Overexpression of Arabidopsis Dof1, GS1 and GS2 Enhanced Nitrogen Assimilation in Transgenic Tobacco Grown Under Low-Nitrogen Conditions

Nitrogen metabolism is essential for plant growth and development. The glutamine synthetase (GS) enzyme and the Dof transcription factor play important roles in the regulation of nitrogen metabolism. Using expression vectors, transgenic tobacco lines overexpressing each of Dof1 (Dof1.7), GS1 (GLN1;4) and GS2 were developed. cDNA clones of each of these transgenes were derived from Arabidopsis thaliana, and each transgene was under the control of the Rubisco small subunit promoter, PrbcS—a leaf-specific light-inducible promoter. Under low-nitrogen conditions, plant length, leaf surface, total protein, chlorophyll, as well as sucrose and glucose contents in leaves of transgenic tobacco lines were higher than those of wild-type plants. In addition, transgenic plants exhibited increased activities of enzymes involved in carbon and nitrogen metabolism, such as GS, nitrate reductase (NR), phosphoenolpyruvate carboxylase (PEPC) and pyruvate kinase (PK). The contents of most amino acids were significantly higher in transgenic plants than those of wild-type plants, whereas levels of nitrate, malic acid, and citric acid were significantly lower than those of wild-type plants. These findings suggest that Dof1 and GS work together to regulate the nitrogen metabolic pathway in plants, and this enhances nitrogen assimilation in transgenic tobacco plants grown under low-nitrogen conditions.