Nickel-induced global gene expressions in red maple (Acer rubrum): Effect of nickel concentrations

Red maple (Acer rubrum) does not accumulate nickel in its tissues and has been classified as Ni avoider. The genetic mechanisms involved in this metal avoidance strategy is yet to be defined. Moreover, most of the studies on metal toxicity in plants are conducted in the field where the bioavailable amount of toxic metal is small. Identification of genes whose expression is specifically modified by a toxic metal such as nickel would be useful and should provide a better understanding of their mechanisms of action. The objective of the present study was to assess the effects of different nickel doses on global gene expression in red maple (Acer rubrum). To assess nickel (Ni) toxicity, A. rubrum genotypes were treated with a control (0 mg/kg) and three doses of 150 mg of Ni per 1 kg of soil, 800 mg/kg, and 1600 mg/kg. To determine gene expression, RNA-seq libraries were developed and the De Novo transcriptome was assembled. Comparative analysis revealed significant differential gene expression only when the highest dose (1600 mg/kg) was compared to the lowest dose of Ni (0 mg/kg and 150 mg/kg). In fact, 5753 genes were upregulated and 2382 downregulated when plants treated with 1600 mg of Ni/kg were compared to plants from the 150 mg/kg treatment. These values were 6263 and 3142 when this highest Ni dose was compared to water control, respectively. The threshold for induction of gene response was found to be between 800 mg/kg and 1600 mg/kg of soil nickel. We observed more upregulated than down regulated genes coding for proteins associated with transport and translation in plants exposed to the high Ni dose compared to the low dose and water control. The study suggests that the amount of bioavailable Ni in most highly contaminated mining sites in Canada cannot trigger changes in gene expression in A. rubrum.