The NPR1 homolog GhNPR1 plays an important role in the defense response of Gladiolus hybridus.

KEY MESSAGE: GhNPR1 shares similar functions as Arabidopsis NPR1 . Silencing of GhNPR1 in Gladiolus results in an enhanced susceptibility to Curvularia gladioli. We propose that GhNPR1 plays important roles in plant immunity. Gladiolus plants and corms are susceptible to various types of pathogens including fungi, bacteria and viruses. Understanding the innate defense mechanism in Gladiolus is a prerequisite for the development of new protection strategies. The non-expressor of pathogenesis-related gene 1 (NPR1) and bzip transcription factor TGA2 play a key role in regulating salicylic acid (SA)-mediated systemic acquired resistance (SAR). In this study, the homologous genes, GhNPR1 and GhTGA2, were isolated from Gladiolus and functionally characterized. Expression of GhNPR1 exhibited a 3.8-fold increase in Gladiolus leaves following salicylic acid treatment. A 1332 bp fragment of the GhNPR1 promoter from Gladiolus hybridus was identified. Inducibility of the GhNPR1 promoter by SA was demonstrated using transient expression assays in the leaves of Nicotiana benthamiana. The GhNPR1 protein is located in the nucleus and cytomembrane. GhNPR1 interacts with GhTGA2, as observed using the bimolecular fluorescence complementation system. Overexpression of GhNPR1 in an Arabidopsis npr1 mutant can restore its basal resistance to Pseudomonas syringae pv. tomato DC3000. Silencing of GhNPR1, using a tobacco rattle virus-based silencing vector, resulted in an enhanced susceptibility to Curvularia gladioli. In conclusion, these results suggest that GhNPR1 plays a pivotal role in the SA-dependent systemic acquired resistance in Gladiolus.