Flag leaf angle impacts the photosynthetic capacity of densely grown plants and is thus an important agronomic breeding trait for crop architecture and yield. The hormone auxin plays a key role in regulating this trait, yet the underlying molecular and cellular mechanisms remain unclear. Here, we report that two rice (Oryza sativa) auxin response factors (ARFs), OsARF6 and OsARF17, which are highly expressed in lamina joint tissues, control flag leaf angle in response to auxin. Loss-of-function double osarf6 osarf17 mutants displayed reduced secondary cell wall levels of lamina joint sclerenchymatous cells (Scs), resulting in an exaggerated flag leaf angle and decreased grain yield under dense planting conditions. Mechanical measurements indicated that the mutant lamina joint tissues were too weak to support the weight of the flag leaf blade, resembling the phenotype of the rice increased leaf angle1 (ila1) mutant. We demonstrate that OsARF6 and OsARF17 directly bind to the ILA1 promoter independently and synergistically to activate its expression. In addition, auxin-induced ILA1 expression was dependent on OsARF6 and OsARF17. Collectively, our study reveals a mechanism that integrates auxin signaling with the secondary cell wall composition to determine flag leaf angle, providing breeding targets in rice, and potentially other cereals, for this key trait.

中文翻译：

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生长素响应因子 6 和 17 通过调节叶片接头的次生细胞壁生物合成来控制水稻的旗叶角

旗叶角度影响密集种植植物的光合能力，因此是作物结构和产量的重要农艺育种性状。激素生长素在调节这一性状中起关键作用，但其潜在的分子和细胞机制仍不清楚。在这里，我们报告了两种水稻 (Oryza sativa) 生长素响应因子 (ARF) OsARF6 和 OsARF17，它们在叶片关节组织中高表达，可控制旗叶角以响应生长素。功能丧失的双 osarf6 osarf17 突变体显示出叶片联合厚壁细胞 (Scs) 的次生细胞壁水平降低，导致在密集种植条件下的旗叶角过大和谷物产量下降。机械测量表明突变叶片关节组织太弱，无法支撑旗叶叶片的重量，类似于水稻表型增加的叶角1 (ila1) 突变体。我们证明 OsARF6 和 OsARF17 直接独立地和协同地与 ILA1 启动子结合以激活其表达。此外，生长素诱导的 ILA1 表达依赖于 OsARF6 和 OsARF17。总的来说，我们的研究揭示了一种将生长素信号传导与次生细胞壁组成相结合以确定旗叶角度的机制，为这一关键性状提供水稻和可能的其他谷物的育种目标。