Transient expression of glyoxal oxidase from the Chinese wild grape Vitis pseudoreticulata can suppress powdery mildew in a susceptible genotype

Vitis pseudoreticulata glyoxal oxidase (VpGLOX) was previously isolated from the Chinese wild vine V. pseudoreticulata accession Baihe-35-1 during a screen for genes that are upregulated in response to infection with grapevine powdery mildew (Erysiphe necator, PM). In the present study, a possible function of VpGLOX for defense against PM was investigated using Agrobacterium-mediated transient expression. After optimizing agro-infiltration, VpGLOX was transiently overexpressed in leaves of either PM-susceptible (accession 6-12-2) or PM-resistant (accession 6-12-6) plants. The efficiency of transfection was verified using a beta-glucuronidase (GUS) reporter and was found to comprise most leaf areas regardless of the initial leaf position. Upon infection with E. necator, clear differences were observed with respect to hyphal development between agro-infiltrated leaves and control groups of both, the susceptible and the resistant, genotypes. The expression of VpGLOX was followed by real-time polymerase chain reaction in both genotypes. Whereas in the susceptible host (6-12-2) expression was found to increase only in transfected leaves and remained transient, in the resistant host (6-12-6), a second peak appeared later in transfected leaves, probably representing the response of the endogenous VpGLOX. The data support the interpretation that VpGLOX is sufficient to confer resistance to E. necator.