RT-qPCR Analysis of Host Defense-Related Genes in Nonhost Resistance: Wheat-Bgh Interaction

Non-host resistance (NHR) is a plant defense system against the majority of microbial pathogens. Blumeria graminis f. sp. hordei (Bgh), is an obligate biotrophic ascomycete fungal pathogen that can grow and reproduce only on living cells of wild or domesticated barley (Hordeum sp.). In this study, the expression pattern of eight defense-related genes including NPR1, PR2, PR5, PR1-2, Lipase, LTP, PAL and POX was assessed in bread wheat (Triticum aestivum cv. Darya) against the powdery mildew fungus Bgh. Hydrogen peroxide (H2O2) activity in leaf tissues was also detected histochemically with 3,3-diaminobenzidine (DAB) staining. Result showed that in response to virulence agent, Bgh spores, papillae and hypersensitive response (HR) were formed in the 53.9 and 40.1% of infected area, respectively while in the rest of the infected area (6%) spores were not germinated. According to the histochemical analysis, the wheat NHR against Bgh belongs to type I NHR and display a multi-layered feature including wax composition, pre-formed barriers, papilla formation, hypersensitive response. According to results of expression analysis, the Pox, PR5 and PR1-2 expression level were clearly upregulated 24 hours post inoculation (hpi) and LTP was identified as an early signaling response to Bgh. In this study NPR1 was down regulated during all given time points, thus we suggested that salicylic acid (SA) signaling pathway may be mediated by a NPR1-independent mechanism(s) in wheat-Bgh interaction. The coordinated induction of a set of so-called systemic acquired resistance (SAR) genes including POX, PR1-2 and PR5 was observed in wheat-Bgh interaction. Expression pattern of defense-related genes at the wheat-Bgh interaction can be taken as an indication of their functional relevance at different time points of tissue infection.