Functional Analysis of RGA, a Negative Regulator of Gibberellin Signaling in Arabidopsis

生物活性赤霉素（GAs）是一类植物生长激素，控制种子萌发、茎伸长、花和果实发育等多种过程。 虽然GAs对植物生长的生理效应有很好的记录，但对这种激素信号如何导致生物化学和形态学变化知之甚少。 近年来，利用生物化学和遗传学方法研究发现了高等植物GA信号转导途径中的三个负调控因子：RGA、GAI和SPY。 编码这些蛋白质的基因在不同物种中高度保守。 RGA和GAI都可能作为转录调节因子发挥作用，而SPY可能是一种通过连接糖残基来修饰其他蛋白质的酶。 目前的工作假设是，SPY可能会修改和激活RGA和GAI抑制GA信号转导的情况下（或低）GA信号。 因此，GA信号传导的基础状态是抑制性的，并且GA信号通过抑制负调节剂来解除抑制该途径。本研究旨在阐明RGA在模式植物拟南芥中调控GA信号转导的生化功能。 具体目的是检查RGA的活性是否通过蛋白质修饰和/或通过改变其亚细胞定位来调节，并鉴定与RGA相互作用的细胞蛋白。 这些研究将揭示GA控制植物生长发育的分子机制。 这些知识还将有助于制定更有效的战略，以改善未来的农作物。

Bioactive gibberellins (GAs) are a class of plant growth hormones, which control diverse processes including seed germination, stem elongation, flower and fruit development. Although the physiological effects of GAs on plant growth are well documented, much less is known about how this hormone signal leads to biochemical and morphological changes. Recent studies using biochemical and genetic approaches have identified three negative regulators (RGA, GAI and SPY) in GA signal transduction pathway in higher plant. The genes encoding these proteins are highly conserved in different species. Both RGA and GAI are likely to function as transcription regulators, whereas SPY is probably an enzyme that modifies other proteins by attaching sugar residues. The current working hypothesis is that SPY may modify and activate RGA and GAI to repress GA signal transduction in the absence of (or in low) GA signal. The basal state of GA signaling is therefore to be repressive, and the GA signal de-represses the pathway by inhibiting the negative regulators. This proposal focuses on elucidating the biochemical function of RGA in regulating GA signal transduction in the model plant Arabidopsis. The specific aims are to examine whether the activity of RGA is modulated by protein modification and/or by alteration of its subcellular localization, and to identify cellular protein(s) that interact with RGA. These studies will shed lights on the molecular mechanisms by which GA controls plant growth and development. This knowledge will also facilitate more effective strategies to improve agricultural crops in the future.