Comparison of early transcriptome responses to copper and cadmium in rice roots.

The phytotoxic effects of copper (Cu) and cadmium (Cd) on plant growth are well documented. However, Cu and Cd toxicity targets and the cellular systems contributing to acquisition of tolerance are not fully understood at the molecular level. We aimed to identify genes and pathways that discriminate the actions of Cu and Cd in rice roots (Oryza sativa L. cv. TN67). The transcripts of 1,450 and 1,172 genes were regulated after Cu and Cd treatments, respectively. We identified 882 genes specifically respond to Cu treatment, and 604 unique genes as Cd-responsive by comparison of expression profiles of these two regulated gene groups. Gene ontology analysis for 538 genes involved in primary metabolism, oxidation reduction and response to stimulus was changed in response to both metals. In the individual aspect, Cu specifically altered levels of genes involved in vesicle trafficking transport, fatty acid metabolism and cellular component biogenesis. Cd-regulated genes related to unfolded protein binding and sulfate assimilation. To further characterize the functions of vesicle trafficking transport under Cu stress, interference of excytosis in root tissues was conducted by inhibitors and silencing of Exo70 genes. It was demonstrated that vesicle-trafficking is required for mediation of Cu-induced reactive oxygen species (ROS) production in root tissues. These results may provide new insights into understanding the molecular basis of the early metal stress response in plants.