Drought tolerance evaluation of tobacco plants transformed with different set of genes under laboratory and field conditions

Although extensive studies have demonstrated that many drought-responsive genes confer drought tolerance to plants, comparisons of the drought tolerance capabilities conferred by different genes under various natural conditions have seldom been reported. We evaluated and compared the effects of two sets of transgenes, the drought-responsive genes (AtDREB1B and AtCBL1) and the root architecture-regulated genes (iaaM and AtCKX), on drought tolerance in Nicotiana tabacum plants subjected to different conditions. The expression of AtCKX3 driven by a root-specific promoter PYK10 (designated hereafter as P10; P10:AtCKX3), 35S:AtCKX3, or P10:iaaM promoted root growth and development. Compared to plants harboring P10:AtCKX3, 35S:AtCKX3, P10:iaaM, or the empty vector, those carrying 35S:AtDREB1B, 35S:AtCBL1, or 35S:iaaM exhibited increased drought tolerance under laboratory-controlled conditions. Conversely, in field conditions, plants transformed with 35S:AtDREB1, 35S:AtCBL1, or 35S:iaaM were sensitive to drought stress. Under field conditions, drought stress dramatically reduced the growth and seed production of plants harboring 35S:AtDREB1B, 35S:AtCBL1, 35S:iaaM, or the empty vector, whereas it had little effect on plants carrying P10:AtCKX3, 35S:AtCKX3, or P10:iaaM. This study demonstrates that a plant's tolerance to drought stress changes with environmental conditions, and our results indicates that manipulating the expression of genes that control root architecture may be important for engineering plants with improved drought tolerance in natural conditions.