The interaction between the model plant Arabidopsis and the obligate biotroph Peronospora parasitica is being studied in order to isolate componenets of disease resistance signalling pathways. The recent cloning of RPP5, an Arabidopsis gene specifying resistance to P. parasitica, reveals striking structural similarity to several cloned R genes from other plant species, suggesting strong conservation of pathogen recognition and signalling mechanisms between plant species. Two novel resistance signalling genes, NDR1 and EDS1, were identified independently in Arabidopsis by mutational analysis. The EDS1 mutation abolisches resistance mediated by several RPP loci, including RPP5, and by RPS4 which controls resistance to a bacterial pathogen. In contrast, ndr1 suppresses the function of two other bacterial R loci, RPM1 and PRS2, which are unaffected by eds1, and several RPP loci. It is possible, therefore, that these mutations define two distinct R gene-mediated signalling pathways, although a direct comparaison of their effects on the same spectrum of RPP genes has not yet been made. The proposed project will (i) further characterize the phenotype of eds1 with selected RPP loci, using six available mutant alleles (ii) compare the effects of the eds1 and ndr1 mutations on the same spectrum of selected RPP loci using intercrossed F3 families (iii) examine the effects of eds1 on the production of implicated resistance components, salicylic acid, camalexin and the transcription of defence-related genes under different pathogen challenged conditions (iv) sequence the defective eds1 alleles upon the cloning of the EDS1 gene, for which two putative transposon tagged alleles have recently been isolated. It is anticipated that dissection of resistance signalling pathways in Arabidopsis will have relevance to the understanding of mechanisms operating in less tractable crop plants.
The technical resources devoted to Arabidopsis and molecular genetic tools available, combined with a well characterized plant-pathogen interaction, provide an imparalleled opportunity to expore the molecular basis to disease resistance. This should have a major impact on the design of new crop protection strategies. The research area is new to me, intelectually challanging, and will traing me in a wide range of molecular and biochemical techniques.