COMPARATIVE TRANSCRIPTOMIC RESPONSES TO RHIZOTOXIC STRESSORS, ARSENIC AND JUGLONE EXPOSURE IN RICE

Arsenic (As) is considered as one of the leading toxic metalloid for both animals and plants. In addition, allelochemical juglone is phytotoxic and has been widely studied for allelopathic effects. To help characterize the cellular mechanisms underlying the toxicity of metalloid and allelochemical to plants, the early signalling pathways activated and cellular mechanisms were investigated in rice exposed to As and juglone. Using ROS-sensitive dye and Ca²⁺ indicator, we demonstrated that As and juglone induced ROS production and Ca²⁺ accumulation, respectively. The signalling mechanism of As and juglone stress were analyzed using to gel kinase activity, immunoblot. We found that As and juglone activated, at least, two different mitogen activated protein (MAP) kinases, and CDPKs in rice. Moreover, the NADPH oxidases and CDPK may be involved in As(V)-induced MAP kinase activation.

To gain more insight into cellular responses to As and juglone, we have taken a large-scale analysis of the rice transcriptome during As and juglone stress. Analysis of the DNA microarray data revealed that 1275 and 828 genes were up-regulated in significant response to As and juglone, respectively. We verified the As and jugline-regulated expression of selected signal transduction components, transcription factor, and ROS-associated enzymes by QRT-PCR. The expression of antioxidant genes was also analyzed using enzyme activity assays. These data provide an overview of molecular and cellular changes elicited for further investigation by As and juglone stress in rice roots. Further characterization of the As and juglone-responsive genes identified in this work, may be helpful for a better understanding of the mechanisms of metalloid and allelochemical tolerance in plants.