Molecular Mechanisms of Brassinosteroid Action

类甾醇（BRs）是植物界重要的促生长天然产物，在花粉、种子和幼嫩营养组织中含量很低。私家侦探研究小组已经在拟南芥中发现了一个BR不敏感突变体（bri 1），它赋予了严重的多效性表型效应，抑制了植物的发育。BRI 1已被其他人证明编码膜结合的富含亮氨酸的重复序列Ser/Thr受体激酶。在动物中，肽类的转化生长因子-b（TGF-b）家族通过受体激酶起作用以显著影响涉及动物发育和成体体内平衡的若干途径。TGF-β受体相互作用蛋白（TRIP-1）是TGF-β II型受体激酶的细胞内底物，其在TGF-β信号传导中起重要作用。TRIP-1是一种WD重复蛋白，在动物、酵母和植物中也具有作为真核翻译起始因子eIF 3的必需亚基的双重作用，从而揭示了发育信号传导途径和蛋白质翻译控制之间的推定联系。私家侦探最近发现，TRIP-1同源物在植物中的转录水平在多种条件下受到BR处理的调节，并且反义TRIP-1植物表现出广泛的发育缺陷，包括一些类似于BR缺陷和BR不敏感突变体的表型。此外，重组BRI 1激酶结构域在体外磷酸化重组TRIP-1。这些发现表明TRIP-1可能介导了BR调节植物生长和发育的一些分子机制。私家侦探将通过执行以下两个目标来检验这一假设：目标1：将在各种条件下监测野生型和BR突变体中的TRIP-1蛋白水平，并将检查BR对翻译起始的影响。TRIP-1蛋白可能的核定位，除了它在eIF 3复合物中的作用，也将进行研究。目标二：免疫沉淀，然后质谱将被用来确定在体内磷酸化位点的TRIP-1和他们的依赖于一个活跃的BRI 1受体激酶。该项目将增加我们对BR信号转导的理解，以及这种激素在控制植物生长和发育中的作用。鉴于BR在整个植物界都有发现，对BR作用的分子机制的更深入了解可能对产生具有改变的生长特性的作物植物产生实际影响。

Brassinosteroids (BRs) are essential growth-promoting natural products found at low levels in pollen, seeds and young vegetative tissues throughout the plant kingdom. The P.I.'s group has identified a BR-insensitive mutant in Arabidopsis thaliana (bri1) that confers severe pleiotropic phenotypic effects inhibiting plant development. BRI1 has been shown by others to encode a membrane-bound leucine-rich repeat Ser/Thr receptor kinase. In animals, the Transforming Growth Factor-b (TGF-b) family of peptides, acts via receptor kinases to prominently impact several pathways involved in animal development and adult homeostasis. TGF-b Receptor Interacting Protein (TRIP-1) is an intracellular substrate of the TGF-b Type II receptor kinase that plays an important role in TGF-b signaling. TRIP-1 is a WD-repeat protein that also has a dual role as an essential subunit of the eukaryotic translation initiation factor eIF3 in animals, yeast and plants, thereby revealing a putative link between a developmental signaling pathway and the control of protein translation. The P.I.'s group recently found that transcript levels of TRIP-1 homologs in plants are regulated by BR treatment under a variety of conditions, and that antisense TRIP-1 plants exhibited a broad range of developmental defects including some that resemble the phenotype of BR-deficient and -insensitive mutants. Furthermore, recombinant BRI1 kinase domain phosphorylates recombinant TRIP-1 in vitro. These findings suggest that TRIP-1 may mediate some of the molecular mechanisms underlying the regulation of plant growth and development by BRs. The P.I. will test this hypothesis by performing the following two objectives: OBJECTIVE 1: TRIP-1 protein levels will be monitored under a variety of conditions, in both wild-type and BR mutants, and the effect of BR on translation initiation will be examined. The possible nuclear localization of TRIP-1 protein, in addition to its role in the eIF3 complex, will also be studied. OBJECTIVE 2: Immunoprecipitation followed by mass spectrometry will be used to identify in vivo phosphorylation sites of TRIP-1 and their dependence on an active BRI1 receptor kinase. This project should increase our understanding of BR signal transduction and the role that this hormone plays in controlling plant growth and development. Given that BRs are found throughout the plant kingdom, greater understanding of the molecular mechanisms of BR action could have practical impact on generating crop plants with altered growth properties.