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

Treatment with supplementary UV-B resulted in decreases in transcripts of t he photosynthetic genes Lhcb and psbA and concomitant increase in transcrip ts 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 p roduction, UV-B treatment of jar1 and etr1-1 mutants, which are insensitive to JA and ethylene, respectively, showed that the increase in PR-L transcr ipts was dependent on ethylene and PDF1.2 transcripts on both JA and ethyle ne, In contrast, the down-regulation of photosynthetic transcripts was inde pendent of both compounds. Previous studies have indicated a role for react ive oxygen species (ROS) in the W-B-induced down-regulation of the photosyn thetic genes and up-regulation of PR-1 genes. Here we have shown that ROS a re also required for the UV-B-induced up-regulation of PDF1.2 genes. The re sults indicate that the effects of UV-B on the three sets of genes are medi ated 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 mild-type plants, indicated that intact J A and ethylene signal pathways are required for defence against UV-B damage .