Gene Regulation and Global DNA Methylation Changes in White Spruce (Picea glauca) in Response to Copper Contaminations

Plants require metals such as copper to survive, but an excess of metals can have phytotoxic effects. The objectives of this study were to (1) analyze the expression of genes associated with copper resistance (RAN1 and MRP4) and (2) assess the effects of copper and potassium ions on global DNA methylation in white spruce (P. glauca). Seedlings were treated with three concentrations of copper sulfate including 1312 mg/kg, 656 mg/kg, and 130 mg/kg. Potassium sulfate and water were used as controls. DNA and RNA were extracted from roots and needles. The levels of gene expression were measured using RT-qPCR and the global 5-methyl cytosine was assessed using the Abcam ELISA kit procedure. Overall, the highest concentration of copper (1312 mg/kg) induced the most severe damages to plants compared to the 656 mg/kg and 130 mg/kg treatments. Copper at the 1312 mg/kg concentration induced an upregulation of the MRP4 gene in roots and needles. The 656 mg/kg and 130 mg /kg of copper induced no significant difference in MRP4 expression compared to the controls. An upregulation of the RAN1 gene was observed only in roots treated with the 1312 mg/kg. This suggests that the amounts of bioavailable copper in mining sites in Northern Ontario cannot induce changes in MRP4 and RAN1 expressions. Differential expressions of RAN1 and MRP4 genes were observed in roots of copper-resistant and copper-susceptible genotypes. An increase of MRP4 gene expression also observed in the resistant and susceptible genotypes compared to the water control. Copper did not induce changes in the level of global cytosine methylation. However, the potassium ions used as control induced a hypomethylation of DNA at the 1312 mg/kg concentration.

Automated summary

This study analyzed the expression of copper resistance genes (RAN1 and MRP4) and assessed the effects of copper and potassium ions on global DNA methylation in white spruce. The highest concentration of copper induced the most severe damages to plants and upregulated the expression of MRP4 gene in roots and needles. An upregulation of RAN1 gene was observed only in roots treated with the highest copper concentration. Bioavailable copper in mining sites in Northern Ontario did not induce changes in MRP4 and RAN1 expressions. The level of global cytosine methylation was not affected by copper, but the potassium ions used as control induced DNA hypomethylation at the highest copper concentration.