Molecular Mechanisms of Brassinosteroid Action

9420016 Clouse β-inosteroids（BRS）是广泛存在的植物化合物，其结构与动物类固醇激素相似。 BRS具有许多生理作用，包括增强细胞伸长，但人们对这些植物生长调节剂的作用机制知之甚少。 一个综合的方法被用来调查一些生理和分子参数与BR促进茎组织伸长。 从BR处理的大豆（Glycine max L）上胚轴mRNA的cDNA文库中，克隆了在处理的两小时内主要由BRS调节的基因（BRU 1）。 BRU 1转录水平不增加微摩尔浓度的生长素，细胞分裂素，阿坝或BA 3，和BRU 1表达是最高的茎组织。 BRS引起Instron测量的塑性延展性的显著增加，表明它们可能部分地通过改变细胞壁的机械性质（壁松弛）来促进伸长。 BRU 1表达的增加与管壁松动的动力学密切相关。 这表明BRU 1蛋白在BR刺激的伸长中可能起作用。 本项目的目的是验证这一假设，并进一步研究植物类固醇对基因表达的调控。 尽管BRS对植物具有明显的促生长作用，并与其他生长调节剂相互作用，但对BRS作用的分子机制知之甚少。 了解BR活性对基础发育生物学和农业实践具有重要意义。 细胞壁在伸长过程中松弛的精确生化机制仍然是难以捉摸的。 完成拟议的实验可能会增加我们的知识的分子事件控制茎伸长。 BRS调节的BRU 1 mRNA水平增加的拟议研究应该增加我们的知识转录后机制，事实上，将是第一个详细的研究植物类固醇的基因调控机制。 BRU 1和其他BRS调节基因的分析也可能对具有改变的生长特性的转基因作物植物的发育具有未来的影响。

9420016 Clouse Brassinosteroids (BRS) are widely occurring plant compounds with structural similarity to animal steroid hormones. BRS have numerous physiological effects, including enhanced cell elongation, but little is known about the mechanism of action of these plant growth regulators. An integrative approach was used to investigate a number of physiological and molecular parameters associated with BR-promoted elongation of stem tissue. From a cDNA library of BR- treated soybean (Glycine max L) epicotyl mRNA, a gene (BRU1) was cloned which is regulated primarily by BRS within two hours of treatment. The BRU1 transcript levels are not increased by micromolar concentrations of auxins, cytokinins, ABA or BA3, and BRU1 expression is highest in stem tissue. BRS caused a marked increase in Instron- measured plastic extensibility, suggesting that they may promote elongation in part by altering mechanical properties of the cell wall (wall loosening). The kinetics of wall- loosening closely followed the increase in BRU1 expresssion. This suggests a possible role for the BRU1 protein in BR- stimulated elongation. The objective of this project is to test this hypothesis and to further examine the regulation of gene expression by plant steroids. Despite the obvious growth-promoting effects of BRS on plants and its demonstrated interactions with other growth regulators, little is known about the molecular mechanisms of BRS action. Understanding BR activity has great potential importance in basic developmental biology and practical agriculture. The precise biochemical mechanisms of wall loosening during elongation remain elusive. The completion of the proposed experiments may increase our knowledge of the molecular events controlling stem elongation. The proposed studies on BRS-regulated increases in BRU1 mRNA levels should add to our knowledge of posttranscriptional mechanisms and will, in fact, be the first detailed study of the mechanisms of gene regulat ion by plant steroids. The analysis of BRU1, and other BRS- regulated genes may also have future impact on development of transgenic crop plants with altered growth properties.