Ultraviolet‐B‐induced stress and changes in gene expression in Arabidopsis thaliana: role of signalling pathways controlled by jasmonic acid, ethylene and reactive oxygen species

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Abstract
Treatment with supplementary UV‐B resulted in decreases in transcripts of the photosynthetic genes Lhcb and psbA and concomitant increase in transcripts of two pathogen‐related genes, PR‐1 and PDF1·2, in Arabidopsis thaliana. UV‐B exposure caused increases in jasmonic acid (JA) levels and ethylene production. UV‐B treatment of jar1 and etr1‐1 mutants, which are insensitive to JA and ethylene, respectively, showed that the increase in PR‐1 transcripts was dependent on ethylene and PDF1·2 transcripts on both JA and ethylene. In contrast, the down‐regulation of photosynthetic transcripts was independent of both compounds. Previous studies have indicated a role for reactive oxygen species (ROS) in the UV‐B‐induced down‐regulation of the photosynthetic genes and up‐regulation of PR‐1 genes. Here we have shown that ROS are also required for the UV‐B‐induced up‐regulation of PDF1·2 genes. The results indicate that the effects of UV‐B on the three sets of genes are mediated through three distinct signal transduction pathways which are similar, but not identical, to pathways initiated in response to pathogen infection. In addition, the increased sensitivity of both jar1 and etr1‐1 mutants to UV‐B radiation, as compared with wild‐type plants, indicated that intact JA and ethylene signal pathways are required for defence against UV‐B damage.