Leaf angle (LA) is a crucial factor that affects planting density and yield in maize. However, the regulatory mechanisms underlying LA formation remain largely unknown. In this study, we performed a comparative histological analysis of the ligular region across various maize inbred lines and revealed that LA is significantly influenced by a two-step regulatory process involving initial cell elongation followed by subsequent lignification in the ligular adaxial sclerenchyma cells (SCs). Subsequently, we performed both bulk and single-nucleus RNA sequencing, generated a comprehensive transcriptomic atlas of the ligular region, and identified numerous genes enriched in the hypodermal cells that may influence their specialization into SCs. Furthermore, we functionally characterized two genes encoding atypical basic-helix–loop–helix (bHLH) transcription factors, bHLH30 and its homolog bHLH155, which are highly expressed in the elongated adaxial cells. Genetic analyses revealed that bHLH30 and bHLH155 positively regulate LA expansion, and molecular experiments demonstrated their ability to activate the transcription of genes involved in cell elongation and lignification of SCs. These findings highlight the specialized functions of ligular adaxial SCs in LA regulation by restricting further extension of ligular cells and enhancing mechanical strength. The transcriptomic atlas of the ligular region at single-nucleus resolution not only deepens our understanding of LA regulation but also enables identification of numerous potential targets for optimizing plant architecture in modern maize breeding.

中文翻译：

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组织学和单核转录组分析揭示了玉米叶角厚壁细胞的特殊功能和叶角的关键调节因子


叶角（LA）是影响玉米种植密度和产量的关键因素。然而，LA 形成的调控机制仍然很大程度上未知。在这项研究中，我们对不同玉米自交系的叶状区域进行了比较组织学分析，结果表明，LA 受到两步调控过程的显着影响，该过程涉及初始细胞伸长，随后是叶状近轴巩膜细胞 (SC) 的木质化。随后，我们进行了批量和单核 RNA 测序，生成了舌状区的全面转录组图谱，并鉴定了皮下细胞中富集的许多基因，这些基因可能会影响它们专门化为 SC。此外，我们对编码非典型碱性螺旋-环-螺旋（bHLH）转录因子的两个基因（bHLH30 及其同源物 bHLH155）进行了功能表征，它们在细长的近轴细胞中高度表达。遗传分析表明，bHLH30 和 bHLH155 正向调节 LA 扩张，分子实验证明它们能够激活参与 SC 细胞伸长和木质化的基因转录。这些发现强调了叶状近轴 SC 通过限制叶状细胞的进一步延伸和增强机械强度在 LA 调节中的特殊功能。单核分辨率的叶区转录组图谱不仅加深了我们对 LA 调控的理解，而且还能够识别现代玉米育种中优化植物结构的许多潜在目标。