The Role of START Lipid/Sterol Binding Domains in Homeodomain Transcription Factors of Plants

甾醇是一种不溶于水的小分子，在动物和植物的生长发育中起着至关重要的作用。植物分子生物学领域正在进行的研究揭示了甾醇衍生的油菜素内酯的重要性，这是迄今为止从植物中鉴定出的唯一类固醇激素。除油菜素内酯外，植物还含有多种甾醇化合物，其生物学功能尚不清楚。Schrick实验室的长期目标是鉴定和表征植物中假定的固醇信号通路的组成部分。候选的固醇结合蛋白包括一个同源结构域（HD）转录因子家族，它们具有甾体生成急性调节（StAR）相关脂质转移（START）脂质/固醇结合结构域。START结构域以哺乳动物胆固醇结合StAR蛋白命名，存在于真核生物的多种蛋白质中，但只在少数动物中进行了研究。引人注目的是，START结构域与HD dna结合基序的结合是植物所特有的。本项目提出了一个假说，即HD转录因子中的START结构域与脂质/固醇配体结合，这种相互作用控制着发育过程中的基因表达。来自拟南芥、玉米和水稻的HD-START家族的几个成员在细胞分化和/或表现出层特异性表达模式中起着至关重要的作用。以拟南芥分生系统层1 （ATML1）和GLABRA2 （GL2）基因为模型，本项目的目的是研究START结构域作为脂质/固醇结合基序的假设作用。潜在的配体将通过一种新的体内脂质/甾醇结合实验来鉴定，该实验利用酵母酿酒酵母。在该分析中，START结构域作为合成转录因子的一部分表达，该转录因子在响应配体结合时激活报告基因。该试验将用于测试脂质/甾醇化合物与拟南芥HD-START转录因子候选START结构域结合的化学文库，并用于选定START结构域的突变分析。该项目的完成将为植物START结构域在配体结合中的假定功能提供一个概念框架，可能揭示植物脂质/固醇代谢与细胞分化之间的联系。此外，这项工作将导致对HD-START转录因子在植物发育中的作用的理解取得重大进展，并将导致对脂质/固醇信号传导机制的重要见解。本研究将通过研究生和本科生的多学科教育产生更广泛的影响，从本研究中获得的信息将有助于改进植物源物质在生物技术中的实际应用。

Sterols are small water-insoluble molecules that play critical roles in growth and development of both animals and plants. Ongoing research in the field of plant molecular biology has revealed the importance of the sterol-derived brassinosteroids, which are the only steroid hormones identified from plants thus far. In addition to brassinosteroids, plants contain a wide variety of sterol compounds whose biological functions are not understood. The long-term goal of the Schrick lab is to identify and characterize the components of putative sterol signaling pathways in plants. Candidate sterol-binding proteins include a family of homeodomain (HD) transcription factors having Steroidogenic Acute Regulatory (StAR)-related lipid transfer (START) lipid/sterol-binding domains. START domains, named after the mammalian cholesterol-binding StAR protein, are found in a variety of proteins across the eukaryotes, but have been studied in only a few cases from animals. Strikingly, START domains in combination with the HD DNA-binding motif are unique to plants. This project addresses the hypothesis that the START domain found in HD transcription factors binds to lipid/sterol ligands and that this interaction controls gene expression during development. Several members of the HD-START family from Arabidopsis, maize, and rice, have crucial roles in cell differentiation and/or exhibit layer-specific expression patterns. Using the Arabidopsis thaliana Meristem Layer 1 (ATML1) and GLABRA2 (GL2) genes as models, the aim of this project will be to examine the putative role of START domains as lipid/sterol binding motifs. Potential ligands will be experimentally identified in a novel in vivo lipid/sterol-binding assay utilizing the yeast Saccharomyces cerevisiae. In the assay the START domain is expressed as part of a synthetic transcription factor that activates a reporter gene in response to ligand binding. This assay will be implemented to test a chemical library of lipid/sterol compounds for binding to candidate START domains from Arabidopsis HD-START transcription factors, and additionally will be used for mutational analysis of selected START domains. Completion of this project will provide a conceptual framework for the presumed function of plant START domains in ligand binding, potentially revealing a link between lipid/sterol metabolism and cell differentiation in plants. Moreover, this work will result in significant advances in understanding of the role of HD-START transcription factors in plant development, and will lead to important insights underlying lipid/sterol signaling mechanisms. This research will have broader impacts through multidisciplinary education of graduate students as well as undergraduates, and the information gained from this research will facilitate improvements in plant-derived substances for practical applications in biotechnology.