Elucidating the Molecular Mechanisms of Intermediate Host Resistance in Barley to Wheat Stripe Rust

A plant may be considered a nonhost of a pathogen if all known genotypes of the species are resistant to all known isolates of a pathogen species. However, if a small number of genotypes are susceptible to some known isolates of a pathogen species this plant maybe considered an intermediate host. Barley (Hordeum vulgare L.) is an intermediate host for wheat stripe rust (Puccinia striiformis f. sp. tritici) (PST). Despite significant disease pressure in the field, barley resistance to PST has endured for several decades. We wanted to understand more about the genetic architecture underlying this resistance. Leveraging a combination of linkage mapping, association genetics, and random forest analysis we were able to map a single dominant trait to chromosome 7HL. The gene underlying this trait was provisionally designated as Rpst2 (Resistance to Puccinia striiformis f. sp. tritici2). Next, we integrated RNAseq assemblies and existing anchored whole genome shotgun data to identify candidate genes at the Rpst2 locus using a comparative allele mining approach. A single gene gave a presence/absence expression profile between accessions known to harbour Rpst2 and rpst2 respectively. We are currently investigating the function and potential taxonomic functionality of this gene with transformation in susceptible accessions of barley, wheat, and Brachypodium.