The hijacking of barley wall associated kinases by a fungal pathogen, Bipolaris sorokiniana to cause spot blotch disease

Primary author: Gazala Ameen
Co-author(s): Shyam Solanki; Thomas Drader; Lauren Bittara-Sager
Brian Steffenson; Chrysafis Vogiatzis; Robert Brueggeman
Faculty sponsor: Robert S. Brueggeman

Primary college/unit: Agricultural, Human and Natural Resource Sciences
Campus: Pullman

Plants have cell membrane bound immunity receptors that sense the pathogen attack and triggers the signalling to initiate defense responses which mostly result in localized programmed cell death (PCD). This PCD mediated resistance subdues biotrophic pathogens, which survive on living cells but can be hijacked by necrotrophic pathogens, that acquire nutrients from and colonize the resulting dead host cells to further plant diseases. We report that a necrotrophic pathogen Bipolaris sorokiniana, hijacks two barley wall associated kinase (WAK) cell-membrane bound receptors, Sbs1&2, underlying the previously reported rcs5 disease resistance locus on barley chromosome 7H to intentionally trigger the plant immune responses to cause PCD and ultimately causes spot blotch disease. Post-transcriptional gene silencing of Sbs1&2 genes in the susceptible barley lines Steptoe and Harrington resulted in spot blotch resistance, thus, proving that these two WAKs function as susceptibility genes. The expression analysis of Sbs1&2 showed nearly undetectable expression in resistant and susceptible lines prior to pathogen challenge, however, upregulation of both genes specifically occurred in susceptible lines post inoculation. Allele analysis of Sbs1&2 from eight resistant and two susceptible barley lines identified sequence polymorphisms associated with disease phenotypes in the promoter regions indicating that differential transcriptional regulation by virulent isolates contribute to WAK mediated susceptibility. Virulent isolate apoplastic wash fluids induced Sbs1 suggesting regulation by an apoplastic-secreted effector. Thus, the Sbs1&2 genes underlying the rcs5 QTL are the first susceptibility/resistance genes identified that confer resistance against spot blotch, a disease that threatens barley and wheat production worldwide.