Little is known about biochemical or signalling pathways in potato that are involved in resistance to pathogens, whether mediated by resistance genes or as a component of 'field' or 'durable' resistance. Moreover, there is even less information comparing resistance in leaf tissue with that in root. Knowledge from such comparisons could be crucial in developing broad-range plant disease resistance strategies. Research at the Scottish Crop Research Institute (SCRI) has focused on discovery of plant genes up-regulated during resistant and susceptible interactions between potato and the foliar pathogen Phytophthora infestans, the stem and tuber pathogen Erwinia carotovora and the root pathogens Globodera pallida and G. rostochiensis (potato cyst nematodes or PCN). These pathogens are amongst the most economically devastating for potato, the world's fourth major crop. Gene discovery at SCRI, through genetic mapping of key resistance-associated loci, and through transcriptional profiling of resistance pathways, is geared to meet the following objectives: to identify receptors responsible for triggering durable disease resistance, to identify common and distinct pathogen response pathways in root and leaf tissues, to compare resistance mechanisms in different pathosystems, to identify key, general, rapidly activated pathogen response promoters, and to characterise the functions of genes activated in resistance responses in potato. We also seek to answer fundamental questions about the pathogens themselves, such as: What genes are required for successful infection? What is the nature of avirulence genes? What are the molecular bases of host-specificity in these pathogens? To tackle these questions we have adopted genomics approaches. For P. infestans, a framework of integrated genetic, physical and transcriptional maps is being constructed to facilitate rapid discovery of genes involved in the interaction with the host plant. With potato cyst nematodes the focus has been on expressed sequences and defining their function through localisation and biochemical characterisation. More recently, RNAi is being developed to aid in defining function. In the case of Erwinia carotovora subsp. atroseptica, and the closely related E. chrysanthemi, full genome sequencing projects for these organisms are nearing completion, and resources have been developed for post-genomic analyses, including transcriptional and proteomic profiling and a transposon mutation grid to rapidly isolate mutants in any given gene.