Rice fatty acid image-dioxygenase is induced by pathogen attack and heavy metal stress: activation through jasmonate signaling

Plant fatty acid image-dioxygenases (DOXs) catalyze the stereospecific conversion of fatty acids into the corresponding (R)-2-hydroperoxy fatty acids. In several plant species the corresponding gene was shown to be induced by pathogen infection, herbivore attack and environmental stresses. The precise signaling pathway accountable for the induction remains unidentified. In the present study, the effects of bacterial infection, oxidative- and heavy metal-stresses, and plant signaling molecules such as jasmonate, salicylic acid (SA), and ethylene (ET) on expression of a fatty acid image-DOX (OsDOX) gene in rice seedlings were investigated. The rice blight bacteria, Xanthomonas oryzae, elicited the accumulation of OsDOX transcripts in the leaves in both the incompatible and compatible interactions. Treating the seedling with CuSO4 also significantly enhanced the OsDOX expression. The degree of induction was shown to be mostly parallel to the level of endogenous jasmonic acid (JA) in the leaves. In contrast, SA was little effective and ET down-regulated not only the OsDOX expression but also the endogenous level of JA in rice seedlings. These results suggested that the OsDOX gene expression by a variety of stress-related stimuli was activated through jasmonate signaling and was negatively regulated by ET.