Characterization of a glutamine synthetase gene BnGS1-2 from ramie (Boehmeria nivea L. Gaud) and biochemical assays of BnGS1-2-over-expressing transgenic tobacco

Glutamine synthetase (GS) plays fundamental roles in nitrogen metabolism in higher plants. Ramie (Boehmeria nivea L. Gaud) has excellent forage and rapid growth characteristics, and isolated BnGS1-2 is closely related to that of legumes, potentially providing gene resources for nitrogen uptake and assimilation. Consequentially, transgenic studies involving the over-expression of BnGS1-2 in Nicotiana tabacum were performed to investigate the potential function and application of BnGS1-2 in higher plants. Comparative analysis of nitrogen use efficiency (NUE) was performed during wild type and independent transgenic lines with various in GS activity at the mRNA and protein levels. Our results indicate that the BnGS1-2-over-expressing transgenic lines significantly enhanced the fresh weight, dry weight and plant height. Simultaneously, the transgenic lines had higher soluble protein content and higher total nitrogen content than the control plants under normal planting condition. The range of enhancement positively associated with BnGS1-2 activities in different transgenic lines. The over-expression of BnGS1-2 in tobacco resulted in a significant decrease in leaf-free NH4 + content. Simultaneously, the transgenic lines increased the NO3 − uptake and NH4 + assimilation with a remarkable increase in the NR activity and no change in the free NO3 − content. These results indicate that BnGS1-2 would be an excellent gene resource for improvement of plants biomass and NUE.