In plants, the organ size is one of the most important features and regulated by an elaborate developmental program involving both internal and external signals. The steroidal hormone brassinosteroid (BR) plays an important role in regulating the organ size. BRASSINAZOLE RESISTANT 1 (BZR1) is one of important transcription factors that regulate organ size in BR signal pathway in Arabidopsis. The function of BZR1 on organ size is well characterized in Arabidopsis, but poorly understood in maize (Zea mays). To understand the mechanism of intrinsic organ size regulated by BZR1 during organogenesis, we identified the maize BZR1 and examined its function in Arabidopsis. Overexpression of ZmBZR1 displayed phenotypes of enlarged cotyledons, rosette leaves, floral organ and seed size in Arabidopsis. The cells in rosette leaves as well as other organs in transgenic ZmBZR1 lines were dramatically larger and longer than those in Col-0. ChIP and RNA-seq analysis showed ZmBZR1 can directly bind to the promoter region of organ size related genes, Germination Repression and Cell Expansion receptor-like kinase (GRACE) and KIP-RELATED PROTEIN6 (KRP6) to regulate their expression, suggesting ZmBZR1 is required for the progressive increase in cells during Arabidopsis development. Collectively, our findings provide significant insights into the mechanisms underlying regulation of organ size mediated by maize BZR1.

中文翻译：

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拟南芥中玉米 BR 转录因子 ZmBZR1 的过表达扩大了转基因植物的器官和种子大小

在植物中，器官大小是最重要的特征之一，并由涉及内部和外部信号的复杂发育程序调节。甾体激素油菜素类固醇 (BR) 在调节器官大小方面起着重要作用。BRASSINAZOLE RESISTANT 1 (BZR1)是拟南芥BR信号通路中调节器官大小的重要转录因子之一。BZR1 对器官大小的功能在拟南芥中得到了很好的表征，但在玉米（Zea mays）中却知之甚少。为了了解器官发生过程中 BZR1 调节内在器官大小的机制，我们鉴定了玉米 BZR1 并检查了其在拟南芥中的功能。ZmBZR1 的过表达在拟南芥中表现出增大的子叶、莲座叶、花器官和种子大小的表型。转基因 ZmBZR1 系中莲座叶和其他器官中的细胞比 Col-0 中的细胞大得多且长得多。ChIP 和 RNA-seq 分析显示 ZmBZR1 可以直接结合器官大小相关基因、萌发抑制和细胞扩张受体样激酶 (GRACE) 和 KIP-RELATED PROTEIN6 (KRP6) 的启动子区域来调节它们的表达，表明需要 ZmBZR1用于拟南芥发育过程中细胞的逐渐增加。总的来说，我们的研究结果为玉米 BZR1 介导的器官大小调节机制提供了重要的见解。萌发抑制和细胞扩张受体样激酶 (GRACE) 和 KIP 相关蛋白 6 (KRP6) 来调节它们的表达，表明在拟南芥发育过程中细胞的逐渐增加需要 ZmBZR1。总的来说，我们的研究结果为玉米 BZR1 介导的器官大小调节机制提供了重要的见解。萌发抑制和细胞扩张受体样激酶 (GRACE) 和 KIP 相关蛋白 6 (KRP6) 来调节它们的表达，表明在拟南芥发育过程中细胞的逐渐增加需要 ZmBZR1。总的来说，我们的研究结果为玉米 BZR1 介导的器官大小调节机制提供了重要的见解。