Overexpression of the Transcription Factor NtNAC2 Confers Drought Tolerance in Tobacco

NAC proteins constitute one of the largest families of plant-specific transcription factors and play an important role in biological processes, including plant development and phytohormone homeostasis, and in responses to various environmental stresses. In this study, we isolated an NAC group A gene (named NtNAC2) from Nicotiana tabacum L. Quantitative RT-PCR (qRT-PCR) analysis indicated that NtNAC2 was significantly upregulated under drought stress, which implied NtNAC2 was important in tobacco under such conditions. Overexpression of NtNAC2 in tobacco plants exhibited enhanced drought tolerance by means of improved seedling growth. Under drought stress, organic osmoprotectants were significantly accumulated in these plants. Additionally, the activities of antioxidant defense enzymes, like superoxide dismutase (SOD) and peroxidase (POD), which could effectively scavenge accumulated reactive oxygen species (ROS), increased in NtNAC2-overexpression transgenic tobacco plants compared with wild-type plants. The net photosynthetic rate was also significantly increased in NtNAC2-overexpression transgenic lines compared with wild-type plants, and the content of malondialdehyde (MDA) and proline was lower in NtNAC2-overexpression transgenic lines than that in wild-type plants (P<0.01). Furthermore, the expression of NtWRKY28, a drought resistance gene, was significantly increased and the delta-OAT gene was downregulated in NtNAC2-overexpression plants relative to wild-type plants. Taken together, these results indicated that NtNAC2 functions as a positive regulator of drought stress tolerance. This study provides a basis for further study of drought resistance conferred by the NtNAC2 gene.