Mechanisms of powdery mildew resistance in the Vitaceae family

The cultivated grapevine, Vitis vinifera, is a member of the Vitaceae family, which comprises over 700 species in 14 genera. Vitis vinifera is highly susceptible to the powdery mildew pathogen Erysiphe necator. However, other species within the Vitaceae family have been reported to show resistance to this fungal pathogen, but little is known about the mechanistic basis of this resistance. Therefore, the frequency of successful E. necator penetration events, in addition to programmed cell death (PCD) responses, were investigated in a representative genotype from a range of different species within the Vitaceae family. The results revealed that penetration resistance and PCD-associated responses, or combinations of both, are employed by the different Vitaceae genera to limit E. necator infection. In order to further characterize the cellular processes involved in the observed penetration resistance, specific inhibitors of the actin cytoskeleton and secretory/endocytic vesicle trafficking function were employed. These inhibitors were demonstrated to successfully break the penetration resistance in V. vinifera against the nonadapted powdery mildew E. cichoracearum. However, the use of these inhibitors with the adapted powdery mildew E. necator unexpectedly revealed that, although secretory and endocytic vesicle trafficking pathways play a crucial role in nonhost penetration resistance, the adapted powdery mildew species may actually require these pathways to successfully penetrate the plant host.