Plants within the Brassicaceae are generally unable to form functional symbiotic associations with nitrogen fixing bacteria or mycorrhizal fungi in the soil. Nonetheless, many of the genes involved in these evolutionarily related symbiosis pathways (SYM genes) have homologues in Brassicas. One hypothesis is that these genes function in other plant-microbe interaction pathways such as pathogen recognition and response. This project explores the evolution and function of seven SYM-like genes in Brassicas that are required for the early stages of rhizobia/mycorrhizae perception and signal transduction in legume species and which have homologues in rice and Arabidopsis. The expression of these genes in various plant tissues in response to microbial elicitors and both beneficial and pathogenic microbes is being analysed using quantitative real-time PCR. Functional analyses of these proteins using transgenic approaches, Arabidopsis mutants and B. rapa TILLING mutants are being undertaken. By associating SYM gene structure, organisation, expression and conservation with functional analyses across such a diverse range of Brassica species, functionally important protein motifs will be revealed and allelic variants analysed in the context of natural selection pressure and crop domestication. This has relevance for the discovery and functional analysis of new genetic loci and alleles involved in microbial recognition and pathogen resistance, with application for crop protection and breeding.