Gene regulation and global DNA methylation mechanisms involved in white spruce (Picea glauca) response to copper toxicity

Abstract

Plants require metals to survive, but an excess of metals can have phytotoxic effects. The objectives of this study were to 1) analyze the transcription of genes associated with copper resistance (RAN1, MT2b, and MRP4) and 2) assess the effects of copper and potassium on global DNA methylation in white spruce (P. glauca). Seedlings were treated with three concentrations of copper sulfate including 1,312 mg/kg, 656 mg/kg, and 130 mg/kg. Potassium sulfate and water 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 sulfate (1,312 mg/kg) induced the most severe damages to plants compared to the 656 mg/kg and 130 mg/kg concentrations. Copper ions at the 1312 mg/kg concentration induced an upregulation of the MRP4 gene in roots and needles. The 656 mg/kg concentration of copper sulfate and potassium sulfate induced an upregulation of MRP4 only in needles. The MT2b gene was upregulated in roots when plants were exposed to 1,312 mg/kg of copper sulfate, but was downregulated in genotypes treated with 656 mg/kg of copper sulfate in both tissues, compared to the water control. The RAN1 gene was upregulated in roots treated with 1,312 mg/kg copper sulfate. Differential expression of RAN1, MT2b, and MRP4 genes were observed in copper-resistant and susceptible genotypes. The present study revealed that potassium ions induced a hypomethylation of DNA at the 1,312 mg/kg concentration while copper did not induce changes in the level of global cytosine methylation.