Decrypting the regulation and mechanism of nickel resistance in white birch (Betula papyrifera) using cross-species metal-resistance genes

Abstract

Recent studies have found that many transporters, metabolic products and chelators play a role in heavy metal (HM) resistance in model plants. Knowledge of mechanisms involved in resistance to HM in higher plant species is limited. In the present study, the expression of four novel genes (AT2G16800, GR, ZAT11, and IREG1) in white birch (Betula papyrifera) growing in soil contaminated with different levels of nickel were investigated. B. papyrifera seedlings were treated with different doses of nickel including 5.56, 1600, and 4800 mg/kg in growth chamber screening trials. The expression of targeted genes in nickel resistant and susceptible genotypes was measured using RT-qPCR. Field trials were also conducted to assess the regulation of these genes in B. papyrifera growing in metal-contaminated and uncontaminated sites. The transcription factor ZAT11 was the only gene affected (downregulation) by nickel at the low dose of 5.56 mg/kg. The expression of all the four genes was affected by the high dose of 1600 mg/kg resulting in the downregulation of AT2G16800, GR, and ZAT11 and the upregulation of IREG1. ZAT11 and IREG1 were differentially expressed in resistant genotypes. No differences in gene expression were found when samples from metalcontaminated and reference field sites were compared, but the expression of AT2G16800 and IREG1 was higher in roots compared to leaves. The findings of this study suggest that the bioavailable amounts of nickel that is usually found in highly metal-contaminated soils in mining regions cannot trigger a measurable genetic response in plants.