Mapping the site of action of the Green Revolution hormone gibberellin.
Mapping the site of action of the Green Revolution hormone gibberellin.
复制标题
绘制绿色革命激素赤霉素的作用位点。
DOI：
10.1073/pnas.1301609110
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发表时间：
2013
影响因子：
11.1
通讯作者：
Band LR
中科院分区：
文献类型：
--
作者：
Band LR
赤霉素（GA）是一类促进植物生长和发育的关键激素信号（1）。绿色革命的一个关键部分，使作物产量增加了一倍以上，是开发新的矮秆品种，其中许多后来被发现在GA途径中有突变（2-4）。因此，了解GA的生长调节是进一步提高作物产量的主要目标。最近已经取得了相当大的进展，解剖GA行动的分子基础（参考文献1）;然而，尽管有这些进展，它仍然不清楚这种关键激素如何促进生长在细胞，组织或器官水平的组织。在PNAS中，Shani et al. (5)描述GA如何分布在模式植物拟南芥的根组织中。通过开发荧光标记的GA，作者能够证明这种关键的生长促进激素信号在特定的根组织和发育区域内积累。拟南芥主根具有简单的结构，沿着径向轴由表皮、皮层、内胚层、周鞘和中柱（维管）组织的同心层组成;沿沿着顶部-基部轴由空间上不同的分生组织、伸长和分化区组成（见图1示意图）。细胞在靠近根尖的分生区分裂;然后，在停止分裂并进入伸长区后，细胞经历快速扩增;然后细胞在进入分化区后最终停止生长。研究发现，GA生物合成或信号传导途径的突变组分导致根长度显著缩短（6，7），因为GA促进根分生组织中的细胞分裂（8，9）和伸长区中的细胞扩增（7，10）。在分子尺度上，GA通过触发生长抑制DELLA蛋白的降解来促进生长。GA可以通过协调DELLA蛋白在每个组织中的同时降解来促进拟南芥根的生长，或者，DELLA降解可能仅在一个或多个组织中需要。一些证据表明GA在组织和生长区之间分布不均匀。例如，根内皮层已被证明在GA调节根生长中特别重要：Ubeda Tomás等人。（8，10）报道，通过特异性表达DELLA的不可降解形式的组织，当内胚层细胞内的GA信号传导被阻止时，根生长被阻断。最近，在玉米叶（其具有与拟南芥根等同的发育区）中使用基于质谱（MS）的方法直接测量GA代谢物已经揭示，生物活性GA水平在所谓的过渡区中很高，在过渡区中细胞停止分裂并开始扩增（11）。然而，直到现在，直接确定GA信号在细胞水平上积累以控制器官生长的确切位置仍然有待解决。Shani等人(5)通过采用最先进的成像（而不是基于MS的）解决方案，能够准确地解决GA在根组织中积累的位置。通过使用可变长度的酰胺接头将荧光标签连接到GA 3和GA 4的四环二萜类结构的C6位置，作者能够回收几种保留生物活性的荧光GA替代物（称为GA 3-F1和GA 4-F1）。使用体外免疫共沉淀和酵母双杂交测定，还显示GA 3-F1和GA 4-F1促进GA受体GID 1与其DELLA靶标之间的相互作用。重要的是，没有分解产物的GA 3-F1和GA 4-F1与根孵育后检测，表明。
Gibberellins (GA) represent a key class of hormone signals that promote plant growth and development (1). A key part of the Green Revolution, which saw crop yields more than double, was the development of new dwarf varieties, many of which were later found to have mutations in the GA pathway (2–4). Thus, understanding GA’s growth regulation represents a prime target for further increasing crop production. Considerable progress has recently been made dissecting the molecular basis of GA action (reviewed in ref. 1); however, despite these advances, it remains unclear how this key hormone promotes growth at either the cellular, tissue, or organ levels of organization. In PNAS, Shani et al.(5) describe how GA is distributed within root tissues of the model plant Arabidopsis thaliana. By developing a fluorescent-labeled GA, the authors were able to demonstrate that this key growth-promoting hormone signal accumulates within a specific root tissue and developmental zone. The Arabidopsis primary root has a simple structure composed, along the radial axis, of concentric layers of epidermal, cortical, endodermal, pericycle, and stele (vascular) tissues; and along the apical-basal axis of spatially distinct meristem, elongation, and differentiation zones (see schematic in Fig. 1). Cells divide close to the root tip in the meristematic zone; then, after stopping dividing and entering the elongation zone, cells undergo rapid expansion; cells then eventually cease growth upon entering the differentiation zone. Studies have found that mutating components of the GA biosynthesis or signaling pathways results in a significantly shorter root length (6, 7) because of GA promoting cell division in the root meristem (8, 9) and cell expansion in the elongation zone (7, 10). At the molecular scale, GA promotes growth by triggering the degradation of the growth-repressing DELLA proteins. GA could promote Arabidopsis root growth by coordinating the simultaneous degradation of DELLA proteins in every tissue, or alternatively, DELLA degradation may only be required in one or more tissues. Several pieces of evidence suggest that GA is distributed unequally between tissues and growth zones. For example, the root endodermis has been shown to be particularly important in GA regulation of root growth: Ubeda Tomás et al.(8, 10) reported that by tissue specifically expressing a nondegradable form of DELLA, root growth was blocked when GA signaling was prevented within endodermal cells. Recently, direct measurements of GA metabolites using a mass spectrometry (MS)-based approach in the maize leaf (which has equivalent developmental zones to the Arabidopsis root) have revealed that bioactive GA levels are high in the so-called transition zone where cells cease to divide and start to expand (11). Nevertheless, directly determining exactly where the GA signal accumulated at a cellular level of resolution to control organ growth remained to be resolved until now. Shani et al.(5) are able to address exactly where GA accumulated in root tissues by adopting a state-of-the-art imaging (rather than MS-based) solution. By attaching a fluorescent tag using variable lengths of an acyl amide linker to the C6 position of the tetracyclic di-terpenoid structures of GA3 and GA4, the authors are able to recover several fluorescent GA-surrogates (termed GA3-Fl and GA4-Fl) that retained bioactivity. GA3-Fl and GA4-Fl were also shown to promote the interaction between the GA receptor GID1 and its DELLA target using in vitro coimmunoprecipitation and yeast two-hybrid assays. Importantly, no breakdown products of GA3-Fl and GA4-Fl were detected after incubation with roots, indicating …