Molecular mechanisms of auxin response in Arabidopsis

描述（由申请人提供）：激素生长素几乎调节植物生长发育的各个方面。对拟南芥的遗传和分子研究已经确定SCFTIR1泛素连接酶复合物是生长素反应的积极调节因子。最近的研究表明，生长素促进了scftir1介导的Aux/IAA蛋白的泛素化，这是一个大的转录调节家族，负向调节生长素的反应。随后蛋白酶体介导的Aux/IAAs降解会抑制生长素反应通路，导致生长发育的变化。我们已经证明，在粗幼苗提取物中，Aux/IAA蛋白与SCFTIR1复合物发生物理相互作用。生长素通过一种未知的机制将这些因子靶向到SCFTIR1泛素连接酶，从而促进Aux/IAA降解。阐明生长素如何调节这种相互作用将为研究SCFTIR1泛素连接酶上游生长素反应途径的信号事件提供重要信息。本研究的长期目标是了解生长素调控植物生长发育的分子机制。生长素作用机制的确定将为调控生长素对农业和园艺的影响提供新的工具。此外，由于scf介导的泛素化是高度保守的，这些研究将有助于我们理解所有真核生物中这种细胞调节模式。本建议的具体目标包括：1)阐明Aux/IAA转录调控因子与SCFTIR1泛素连接酶复合物之间蛋白-蛋白相互作用的性质和调控；2)一类新的拟南芥生长素反应缺陷突变体的遗传和分子分析；3) AtCUL1 SCF亚基突变衍生物的分子特征；4)探讨AXR2 Aux/IAA蛋白与COP9信号体亚基CSN5相互作用的生物学意义。

DESCRIPTION (provided by applicant): The hormone auxin regulates virtually every aspect of plant growth and development. Genetic and molecular studies with Arabidopsis have defined the SCFTIR1 ubiquitin-ligase complex as a positive regulator of auxin response. Recent findings indicate that auxin promotes SCFTIR1-mediated ubiquitination of the Aux/IAA proteins, a large family of transcriptional regulators which negatively regulate auxin response. The subsequent proteasome-mediated degradation of the Aux/IAAs derepresses the auxin response pathway resulting in changes in growth and development. We have shown that Aux/IAA proteins physically interact with the SCFTIR1 complex in crude seedling extracts. Auxin promotes Aux/IAA degradation by targeting these factors to the SCFTIR1 ubiquitin-ligase by an undetermined mechanism. Elucidation of how auxin regulates this interaction will provide important information into the signaling events of the auxin response pathway upstream of the SCFTIR1 ubiquitin-ligase. The long-term goal of the proposed research is to understand the molecular mechanisms underlying auxin regulation of plant growth and development. The identification of the mechanisms underlying auxin action will provide new tools for modulating auxin response for agricultural and horticultural benefit. Further, since SCF-mediated ubiquitination is highly conserved, these studies will contribute toward our understanding of this mode of cellular regulation in all eukaryotes. The specific objectives of this proposal include; 1) elucidation of the nature and regulation of protein-protein interactions between the Aux/IAA transcriptional regulators and the SCFTIR1 ubiquitin-ligase complex; 2) the genetic and molecular analysis of a new class of Arabidopsis mutants defective in auxin response; 3) the molecular characterization of a mutant derivative of the AtCUL1 SCF subunit; and 4) investigate the biological significance of the interaction between the AXR2 Aux/IAA protein and the COP9 signalosome subunit CSN5.