MOLECULAR GENETICS OF AUXIN ACTION IN ARABIDOPSIS

植物激素生长素是植物生长发育的不同方面所必需的。我们已经证明，生长素需要泛素样蛋白RUB与一个或多个细胞蛋白结合。在拟南芥中，RUB激活酶AxR1-ECR1和RUB结合酶Rce1参与RUB接合。AxR1基因的隐性突变或表达显性-阴性版本的ECR1会导致生长素反应减弱。在植物、真菌和动物中，RUB与cullin家族的成员连接，包括酿酒酵母中的CDC53和拟南芥中的AtCUL1。我们的研究表明，摩擦修饰影响了cullin的功能，而不是其稳定性。以拟南芥为例，我们认为AtCUL1的摩擦修饰影响了SCFtiri的功能，SCFtiri是生长素反应所需的泛素蛋白质连接酶。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我们对生长素作用的研究。此外，至少存在两种分化的RUB蛋白。这两个分子在生长素反应中的功能将被确定。第二个目的是确认生长素反应需要摩擦修饰的AtCUL1。在拟南芥中至少还有另外两个库林蛋白，这些蛋白的功能将被研究。第三个目的是通过各种实验方法来确定摩擦修改对AtCUL1功能的影响。第四个目标是分离和鉴定SAR1和AXR4基因。遗传学研究表明，这两个基因都在AxR1-TIR1途径中发挥作用。在第五个也是最后一个特定目标中，我们将对几个新的AxR1突变抑制基因进行基因和表型鉴定。根据这些研究的结果，我们将分离和鉴定这些新基因中的一个或多个。我们期望这些研究的结果能为生长素的反应机制提供重要的新信息。此外，我们的研究将为所有真核生物中高度保守的RUB-共轭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.