Cell wall lignification is a key step in forming functional endodermis and protoxylem (PX) in plant roots. Lignified casparian strips (CS) in endodermis and tracheary elements of PX are essential for selective absorption and transport of water and nutrients. Although multiple key regulators of CS and PX have been identified, the spatial information that drives the developmental shift to root lignification remains unknown. Here, we found that brassinosteroid (BR) signaling plays a key role in inhibiting root lignification in the root elongation zone. The inhibitory activity of BR signaling occurs partially through the direct binding of BRASSINAZOLE-RESISTANT 1 (BZR1) to SHORT-ROOT (SHR), repressing the SHR-mediated activation of downstream genes that are involved in root lignification. Upon entering the mature root zone, BR signaling declines rapidly, which releases SHR activity and initiates root lignification. Our results provide a mechanistic view of the developmental transition to cell wall lignification in Arabidopsis thaliana roots.

中文翻译：

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油菜素类固醇信号传导通过拮抗拟南芥中的短根功能来限制根木质化。

细胞壁木质化是植物根部形成功能性内皮层和原木质部（PX）的关键步骤。内皮层中的木质化凯氏带（CS）和 PX 的气管元件对于水和营养物质的选择性吸收和运输至关重要。尽管已经确定了 CS 和 PX 的多个关键调节因子，但驱动根木质化发育转变的空间信息仍然未知。在这里，我们发现油菜素类固醇（BR）信号在抑制根伸长区的根木质化中起着关键作用。BR 信号传导的抑制活性部分通过 BRASSINAZOLE-RESISTANT 1 (BZR1) 与 SHORT-ROOT (SHR) 的直接结合而发生，抑制 SHR 介导的参与根木质化的下游基因的激活。进入成熟根区后，BR 信号迅速减弱，从而释放 SHR 活性并启动根木质化。我们的结果提供了拟南芥根细胞壁木质化发育转变的机制观点。