Using Virulence Mutants to Identify Avr Genes in the wheat stem rust fungus, Puccinia graminis f. sp. tritici. [Meeting Abstract]

Rust fungi are biotrophic pathogens that depend on living host cells for their growth and form specialised haustoria structures during infection that serve as nutrient uptake sites as well as delivering effector proteins to the host cell. We have been investigating the molecular basis of rust infection and immunity using Melampsora lini (flax rust) as model system and extending this work to Puccinia graminis f. sp. tritici (Pgt) (wheat stem rust) which is one of the most destructive pathogens of wheat. We recently generated a chromosome level genome assembly for Pgt based on Pacbio sequence and HiC scaffolding, which has enabled us to characterise a number of spontaneous virulence mutants. Most result from complex structural rearrangements in the genome, including translocation events between chromosomes and even exchange of chromosomes between the haploid nuclei of this dikaryotic fungus. This has led to identification of several Avr genes from Pgt, as well as development of new tools for testing effector function in wheat including viral overexpression and wheat protoplast transient expression assays. Avr genes in both M. lini and Pgt encode secreted proteins that are co-ordinately expressed during infection and have roles in suppressing host defense responses. Using transgenic flax rust we have visualised delivery of AvrM:YFP fusion proteins from haustoria to infected host cells