Erysiphe cichoracearum UCSD is a virulent fungal isolate that causes disease on Arabidopsis thaliana Col-0 plants. A key early step for establishment of plant disease is the development of fungal haustorium. We here characterize the transcriptome of susceptible plants at this stage of infection and evaluate the contributions of salicylic acid (SA) and jasmonic acid (JA) to this interaction. cDNA microarrays (AFGC; 11500 ESTs; 4 biological replicates) were hybridized with labeled cDNAs derived from healthy and infected leaf tissues of Col-0 plants and npr-1 or jar-1 mutants impaired in SA and JA signaling, respectively. Stringent statistic analysis (Significance Analysis of Microarrays and ANOVA) allowed us to identify 173 genes affected with similar pattern by infection in all three plants. These genes might be putative markers of plant susceptibility. On the other hand, differential gene expression among wild type and mutant plants was studied. For that purpose, a standardized differences matrix was performed to further develop Principal Component Analysis (PCA). The second and third principal components define a bidimentional space were genes were clustered in four groups by Cluster Analysis. Genes sensitive to SA and JA were therefore identified. Expression profiles of a discrete number of genes selected by both kind of analysis (susceptibility, JA- SA dependence) were confirmed by Northern blots.
