背景回顾：Arabidopsis (Arabidopsis thaliana) root hairs develop as long tubular extensions from the rootward pole of trichoblasts and exert polarized tip growth. 

研究基础：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). Loss-of-functionrhd2 mutants have short root hairs that are unable to elongate by tip growth, and this phenotype is fully complemented by GFP-RHD2 expressed under the RHD2 promoter. 

提出问题：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.

主要研究：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. 

结果1-TGN隔室：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 corresponds with the stage of root hair formation. 

结果2-TGN和早期核内体：Movements of TGN/early endosomes, but not late endosomes, were affected in the bulging domains of the rhd2-1 mutant. 

结果3-甾醇：Finally, we revealed that structural sterols might be involved in the accumulation, docking, and incorporation of TGN compartments containing GFP-RHD2 to the apical PM of root hairs.

结论：These results help clarifying 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.

 摘 要 

拟南芥的根毛是从朝向根侧的毛体细胞极长出的长条管状延伸，存在极性顶端生长。根毛极性的建立和维持是一个复杂的过程，其中涉及到了由NADPH氧化酶AtRBOHC/RHD2介导的局部活性氧物质（ROS）产生。rhd2突变会导致根毛变短，顶端生长不能伸长，并且该表型缺陷能够通过RHD2启动子驱动的GFP-RHD2表达互补。但是，根毛起始和顶端生长时，AtRBOHC/RHD2亚细胞再分布以及转运到质膜的时空机制还不清楚。本文中，作者利用显微观察对含有GFP-RHD2的囊泡隔室进行了定性和定量分析，并且解析了其在正在发育的凸起及正在生长的根毛中的作用。通过独立的标记所鉴定的反面高尔基网络（TGN）等隔室会将GFP-RHD2转运至顶端质膜域，其程度与根毛形成的阶段相对应。在rhd2-1突变体中，TGN和早期核内体，而非晚期核内体的移动在凸起结构域中受到影响。最后，作者发现结构甾醇可能参与了含有GFP-RHD2的TGN隔室在根毛顶端质膜的积累、对接和结合。本文的研究结果有助于阐明顶端质膜结构域中极性的AtRBOHC/RHD2蛋白靶向、维持和再循环机制，使其与根毛起始和生长的不同发育阶段相协调。