Distinct RopGEFs Successively Drive Polarization and Outgrowth of Root Hairs
Distinct RopGEFs Successively Drive Polarization and Outgrowth of Root Hairs
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DOI：
10.1016/j.cub.2019.04.059
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发表时间：
2019-06-03
期刊：
影响因子：
9.2
通讯作者：
Grossmann, Guido
中科院分区：
文献类型：
--
作者：
Denninger, Philipp;Reichelt, Anna;Grossmann, Guido
根毛是根表皮的管状突起，显著扩大了根际可利用的土壤体积。成毛细胞是负责根毛形成的细胞类型，通过生长机制极化至质膜上预定义的根毛起始域（RHID），从细胞伸长切换至尖端生长。这种极性结构域的出现类似于其他真核系统中细胞极性的建立[1-3]。植物Rho型GTP酶（ROP）是RHID的第一个分子决定因子[4，5]，后来在极性生长中发挥核心作用[6]。许多研究已经阐明了在细胞中定位RHID [7-9]或调节ROP活性[10-18]的机制。然而，将ROP靶向至RHID并启动产物生长的分子参与者尚未被鉴定。我们解剖了极化毛细胞中生长机制组装的时间，发现分子参与者和产物的定位是时间上独立的过程，每个过程都由特定的ROP鸟嘌呤核苷酸交换因子（GEF）控制。对毛胚细胞特异性GEF的功能分析显示，GEF 3是正常ROP极化所需的，因此是有效的根毛出现，而GEF 4主要调节随后的尖端生长。GEF 3的异位表达诱导在其他细胞类型中形成空间受限的ROP募集结构域，表明GEF 3在细胞极化期间充当膜地标的作用。
Root hairs are tubular protrusions of the root epidermis that significantly enlarge the exploitable soil volume in the rhizosphere. Trichoblasts, the cell type responsible for root hair formation, switch from cell elongation to tip growth through polarization of the growth machinery to a predefined root hair initiation domain (RHID) at the plasma membrane. The emergence of this polar domain resembles the establishment of cell polarity in other eukaryotic systems [1-3]. Rho-type GTPases of plants (ROPs) are among the first molecular determinants of the RHID [4, 5], and later play a central role in polar growth [6]. Numerous studies have elucidated mechanisms that position the RHID in the cell [7-9] or regulate ROP activity [10-18]. The molecular players that target ROPs to the RHID and initiate outgrowth, however, have not been identified. We dissected the timing of the growth machinery assembly in polarizing hair cells and found that positioning of molecular players and outgrowth are temporally separate processes that are each controlled by specific ROP guanine nucleotide exchange factors (GEFs). A functional analysis of trichoblast-specific GEFs revealed GEF3 to be required for normal ROP polarization and thus efficient root hair emergence, whereas GEF4 predominantly regulates subsequent tip growth. Ectopic expression of GEF3 induced the formation of spatially confined, ROP-recruiting domains in other cell types, demonstrating the role of GEF3 to serve as a membrane landmark during cell polarization.