Overexpression of Arabidopsis AtmiR408 Gene in Tobacco

MicroRNA miR408 is predicted to target the transcripts for the copper proteins plantacyanin and laccase in Arabidopsis. In this study it was found that miR408 is present in tobacco also. Its accumulation was positively induced by copper deficiency, providing additional evidence for the important role of miR408 in plant responses to nutriment conditions. To examine the functions of miR408 in tobacco, transgenic tobacco lines containing the Arabidopsis AtmiR408 gene were created. Two transgenic lines with miR408 oversupply were chosen for functional characterization. The results showed that miR408 oversupply down-regulated the activities of antioxidant enzymes such as SOD, POD and CAT. As a result, transgenic lines exhibited altered chlorophyll content and seedling root growth, especially under high copper conditions. This suggests that miR408 accumulates in response to copper deficiency and influences plant growth by regulating antioxidant enzymes. It may be that miR408 exists and functions in tobacco in a conserved way similarly to miR408 in Arabidopsis.