Expression of Metallothionein-Like Protein 2B Gene Induced by Different Concentrations of Copper in White Spruce (Picea glauca)

The alterations to the expressions of metal transporter genes can induce metal ion uptake to maintain cell homeostasis when metal concentrations are low. Metallothioneins (MTs) are a class of low molecular mass (4-8 kDa), cysteine (Cys)-rich proteins that can bind metals via the thiol groups of their Cys residues. Studies on MT gene expressions in higher plants, such as conifers, are limited. White spruce (Picea glauca) is a North American native conifer species that are ecologically and economically important. The objective of the study is to determine the effects of different concentrations of copper on MT2b expression in white spruce (P. glauca). Seedlings were treated with three concentrations of copper sulfate including 1,312, 656, and 130 mg/kg. Potassium sulfate and water were used as controls. Total RNA was extracted from roots and needles. The levels of MT2b gene expression were measured using RT-qPCR. The present study reports for the first time, novel information on the effect of copper ions on the expression of MT2b in P. glauca. The MT2b gene was upregulated in roots when seedlings were exposed to 1,312 mg/kg of copper sulfate but were downregulated in genotypes treated with 656 mg/kg of copper sulfate in both tissues when compared to the water control. The expression of the MT2b gene was significantly downregulated in needles of genotypes treated with 656 mg/kg of copper sulfate when compared to the 1,312 mg/kg concentration. The expression of MT2b was higher in roots compared to needles regardless of the concentrations of copper sulfate or potassium sulfate used. MT2b was highly expressed in the roots of copper-resistant genotypes but was inhibited in the roots of susceptible seedlings when compared to the water control.