Time course analysis of gene regulation under cadmium stress in rice

To elucidate the regulation of gene expression in response to cadmium (Cd) stress in rice (Oryza sativa), transcriptional changes in roots and shoots were investigated using a 22 K microarray covering 21,495 genes. Rice plants were exposed to 10 μM CdCl2 for 3 h or 1 μM CdCl2 for 24, 48, and 72 h, and 8 days in hydroponic culture. In roots, 1,207 genes were up-regulated, whereas 519 genes were down-regulated by more than twofold under 10 μM Cd stress for 3 h. Compared with roots, the shoots had fewer Cd-responsive genes. The expression of genes such as those encoding cytochrome P450 family proteins, heat shock proteins, and glutathione S-transferase was strongly induced. Genes encoding proteins involved in signal transduction, including transcription factors such as DREB and NAC, and protein kinases, were also induced. Genes involved in photosynthesis were mainly down-regulated after 3 h of stress. Genes for the synthesis of nicotianamine and 2′-deoxymugineic acid were induced in roots under 1 μM Cd stress for 8 days, suggesting the occurrence of iron deficiency under longer-term Cd stress. Cd-regulated transporter genes included PDR and MATE family transporters, which were strongly up-regulated in roots, especially under 10 μM Cd stress, suggesting their role in Cd detoxification via export of Cd from the cytoplasm. Their modification may potentially lead to the development of low-Cd rice, which contributes to human health as well as high-Cd rice useful for phytoremediation.