Highly effective expression of glutamine synthetase genes GS1 and GS2 in transgenic rice plants increases nitrogen-deficiency tolerance.

Glutamine synthetase (GS, EC6.3.1.2) is a key enzyme in ammonia assimilation both in plants and in Gram-negative microorganisms. It plays an important role in efficient use of nitrogen sources and nitrogen metabolism in organisms. Two groups of GS isoenzymes, plastidic (GS2) and cytosolic (GS1), have been identified in higher plants. A plant constitutive expression vector p2GS harboring GS1 and GS2 under the control of rice actin 1 (Act1) and maize ubiquitin (Ubi) promoters was constructed for the first time in a single plasmid, and 3 rounds of ligation and transformation were performed. There has been no report about studies on rice transformation with the two GS enzymes (GS1 and GS2). The p2GS thus constructed was introduced into rice var. Zhonghua 10 by Agrobacterium-mediated transfer method, and transgenic plants with resistance to hygromycin (Hyg) were obtained. Results of PCR and Southern blot analysis showed that the foreign genes have been integrated into the rice genome. The transcription of GS1-GS2 genes in the transformants was also confirmed by Northern blot analysis. The transgenic rice plants thus obtained can grow well in an MS medium in which the nitrogen source was replaced by (NH(4))(2)SO(4) 0.7 mmol/L, and fresh weight of the transformants was significantly higher than the control rice plants. The result suggests that expression of p2GS makes the transgenic rice plants tolerant to nitrogen-deficiency.