Transcriptome analysis of O3-exposed Arabidopsis reveals that multiple signal pathways act mutually antagonistically to induce gene expression.

To analyze cellular responses to ozone (O3), we performed a large-scale analysis of the Arabidopsis transcriptome after plants were exposed to O3 for 12 h. By using cDNA macroarray technology, we identified 205 non-redundant expressed sequence tags (ESTs) that were regulated by O3. Of these, 157 were induced and 48 were suppressed by O3. A substantial proportion of these ESTs had predicted functions in cell rescue/defense processes. Using these isolated ESTs, we also undertook a comprehensive investigation of how three hormones, ethylene (ET), jasmonic acid (JA), and salicylic acid (SA), interact to regulate O3-induced genes in various genetic backgrounds of Arabidopsis, such as the ET-insensitive ein2-1, JA-resistant jar1-1, and SA-insensitive npr1-1. The expression of half of the 157 induced genes, especially cell rescue/defense genes, was controlled by ET and JA signaling, indicating that O3-induced defense gene expression at this stage was mainly regulated by ET and JA. Clustering analysis of the 157 O3-induced gene expressions revealed that multiple signal pathways act mutually antagonistically to induce the expression of these genes, and many cell rescue/defense genes induced by ET and JA signal pathways were suppressed by SA signaling, suggesting that the SA pathway acts as a strong antagonist to gene expression induced by ET and JA signaling.