Role of the Pti4 and Pti5 Transcription Factors in Pto-Mediated Defense Gene Activation and Disease Resistance

这个项目的重点是在植物识别细菌病原体后发生的分子事件，这些事件导致防御相关基因表达增加。为了研究这些事件，研究了番茄对由丁香假单胞菌引起的细菌性斑点病的抗性。对番茄进行了研究。当番茄植株表达PTO抗性基因而细菌表达avrPto无毒基因时，对斑点病的抗性就以基因对基因的方式发生。PTO基因的产物是一种丝氨酸苏氨酸激酶，对AvrPto蛋白的识别导致许多“病程相关”(PR)基因的快速诱导(以及其他防御反应)。在之前的NSF支持下，两个转录因子Pti4和Pti5被鉴定出来，它们与PTO激酶相互作用，并与存在于许多PR基因启动子中的DNA调节元件结合。Pti4和Pti5基因在番茄叶片中被假单胞菌感染诱导表达，并且在假单胞菌与番茄相互作用过程中Pti5的表达进一步增加。此外，Pti4蛋白被PTO激酶磷酸化，从而增强了它与GCC盒的结合。在植物中过表达Pti4或Pti5会导致某些PR基因的结构性表达。因此，Pti4和Pti5似乎定义了抗病基因PTO和PR基因激活之间的分子联系。将鉴定被PTO磷酸化的Pti4的氨基酸，并确定这种磷酸化在Pti4活性中的作用。在过量表达Pti4和Pti5的番茄和拟南芥植物中发生的全基因组基因表达变化将被阐明，这些植物将被测试抗病能力的变化。为了了解PTO介导的Pti5的诱导，我们将确定该基因的假单胞菌反应启动子元件，并鉴定它们的同源转录因子。最后，将发现Pti4介导PR基因表达所需的新的植物基因位点。这些研究将阐明与植物抗病相关的转录因子调控的关键步骤。

This project focuses on the molecular events that occur after a plant recognizes a bacterial pathogen and which result in increased expression of defense-related genes. To investigate these events, resistance in tomato to bacterial speck disease caused by Pseudomonas syringae pv. tomato is studied. Resistance to speck disease occurs in a "gene-for-gene" fashion when the tomato plant expresses the Pto resistance gene and the bacterium expresses the avrPto avirulence gene. Recognition of AvrPto protein by the product of the Pto gene, a serine-threonine kinase, leads to the rapid induction of many "pathogenesis-related" (PR) genes (among other defense responses). With previous NSF support, two transcription factors, Pti4 and Pti5, were identified that interact with the Pto kinase and which bind a DNA regulatory element present in the promoter of many PR genes. The Pti4 and Pti5 genes are induced in tomato leaves by Pseudomonas infection, and Pti5 expression is further increased during a Pseudomonas-tomato interaction involving AvrPto-Pto. Furthermore, the Pti4 protein is phosphorylated by the Pto kinase and its binding to the GCC box is thereby enhanced. Overexpression of Pti4 or Pti5 in plants leads to constitutive expression of certain PR genes. Thus, Pti4 and Pti5 appear to define a molecular link between the disease resistance gene Pto and activation of PR genes. Amino acids of Pti4 that are phosphorylated by Pto will be identified and the role of this phosphorylation in Pti4 activity will be determined. Genome-wide gene expression changes that occur in tomato and Arabidopsis plants overexpressing Pti4 and Pti5 will be elucidated, and these plants will be tested for alterations in disease resistance. To understand the Pto-mediated induction of Pti5, the Pseudomonas-responsive promoter elements of this gene will be determined and their cognate transcription factors will be identified. Finally, new plant loci that are required for Pti4-mediated expression of PR genes will be discovered. These studies will elucidate key steps in the regulation of transcription factors associated with plant disease resistance.