MOLECULAR GENETICS OF AUXIN ACTION IN ARABIDOPSIS

植物生长素是植物生长和发育的各个方面所必需的。我们已经证明，生长素需要泛素样蛋白 RUB 与一种或多种细胞蛋白结合。在拟南芥中，RUB 激活酶 AXR1-ECR1 和 RUB 结合酶 RCE1 参与 RUB 结合。 AXR1 基因的隐性突变或 ECR1 显性失活版本的表达会导致生长素反应减弱。在植物、真菌和动物中，RUB 与 cullin 蛋白家族的成员缀合，包括酿酒酵母中的 Cdc53 和拟南芥中的 AtCUL1。我们的研究表明 RUB 修饰影响 cullin 的功能而不是其稳定性。就拟南芥而言，我们提出 AtCUL1 的 RUB 修饰会影响 SCFtiri 的功能，SCFtiri 是生长素反应所需的泛素蛋白连接酶。在这个项目中，我们将通过研究这些异构体在体外和体内的功能来继续研究生长素的作用。此外，至少有两种不同的RUB蛋白。这两个分子在生长素反应中的功能将被确定。第二个目的是确认 RUB 修饰的 AtCUL1 是生长素反应所必需的。拟南芥中至少还有两种额外的 cullin，这些蛋白质的功能将被研究。第三个目标是使用各种实验方法确定 RUB 修饰对 AtCUL1 功能的影响。第四个目标是分离和表征 SAR1 和 AXR4 基因。遗传学研究表明这两个基因都在 AXR1-TIR1 通路中发挥作用。在第五个也是最后一个具体目标中，我们将对 axr1 突变的几种新型抑制因子进行遗传和表型表征。根据这些研究的结果，我们将分离和表征这些新基因中的一个或多个。我们期望这些研究结果能够提供有关生长素反应机制的重要新信息。此外，我们的研究将为所有真核生物中高度保守的 RUB 缀合途径的功能提供新的见解。

The plant hormone auxin is required for diverse aspects of plant growth and development. We have shown that auxin is requires conjunction of the ubiquitin-like protein RUB to one or more cellular proteins. In Arabidopsis, the RUB-activation enzyme AXR1-ECR1 and the RUB- conjugating enzyme RCE1 participate in RUB conjugation. Recessive mutations in the AXR1 gene or expression of a dominant-negative version of ECR1, result in reduced auxin response. In plants, fungi and animals, RUB is conjugated to members of the cullin family of proteins, including Cdc53 in S. cerevisiae and AtCUL1 in Arabidopsis. Our studies indicate that RUB modification affects the function of the cullin rather that its stability. In the case of Arabidopsis, we propose the RUB-modification of AtCUL1 affects the function of SCFtiri, a ubiquitin-protein ligase required for auxin response. In this project we will continue our studies of auxin action by investigating the function of these isoforms both in vitro and in vivo. In addition, there are at least two divergent RUB proteins. The function of these two molecules in auxin response will be determined. The second aim is to confirm that RUB-modified AtCUL1 is required for auxin response. There are at least two additional cullins in Arabidopsis and the functions of these proteins will be investigated. The third aim is to determine the effects of RUB-modification on AtCUL1 function using a variety of experimental approaches. The fourth aim is to isolate and characterize the SAR1 and AXR4 genes. Genetic studies indicate that both of these genes function in the AXR1-TIR1 pathway. In the fifth and last specific aim we will conduct the genetic and phenotype characterization of several novel suppressors of the axr1 mutation. Based on the results of these studies we will isolate and characterize one or more of these new genes. We expect the results of these studies to provide important new information on the mechanism of auxin response. In addition, our studies will provide new insight into the function of the highly conserved RUB- conjugated pathway in all eukaryote.