Overexpressed glutamine synthetase gene modifies nitrogen metabolism and abiotic stress responses in rice

Glutamine synthetase (GS; EC 6.3.1.2) is a key enzyme in nitrogen metabolism; it catalyzes the critical incorporation of inorganic ammonium into glutamine. Two full-length cDNAs that encode the rice (Oryza sativa) cytosolic glutamine synthetase1 genes (OsGS1;1 and OsGS1;2) were isolated from a Minghui 63 normalized cDNA library, and glnA encoding GS in Escherichia coli was isolated by PCR amplification. Transformants for GS gene (GS1;1, GS1;2, and glnA) in rice were produced by an Agrobacterium tumefaciens-mediated transformation method, and transcripts of GS gene accumulated at higher levels in the primary transgenic plants. Our results indicated an increased metabolic level in GS-overexpressed plants, which showed higher total GS activities and soluble protein concentrations in leaves and higher total amino acids and total nitrogen content in the whole plant. Decreases in both grain yield production and total amino acids were observed in seeds of GS-overexpressed plants compared with wild-type plants. In addition, GS1;2-overexpressed plants exhibited resistance to Basta selection and higher sensitivity to salt, drought, and cold stress conditions, whereas the other two types of GS-overexpressed plants failed to show any significant changes for these stress conditions compared with wild-type plants.