Investigating Roles for Nodulation-Like Genes in the Non-Nodulating Brassicaceae

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 SYMBIOSIS (SYM) genes common to these evolutionarily related symbioses have homologues in rice, Arabidopsis and the recently sequenced Brassica genomes. These include the transcription factor genes NSP1, NSP2 and NIN required for the early stages of rhizobia/mycorrhiza perception and signal transduction in legume species. One hypothesis is that these genes function in other plant-microbe interaction pathways in Brassicas, such as pathogen recognition and response. This project explores the evolution and function of SYM genes within a diverse selection of Brassicaceae.

Similarly to their legume counterparts, the expression of these genes is upregulated in root tissues of the important Brassica crop B. napus (rapeseed) and in response to the presence of microbial elicitors.  T-DNA insertion and TILLING mutants for these genes in Arabidopsis and B. rapa are being assayed for perturbed pathogen and symbiont interactions. Functional analyses of these proteins using transgenic approaches will ascertain the putative function of these genes in the Brassicaceae, with relevance for pathogen response, and will determine if they retain SYM function in model legume species. By associating SYM gene structure, organisation and expression with functional analyses across such, 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.