Plants employ an array of distinct inducible defense responses to prevent infection and to recover from disease. While a few of the pathways that regulate these defenses are known, such as systemic acquired resistance (SAR), other critically important systems have eluded discovery. The proposed research is aimed at elucidating a novel form of SAR-independent resistance (SIR) expressed in Arabidopsis son1 (suppressor of nim1-1) mutants, and at defining and testing genes whose expression is associated with SIR. Two of the three objectives are focused on study of the son1 mutant phenotype and on the SON1 gene product, which was recently described (Kim and Delaney, 2002a). Because son1 plants express a novel form of resistance, it is essential that the resistance phenotype be fully described. Therefore, the defense signal transduction pathway requirements for son1-mediated resistance will be determined using double mutant analysis, the range of pathogen types susceptible to this resistance assessed, and the interactions between SAR and son1-mediated resistance evaluated (Objective 1). Investigations under Objective 2 will examine the SON1 protein itself, whose structure suggests it may be a component of an ubiquitin ligase complex that targets proteins for destruction. To assess whether SON1 plays this role, tests will be performed to determine whether SON1 interacts with core components of the ubiquitin ligase complex. Other work will seek to identify proteins targeted by SON1 that are hypothesized to act as positive regulators of SIR. The third objective of the project is to identify genes whose expression is altered in two genotypes of plants that express SIR; -son1 mutants and transgenic plants that were developed to overexpress the TGA5 transcription factor that interacts with the SAR-regulator NIM1 (Kim and Delaney, 2002b). The transcriptional profiles of son1 and TGA5-accumulating plants will be analyzed using oligonucleotide-based microarrays that include nearly all the Arabidopsis genes. By comparing gene expression in the two independently derived SIR-activated plants, the genes common to each will be evident. Some SIR-associated genes will be subjected to functional analysis to determine their role in SIR. The research described will yield important information on SIR expressed in son1 plants, provide insight into the regulation of SIR by SON1, provide molecular markers associated with SAR-independent resistance, and provide information that may lead to development of novel forms of disease control in crop plants.
The research described has a number of broader impacts outside of its biological aspects. These include: thorough training of undergraduate and graduate students and a postdoctoral fellow, broadening participation in research of underrepresented groups, enhancing the infrastructure for research through the sharing of transcriptional profile data generated by this project; and the broad dissemination of knowledge through presentations at conferences by undergraduate, graduate and postdoctoral personnel. The research can also be of general benefit to society by providing understanding of novel pathways that will enable creation of highly disease resistant crops, thus improving the economics of food production, and reducing the environmental impact and health consequences of currently used chemical disease control agents.
