Coordinated plant defense responses in Arabidopsis revealed by microarray analysis

Disease resistance is associated with a plant defense response that involve s an integrated set of signal transduction pathways. Changes in the express ion patterns of 2.375 selected genes were examined simultaneously by cDNA m icroarray analysis in Arabidopsis thaliana after inoculation with an incomp atible fungal pathogen Alternaria brassicicola or treatment with the defens e-related signaling molecules salicylic acid (SA), methyl jasmonate (MJ), o r ethylene, Substantial changes (up- and down-regulation) in the steady-sta te abundance of 705 mRNAs were observed in response to one or more of the t reatments, including known and putative defense-related genes and 106 genes with no previously described function or homology, In leaf tissue inoculat ed with A. brassicicola, the abundance of 168 mRNAs was increased more than 2.5-fold, whereas that of 39 mRNAs was reduced. Similarly, the abundance o f 192, 221, and 55 mRNAs was highly (>2.5-fold) increased after treatment w ith SA, MJ, and ethylene, respectively. Data analysis revealed a surprising level of coordinated defense responses, including 169 mRNAs regulated by m ultiple treatments/defense pathways. The largest number of genes coinduced (one of four induced genes) and corepressed was found after treatments with SA and MJ. In addition, 50% of the genes induced by ethylene treatment wer e also induced by MJ treatment. These results indicated the existence of a substantial network of regulatory interactions and coordination occurring d uring plant defense among the different defense signaling pathways, notably between the salicylate and jasmonate pathways that were previously thought to act in an antagonistic fashion.