• Root hairs (RHs) develop from specialized epidermal trichoblast cells, whereas epidermal cells that lack RHs are known as atrichoblasts. The mechanism controlling RH cell fate is only partially understood.
• RH cell fate is regulated by a transcription factor complex that promotes the expression of the homeodomain protein GLABRA 2 (GL2), which blocks RH development by inhibiting ROOT HAIR DEFECTIVE 6 (RHD6). Suppression of GL2 expression activates RHD6, a series of downstream TFs including ROOT HAIR DEFECTIVE 6 LIKE‐4 (RSL4) and their target genes, and causes epidermal cells to develop into RHs. Brassinosteroids (BRs) influence RH cell fate. In the absence of BRs, phosphorylated BIN2 (a Type‐II GSK3‐like kinase) inhibits a protein complex that regulates GL2 expression.
• Perturbation of the arabinogalactan peptide (AGP21) in Arabidopsis thaliana triggers aberrant RH development, similar to that observed in plants with defective BR signaling. We reveal that an O ‐glycosylated AGP21 peptide, which is positively regulated by BZR1, a transcription factor activated by BR signaling, affects RH cell fate by altering GL2 expression in a BIN2‐dependent manner.
• Changes in cell surface AGP disrupts BR responses and inhibits the downstream effect of BIN2 on the RH repressor GL2 in root epidermis.

中文翻译：

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细胞表面阿拉伯半乳聚糖肽影响根毛细胞命运

• 根毛（RHs）由专门的表皮毛发成年细胞发育而成，而缺乏RHs的表皮细胞被称为成纤维细胞。控制RH细胞命运的机制只是部分了解。
• RH细胞的命运受到转录因子复合物的调控，该复合物可促进同源域蛋白GLABRA 2（GL2）的表达，该蛋白通过抑制根毛形成缺陷6（RHD6）阻止RH的发育。GL2表达的抑制会激活RHD6，RHD6是一系列下游TF，包括ROOT HAIR DEFECTIVE 6 LIKE-4（RSL4）及其靶基因，并导致表皮细胞发育为RH。油菜素类固醇（BRs）影响RH细胞的命运。在没有BR的情况下，磷酸化的BIN2（II型GSK3类激酶）可抑制调节GL2表达的蛋白质复合物。
• 拟南芥中阿拉伯半乳聚糖肽（AGP21）的扰动会触发RH异常发育，类似于在BR信号缺陷的植物中观察到的异常。我们发现，O-糖基化的AGP21肽受到BZR1（BR信号激活的转录因子）的正调控，通过改变BIN2依赖性的GL2表达来影响RH细胞的命运。
• 细胞表面AGP的变化会破坏BR反应，并抑制BIN2对根表皮中RH阻遏物GL2的下游作用。