The presence of small tooth-like indentations, or serrations, characterizes leaf margins of Arabidopsis thaliana plants. The NAC family member CUC2, which undergoes post-transcriptional gene silencing by three micro RNA genes (MIR164A, B, and C), controls the extension of leaf serration. Here we analyzed the role of AtHB1, a transcription factor (TF) belonging to the homeodomain-leucine zipper subfamily I, in shaping leaf margins. Using mutants with an impaired silencing pathway as background, we obtained transgenic plants expressing AtHB1 over 100 times compared to controls. These plants presented an atypical developmental phenotype characterized by leaves with deep serration. Transcript measurements revealed that CUC2 expression was induced in plants overexpressing AtHB1 and repressed in athb1 mutants, indicating a positive regulation exerted by this TF. Moreover, molecular analyses of AtHB1 overexpressing and mutant plants revealed that AtHB1 represses MIR164 transcription. We found that overexpression of MIR164B was able to reverse the serration phenotype of plants overexpressing AtHB1. Finally, chromatin immunoprecipitation assays revealed that AtHB1 was able to bind in vivo the promoter regions of all three MIR164 encoding loci. Altogether, our results indicate that AtHB1 directly represses MIR164 expression to enhance leaf serration by increasing CUC2 levels.

中文翻译：

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AtHB1转录因子控制miR164-CUC2调节节点以调节叶片发育。

拟南芥植物叶片边缘的小齿状锯齿或锯齿的存在。NAC家族成员CUC2（通过三个微RNA基因（MIR164A，B和C）经历转录后基因沉默）控制着叶片锯齿的延伸。在这里，我们分析了AtHB1（一种转录因子，属于同源域-亮氨酸拉链亚家族I）在塑造叶缘中的作用。使用沉默途径受损的突变体作为背景，与对照相比，我们获得了表达AtHB1的转基因植物超过100倍。这些植物表现出非典型的发育表型，其特征是具有深锯齿的叶片。转录本测量结果表明，在过量表达AtHB1的植物中诱导了CUC2表达，而在athb1突变体中却抑制了CUC2的表达，表示此TF施加了积极的调节作用。此外，对AtHB1过表达和突变植物的分子分析表明，AtHB1抑制MIR164转录。我们发现，MIR164B的过表达能够逆转过表达AtHB1的植物的锯齿状表型。最后，染色质免疫沉淀试验表明AtHB1能够在体内结合所有三个MIR164编码基因座的启动子区域。总之，我们的结果表明AtHB1直接抑制MIR164表达，通过增加CUC2水平来增强叶片的锯齿。染色质免疫沉淀试验表明，AtHB1能够在体内结合所有三个MIR164编码基因座的启动子区域。总之，我们的结果表明AtHB1直接抑制MIR164表达，通过增加CUC2水平来增强叶片的锯齿。染色质免疫沉淀试验表明，AtHB1能够在体内结合所有三个MIR164编码基因座的启动子区域。总之，我们的结果表明AtHB1直接抑制MIR164表达，通过增加CUC2水平来增强叶片的锯齿。