Novel Components of Brassinosteroid Signaling

油菜素内酯是植物激素，在协调生长发育中起着重要作用。拟南芥基因brassinosteroids Insensitive 1 （BRI1）编码一种受体样蛋白激酶（receptor-like protein kinase， RLK），这是油菜素类固醇介导的信号传导的关键成分。利用激活标记，我们发现了一个基因可以抑制突变bri1等位基因的生长缺陷。这个bri1抑制因子，BRS1，被预测编码分泌丝氨酸羧肽酶。BRS1的表达升高会抑制两个细胞外结构域突变的bri1等位基因，但不会抑制激酶结构域突变。遗传和生理数据强烈表明，BRS1调控了油菜素内酯信号传导的早期阶段。在许多信号转导途径中，蛋白水解加工在调节信号感知和转导中起着重要作用。我们假设BRS1参与了BRI1信号通路中的一个蛋白水解加工步骤。为了验证这一假设，我们建议对BRS1进行详细的表征，包括其细胞和亚细胞定位，并分析其酶活性。此外，BRS1是一个基因家族的成员。为了研究BRS1和BRS1样基因可能参与BRI1和其他RLK信号通路，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了解油菜素内酯信号和其他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.