Analysis of Gene Expression Associated with Copper Toxicity in White Birch (Betula papyrifera) Populations from a Mining Region

The Greater Sudbury Region (GSR) is one of the most ecologically disturbed regions of Canada. Recent studies have shown that Betula papyrifera accumulate metals in roots or leaves. The main objectives of the present study were to 1) determine the effects of copper treatment on B. papyrifera under controlled conditions and 2) assess the level of expression of genes associated with copper resistance in B. papyrifera populations from metal-contaminated and uncontaminated areas. Significant differences for damage rating were observed among copper dosages after eight days of treatment. There was also a trend of reduced plant growth as the dosage increased. RT- qPCR analysis showed 2x to 25x increase in leaves compared to roots of the expression of the gene for Multi-drug resistance associated protein (MRP4) belonging to the subfamily of ATP-binding cassette (ABC) transporters. A significant upregulation (ranging from 3x to 8 x increase) of the Metallothioneins (MT2B) gene in leaves compared to roots was also observed in three of the five sites studied. There were significant differences in expression of MRP4 and MT2 genes among sites, but no association between metal contamination and gene expression was identified. Likewise, no difference in expression of targeted genes was observed among the copper dosages used in growth chamber experiments.