Assessing differential expression of genes associated with nickel resistance in jack pine (Pinus banksiana) and eastern white pine (Pinus strobus): effects of nickel toxicity

Abstract

Eastern white pine (Pinus strobus) and jack pine (P. banksiana) represent two of the major coniferous species planted in the metal contaminated region of Northern Ontario. Studies on coping mechanisms of these two species to soil metal contamination are limited. The main objectives of the present project were to 1) determine how these two species respond to soil nickel (Ni) contamination and 2) assess the effects of different doses of nickel on the expression of six genes associated with Ni resistance. These genes include high affinity Ni transporter family (AT2G16800), 1-aminocyclopropane-1-carboxylic acid deaminase (ACC deaminase), Natural resistance-associated macrophage proteins (NRAMP3), and serine acetyltransferase (SAT), Nicotianamine synthase (NAS) and Glutathione reductase (GR). Seedlings were grown in soils treated with increasing concentrations of Ni(NO3)2. Potassium nitrate (KNO3) was used to control for potential toxicity of nitrate ions. Gene expression was assessed using RT-qPCR. Damage ratings reveal that P. banksiana is sensitive to Ni(NO3)2 doses of 1,600 and 3,200 mg/kg as well as 3,200 mg/kg KNO3. However, P. strobus was tolerant to all treatment. Soil Ni treatments induced a downregulation of NAS in P. strobus as well as AT2G16800 and NRAMP3 in both species with the severity increasing at high doses of Ni. An upregulation of ACC in both species consistent with an inverted-U hormetic effect was observed. Ni also triggered a hormetic U-effect downregulation of SAT in P. strobus with the lowest dose showing the highest repression. An opposite trend was observed in P. banksiana where Ni induced an upregulation of SAT. Moreover, GR induced an inverted-U hormetic upregulation in P. banksiana. Knowing the coping mechanisms of these conifers to metal contamination is essential for ensuring their longterm sustainability.