转录因子拟南芥 KNOTTED-LIKE HOMEOBOX 7 (OsKNAT7) 的相互作用。遗传分析证实 OsMOB1A、OsSTK38 和 OsCycC 在调节籽粒大小和重量的共同途径中发挥作用。总而言之，我们的研究结果揭示了真核生物中 Hippo 信号通路与细胞周期蛋白依赖性激酶 (CDK) 模块之间的联系。此外，他们还提供了对与产量相关性状相关的分子机制的见解，并提出了高产品种的创新育种策略。