Functional assessment of the pathogenesis-related protein PR-1b in barley

The pathogenesis-related protein 1 (PR-1b) of barley (Hordeum vulgare L.) is a marker for the attack by the powdery mildew fungus (Blumeria graminis f.sp. hordei, Bgh) and other pathogens. PR-1b consists of 164 amino acids and has a potential signal peptide for export into the cell wall. Here, we show that PR-1b is differentially expressed in near-isogenic barley lines exhibiting various forms of defence phenotypes including papilla formation and the hypersensitive cell death. To elucidate PR-1b function, we transiently silenced PR-1 expression by double stranded RNA (dsRNA) interference in the moderately susceptible barley double mutant line A89 (genotype: mlo5-ror1), which shows a papillae-based defence phenotype. Upon bombardment of leaf segments with PR-1b dsRNA and a GFP marker gene construct, Bgh slightly more frequently penetrated the plant cell wall of transformed epidermal cells relative to cells bombarded with human control dsRNA. We conclude that PR-1b contributes to penetration resistance to the powdery mildew fungus in barley. We also observed that PR-1b expression correlates with the production of H₂C₂ in responses to Bgh and Bipolaris sorokiniana and was induced upon infiltration of the H₂O₂ producing mixture of glucose and glucose oxidase.