Molecular Genetics of Auxin Action

描述(申请人提供)：植物激素生长素参与植物生长和发育的几乎所有方面。在上一次授予期间，我们证明了生长素通过刺激称为AUX/IAA蛋白的转录抑制蛋白家族的降解来发挥作用，这一过程需要泛素蛋白连接酶SCFTIR1和相关的SCF。在我们最近的研究中，我们已经表明生长素直接与SCFTIR1或一种密切相关的蛋白质相互作用。我们认为生长素结合促进了SCFTIR1与其底物AUX/IAA蛋白之间的相互作用。这是一种新的激素作用和SCF调节机制。目前的提案有三个具体目标。第一个是研究生长素对AUX/IAA降解的调节。将确定AUX/IAA识别所需的TIR1区域。将进行生化实验，以鉴定和表征介导AUX/IAA识别的蛋白质，特别是确定生长素作用的直接靶标。此外，AUX/IAA蛋白的结构将与我的同事L.Chen博士合作确定。在第二个目标中，我们将描述拟南芥根转录组的特征。这一目标的目的是确定AUX/IAA调节的下游靶点，并比较不同生长素生长反应的细胞类型中生长素调节的转录。一些候选的生长素反应基因已经被识别出来，这些基因将被鉴定。在第三个目标中，我们将对生长素反应不足的新突变体进行新的遗传筛选。我们的重点将放在胚胎和根发育有严重缺陷的突变株上，这些缺陷在以前的筛查中不太可能恢复。我们希望我们的实验能为生长素的作用机制提供新的基本见解。此外，我们的研究表明，生长素通过一种新的机制发挥作用，包括直接与泛素蛋白连接酶结合。这些结果将对包括人类在内的不同物种的蛋白质降解研究产生重大影响。

DESCRIPTION (provided by applicant): The plant hormone auxin is involved in virtually all aspects of plant growth and development. During the last grant period we demonstrated that auxin acts by stimulating the degradation of a family of transcriptional repressers called the AUX/IAA proteins, a process that requires the ubiquitin protein ligase SCFTIR1 and related SCFs. In our most recent studies we have shown that auxin interacts directly with SCFTIR1 or a closely associated protein. We propose that auxin binding promotes the interaction between SCFTIR1 and its' substrates, the AUX/IAA proteins. This is a novel mechanism of hormone action and SCF regulation. The current proposal has three specific aims. The first is to investigate auxin regulation of AUX/IAA degradation. The region of TIR1 that is required for AUX/IAA recognition will be identified. Biochemical experiments will be conducted to identify and characterize proteins that mediate AUX/IAA recognition and in particular the direct target of auxin action will be defined. Further, the structure of the AUX/IAA proteins will be determined in collaboration with my colleague, Dr. L. Chen. In the second aim we will characterize the Arabidopsis root transcriptome. The goals of this aim are to identify downstream targets of AUX/IAA regulation and to compare and contrast auxin regulated transcription in cell types with different auxin growth responses. A number of candidate auxin-response genes have been identified and these will be characterized. In the third aim, we will conduct novel genetic screens for new mutants deficient in auxin response. Our emphasis will be on mutants with severe defects in embryo and root development that are unlikely to be recovered in previous screens. We expect our experiments to provide fundamental new insight into the mechanism of auxin action. Further, our studies indicate that auxin acts through a novel mechanism that involves direct binding to a ubiquitin protein ligase. These results will have significant impact on studies of protein degradation in diverse species including humans.