Arabidopsis root hairs develop as long tubular extensions from the rootward pole of trichoblasts and exert polarized tip growth. The establishment and maintenance of root hair polarity is a complex process involving the local apical production of reactive oxygen species (ROS) generated by NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG PROTEIN C/ROOT HAIR DEFECTIVE 2 (AtRBOHC/RHD2). It has been shown that loss-of-function rhd2 mutants have short root hairs that are unable to elongate by tip growth, and this phenotype was fully complemented by GFP-RHD2 expressed under the RHD2 promoter. However, the spatiotemporal mechanism of AtRBOHC/RHD2 subcellular redistribution and delivery to the plasma membrane (PM) during root hair initiation and tip growth are still unclear. Here, we used advanced microscopy for detailed qualitative and quantitative analysis of vesicular compartments containing GFP-RHD2 and characterization of their movements in developing bulges and growing root hairs. These compartments, identified by an independent marker such as the trans-Golgi network (TGN), deliver GFP-RHD2 to the apical PM domain, the extent of which correlates with the stage of root hair formation. Movements of TGN/early endosomes, but not late endosomes, were affected in the bulging domains of the rhd2-1 mutant. Finally, we reveal that accumulation in the growing tip, docking, and incorporation of TGN compartments containing GFP-RHD2 to the apical PM of root hairs requires structural sterols. These results help clarify the mechanism of polarized AtRBOHC/RHD2 targeting, maintenance, and recycling at the apical PM domain, coordinated with different developmental stages of root hair initiation and growth.

中文翻译：

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AtRBOHC/RHD2 在根毛发育过程中向顶端质膜结构域的囊泡递送

拟南芥根毛从毛胚细胞的根部向长管状延伸，并产生极化的尖端生长。根毛极性的建立和维持是一个复杂的过程，涉及由 NADPH 氧化酶呼吸爆发氧化酶同源蛋白 C/ROOT HAIR DEFECTIVE 2 (AtRBOHC/RHD2) 产生的活性氧 (ROS) 的局部顶端产生。它已经显示出失功能RHD2突变体具有短的根毛那些无法通过顶端生长伸长，并且该表型是由GFP-RHD2充分补充了下表达RHD2发起人。然而，AtRBOHC/RHD2 亚细胞在根毛起始和尖端生长过程中重新分布和传递到质膜 (PM) 的时空机制仍不清楚。在这里，我们使用先进的显微镜对含有 GFP-RHD2 的囊泡隔室进行详细的定性和定量分析，并表征它们在发育中的凸起和生长的根毛中的运动。这些由独立标记物（如跨高尔基网络 (TGN)）识别的隔室将 GFP-RHD2 传递到根尖 PM 域，其程度与根毛形成阶段相关。TGN/早期内体的运动，但不是晚期内体，在rhd2-1的膨胀区域受到影响突变体。最后，我们揭示了含有 GFP-RHD2 的 TGN 区室在生长尖端、对接和合并到根毛顶端 PM 的积累需要结构甾醇。这些结果有助于阐明根尖 PM 域极化 AtRBOHC/RHD2 靶向、维持和回收的机制，与根毛起始和生长的不同发育阶段相协调。