Novel Components of Brassinosteroid Signaling

油菜素类固醇是一种植物激素，在协调生长和发育方面发挥着重要作用。拟南芥基因油菜素类固醇不敏感1(BRI1)编码一种受体样蛋白激酶(RLK)，它是油菜素类固醇介导的信号转导的关键成分。利用激活标签技术，我们发现了一个可以抑制突变的BRI1等位基因生长缺陷的基因。这种BRI1抑制子BRS1被预测编码一种分泌型丝氨酸羧基肽酶。BRS1的高表达抑制了两个在胞外区发生突变的BRI1等位基因，但不抑制激酶域的突变。遗传学和生理学数据有力地表明，BRS1调节油菜素类固醇信号的早期步骤。在许多信号转导途径中，蛋白水解物处理在调节信号感知和转导方面起着重要作用。我们假设BRS1参与了BRI1信号通路中的蛋白降解处理步骤。为了验证这一假设，我们建议对BRS1进行详细的表征，包括它的细胞和亚细胞定位，以及它的酶活性分析。此外，BRS1还是一个基因家族的成员。为了研究BRS1和类似BRS1的基因在BRI1和其他RLK信号通路中的可能参与，我们将使用遗传学方法来研究它们的功能。这些研究将有助于我们理解油菜素类固醇信号和其他RLK介导的控制植物生长发育的过程。

Brassinosteroids are plant hormones that perform a fundamental role in coordinating growth and development. The Arabidopsis gene, Brassinosteroid Insensitive 1 (BRI1), encodes a receptor-like protein kinase (RLK), which is a critical component in brassinosteroid-mediated signaling. Using activation tagging, we identified a gene can suppress the growth defects of a mutant bri1 allele. This bri1 suppressor, BRS1, is predicted to encode a secreted serine carboxypeptidase. Elevated expression of BRS1 suppresses two bri1 alleles that have mutations in their extracellular domain, but not a kinase domain mutation. Genetic and physiological data strongly suggest BRS1 regulates an early step in brassinosteroid signaling. In many signal transduction pathways proteolytic processing plays an important role in regulating signal perception and transduction. We hypothesize that BRS1 is involved in a proteolytic processing step in the BRI1 signaling pathway. To test this hypothesis, we propose to undertake a detailed characterization of BRS1, including its cellular and subcellular localization, and analysis of its enzymatic activity. In addition, BRS1 is a member of a gene family. To examine a possible involvement of BRS1 and the BRS1-like genes in BRI1 and other RLK signaling pathways, we will use genetic approaches to investigate their function. These studies will contribute to our understanding of brassinosteroid signaling and other RLK mediated processes that control growth and development in plants.