Characterization of Negative Regulators of NPR1-Mediated Systemic Acquired Resistance

Duke University, Durham NC

Investigators

Abstract

The long-term goal of this research is to use Arabidopsis thaliana as a model system to determine the signaling events leading to systemic acquired resistance (SAR). SAR is a secondary pathogen resistance which can be induced after a local infection. SAR is broad-spectrum and long-lasting. Through genetic screens, NPR1 has been identified as a key positive regulator of SAR; mutants of the NPR1 gene are nonresponsive to SAR induction. NPR1 encodes a novel protein with functionally important protein-protein interacting domains, the BTB domain and the ankyrin-repeat domain. Recent data show that nuclear localization of NPR1 is essential for its function. In the nucleus, NPR1 may affect the activities of the TGA subclass of bZIP transcription factors as well as the WRKY transcription factors, which have been implicated as transcriptional activators and repressors of pathogenesis-related (PR) genes, respectively. A genetic screen for suppressors of npr1 has led to identification of sni1, a mutation that restores systemic induction of PR genes in npr1. The wild-type SNI1 is believed to be a negative regulator of SAR whose inactivation requires the function of NPR1. It is hypothesized that NPR1 induces SAR by activating the TGA transcription activators and inactivating WRKY transcription repressors, and relieving the negative control of SNI1. In this project, molecular genetic and biochemical experiments are designed to (1) determine the functional significance of the interaction between NPR1 and WRKY transcription factors in SAR; (2) determine the mechanism by which SNI1 functions as a negative regulator of SAR; and (3) identify components in the NPR1-complex. Because NPR1, SNI1, and WRKY transcription factors are either novel or plant-specific proteins, characterization of these components may unveil new mechanisms of signal transduction. Understanding molecular mechanisms of disease resistance in plants will lead to the development of technology in enhancing plants' innate defense to control infection. Such technology has the potential to reduce the use of hazardous pesticides without using non-plant genes. Therefore, the study of plant-microbe interactions is of interest to advancement of basic science as well as to protection of the environment and improvement of human life.