Virus-Induced Gene Silencing of a Putative Glutathione S-Transferase Gene Compromised Ol-1-Mediated Resistance against Powdery Mildew in Tomato

Previously, cDNA-amplified fragment length polymorphism analysis was used to profile differentially expressed transcript-derived fragments (DE-TDFs) of tomato between resistant and susceptible responses against the fungal pathogen Oidium neolycopersici. In the present study, we further investigated a DE-TDF annotated to a putative glutathione S-transferase (GST) that was more rapidly upregulated during the Ol-1-mediated resistance response than during the susceptible response. We used virus-induced gene silencing to knock-down expression of the putative GST gene (ShGST) in resistant tomato plants (Solanum habrochiates G1.1560) carrying the Ol-1 gene, and the ShGST-silenced plants showed a susceptible phenotype after inoculation with O. neolycopersici. Microscopic observation demonstrated that O. neolycopersici was able to complete its life cycle on silenced resistant plants and showed similar morphological characteristics to those of the fungus on susceptible tomato plants. The resistance against O. neolycopersici in G1.1560 was associated with hypersensitive response (HR); however, silencing of ShGST did not completely abolish the HR and hydrogen peroxide (H2O2) accumulation. These results indicate that ShGST is required for resistance against O. neolycopersici in tomato and that decreased HR and H2O2 accumulation may be insufficient for tomato to prevent sporulation of O. neolycopersici.