Powdery Mildew- and Salicylic Acid-Induced Gene Expression in Grapevine. Vitis vinifera

Infection by the pathogen grape powdery mildew (Erysiphe necator) causes changes in the transcriptome of its susceptible host Vitis vinifera. Infection triggers the host to synthesize the signaling molecule salicylic acid (SA) which regulates the expression of a broad range of defense-related plant genes. In addition, it is hypothesized that E. necator directly modulates gene expression in V. vinifera via the haustorial complex. This microarray experiment was designed to dissect host transcriptome changes triggered directly by E. necator infection and indirectly through the SA response. We accomplished this by conducting two separate global leaf transcriptome analyses using the Vitis Affymetrix GeneChip platform: in one, we compared the leaves with fully established PM colonies to healthy reference leaves, in another, we compared healthy leaves with artificially elevated SA levels to healthy reference leaves. Overlaying host transcriptome changes from these two experiments enabled us to glean out V. vinifera genes that modulate their expression in response E. necator in an SA-independent manner. Overall design: We characterized gene expression profiles in (1) healthy reference leaves, (2) leaves with well-established by E. necator colonies, and (3) healthy leaves in which SA levels were artificially elevated by the presence of methyl salicylate (15 µM) in the atmosphere. Treatments (1) and (2) differed only in the presence E. necator infection, whereas treatments (1) and (3) differed only in SA levels. Consequently, statistical comparisons were made only between signal intensities from treatments (1) and (2) and from treatments (1) and (3). Each treatment was done in three biological repeats, that is, each experiment was repeated three times in 14-day intervals with dedicated biological material (plants were used in a single replicate and not reused in another repeat or treatment). Each biological replicate consisted of 10 potted vines. For RNA extraction, two young leaves were harvested from each of the 10 vines and pooled into a single sample.