The leaf margin is a fascinating feature of leaf morphology, contributing to the incredible diversity of leaf shapes and forms. As a central regulator of plant organ separation and margin development, CUP-SHAPED COTYLEDON2 (CUC2), a NAM, ATAF1, 2, CUC2 (NAC)-family transcription factor, governs the extent of serrations along the leaf margin. CUC2 activity is tightly regulated at transcriptional and posttranscriptional levels. However, the molecular mechanism that controls CUC2 transcription during leaf development has not been fully elucidated. Here we report that Arabidopsis (Arabidopsis thaliana) NGATHA-LIKE1 (NGAL1) to NGAL3, which are three related B3 family transcription factors, act as negative regulators of leaf margin serration formation. Over-expression of NGALs led to "cup-shaped" cotyledons and smooth leaf margins, whereas the triple loss-of-function mutant ngaltri exhibited more serrated leaves than the wild type. RNA-sequencing analyses revealed that the expression levels of a number of transcription factor genes involved in leaf development are regulated by NGALs, including CUC2. Comparative transcriptome analyses further uncovered a significant overlap between NGAL- and CUC2-regulated genes. Moreover, genetic analyses using various combinations of gain- and loss-of-function mutants of NGALs and CUC2 confirmed that CUC2 acts downstream of NGALs in promoting the formation of leaf-margin serrations. Finally, we demonstrate that NGAL1 directly binds to the CUC2 promoter causing repressed CUC2 expression. In summary, direct CUC2 transcriptional repression by NGAL1 characterizes a further regulatory module controlling leaf margin development.

叶缘是叶子形态的一个令人着迷的特征，有助于叶子形状和形式的令人难以置信的多样性。CUP-SHAPED COTYLEDON2 (CUC2) 是一种 NAM、ATAF1、2、CUC2 (NAC) 家族转录因子，作为植物器官分离和边缘发育的中央调节因子，控制沿叶缘锯齿的范围。CUC2 活性在转录和转录后水平受到严格调控。然而，叶片发育过程中控制CUC2转录的分子机制尚未完全阐明。在这里，我们报道拟南芥（Arabidopsis thaliana）NGATHA-LIKE1（NGAL1）至NGAL3，这三个相关的B3家族转录因子，充当叶缘锯齿形成的负调节因子。NGAL的过度表达导致“杯形”子叶和光滑的叶缘，而三重功能丧失突变体ngaltri表现出比野生型更多的锯齿状叶子。RNA测序分析表明，许多参与叶片发育的转录因子基因的表达水平受到NGAL的调节，包括CUC2。比较转录组分析进一步揭示了 NGAL 和 CUC2 调节基因之间的显着重叠。此外，使用NGAL和CUC2的功能获得和丧失功能突变体的各种组合进行的遗传分析证实，CUC2 在 NGAL 下游发挥作用，促进叶缘锯齿的形成。最后，我们证明 NGAL1 直接与CUC2启动子结合，导致CUC2表达受到抑制。总之，NGAL1 直接抑制CUC2转录是控制叶缘发育的进一步调控模块的特征。