Overexpression of TaNAC2D Displays Opposite Responses to Abiotic Stresses between Seedling and Mature Stage of Transgenic Arabidopsis

Abstract

Environmental stresses frequently affect plant growth and development, and many genes have been found to be induced by unfavorable environmental conditions. Here, we reported the biological functions of <i>TaNAC2D</i>, a stress-related <i>NAC</i> (NAM, ATAF, and CUC) gene from wheat. TaNAC2D showed transcriptional activator activity in yeast. TaNAC2D-GFP fusion protein was localized in the nucleus of wheat mesophyll protoplasts. <i>TaNAC2D</i> transcript abundance was significantly induced by NaCl, PEG6000, and abscisic acid (ABA) at seedling stage, and repressed by NaCl and PEG6000 at mature plant stage. When <i>TaNAC2D</i> was introduced into <i>Arabidopsis</i>, the 35-day-old soil-grown <i>TaNAC2D</i>-overexpression (<i>TaNAC2D</i>-OX) plants displayed slower stomatal closure, higher water loss rate, and more sensitivity to salt and drought stresses compared with WT plants. In contrast, <i>TaNAC2D</i>-OX seedlings, grown on 1/2 MS medium supplemented with different concentrations of NaCl, Mannitol, and MV, had enhanced tolerances to salt, osmotic and oxidative stresses during seed germination and post-germination periods. The opposite stress-responsive phenotypes of transgenic <i>Arabidopsis</i> were consistent with the expression patterns of <i>TaNAC2D</i> in wheat. Moreover, under high salinity and dehydration conditions, three marker genes, including <i>NCED3</i>, <i>RD29A</i>, and <i>RD29B</i>, were down-regulated in 35-day-old <i>TaNAC2D-</i>OX plants grown in soil and up-regulated in 14-day-old <i>TaNAC2D-</i>OX seedlings grown on 1/2 MS medium. Our results suggest that the change in growth stages and environmental conditions may regulate TaNAC2D's function.