We study the Arabidopsis thaliana responses induced by the attack of the virulent fungal pathogen Erysiphe cichoracearum. Although this pathogen leads to development of plant disease, it is expected that host defenses become induced under this interaction. Using microarray expression profiling, we previously characterized plant genes differentially expressed at the stage of haustorium establishment. We here analyze how the classical modulators of host defenses, salicylic acid (SA) and jasmonic acid (JA), contribute to signal plant responses at this stage. For that purpose the expression profiles of infected wild type, npr-1 (impaired in SA pathway) and jar-1 mutants (insensitive to JA) were compared. A Principal Component Analysis was applied to exclude genes insensitive to SA or JA defining four different groups of genes with different expression patterns in wild type, npr-1 and jar-1 plants. Looking for common regulatory elements in each of these gene groups, we found conserved modules of 6 to 12-mer on their promoter regions. Finally, we analyzed the effect of exogenous SA or JA and their mutually inhibitory capacity in the expression levels of these genes.
