Hr-Positive Phenotype of the Pseudomonas syringae pv. syringae hrpK Mutant and hrp Gene Superinduction in Tobacco Leaves Treated with Protein Synthesis Inhibitors

Abstract

Induction period-dependent expression of bacterial hrp (hypersensitive response and pathogenicity) genes is required to cause the hypersensitive reaction (HR) in an incompatible piani. Early induced resistance (EIR) is described as a local and fast (in 3-6 h) developing, light-independent reaction of plants thai can prevent HR. Recently it was found that the same bacterial inoculum can trigger both EIR and HR. A short heai-treatment (50°C, 15 sec) or cycioheximide nullifies EIR’s effect. Here we show thai in heat- or cycloheximide-treated incompatible tobacco leaves, hrpK mutant of Pseudomonas syringae pv. syringae 61 is able to induce the HR, having a significantly longer induction period (3-4 h) than the wild-type parent strain (1 h). Moreover, mutant’s growth is potentiated and hrpK gene is superinduced under these EiR-inhibitory conditions. These data suggest that 1) hrpK mutant triggers EIR beside having the capacity for inducing HR; 2) a mutation in brpK gene extends HR induction period; 3) the faster developing EIR relative to this delayed HR-inducing activity may be responsible for the HR(-)-phenotype of hrpK mutant; 4) the HR-preventive effect of EIR may involve inhibition of hrp gene activity of incompatible bacterial pathogens.