Analysis Of Molecular Characteristics And Functional Evaluation Of Efficiency Of A Glutamine Synthetaseâ…  Transgenic Event For Low-nitrogen Tolerance In Maize

Glutamine synthetase catalyze the synthesis of glutamine, which is involved in plant nitrogen-containing compounds metabolism. Glutamine synthetase in plants is divided into two categories, which are cytosolic glutamine synthetaseâ… (GS1) and plastidotypic glutamine synthetaseâ…¡(GS2). GS1 locates mainly in non-photosynthetic organs, and guides synthesis of glutamine with glutamate synthase(GOGAT). It plays an important role in assimilation and re-assimilation of NH4+. Therefore, the research and application of GS1 is important for crop nitrogen use efficiency.This study used T2 generation of maize glutamine synthetase â…  gene overexpression transgenic events(zmGS1ox). Positive zmGS1 ox plants in T2 generation were treated with different nitrogen level with negetive plants as control. copy number, gene expression, and phenotypic evaluation were carried out. The results were as follows:1.Overexpression of GS1 improved maize adaptation under LN stress condition. Overexpression of glutamine synthetase gene reduced the accumulation of anthocyanin in plant stem, root-shoot ratio, root length and root surface area under LN treatment.2.Overexpression of GS1 increased the GS1 transcriptional level in main organs of maize. The transcriptional level of GS1 in root and leaves, chlorophyll content, and GS1 enzyme activity in root were all significantly higher than of the control under LN condition. Overexpression of exogenous gene gave rise to increase of chlorophyll content and the activity of GS1. It is suggest that due to the suppression at the translational regulation of GS in leaves at seeding stage, activity of GS1 did not increase significantly in LN and NN conditions.3.Overexpression of GS1 can increase the content of chlorophyll in leaves and photosynthesis, improve the photochemical efficiency of the blade. The SPAD of overexpression lines were significantly higher than that of the control in LN. The SPAD of overexpression lines at seeding and flowering stage were significantly higher than that of the control in NN. There was no significant difference between the two lines in NN after pollination. The SPAD of overexpression line is higher than that of the control in LN and NN. There are some photosynthetic physiological differences between the overexpression line and the control. Yield(max) and Yield(light) of overexpression line were significantly higher than that of the control. The Non-photochemical quenching(NPQ) of the control was significantly higher than that of the overexpression line. The actual photochemical efficiency and the efficiency of electron transfer had little difference in NN. The photochemical efficiency of the blade of overexpression line was improved by reducing the non-photochemical quenching.4. Overexpression of GS1 has the potential to improve maize yield. Plant dry weight of overexpression line was significantly higher than that of the control in LN and NN, while grain number and hundred grain weight of overexpression line were higher than that of the control without significant difference. Grain nitrogen content of overexpression line was significantly higher than that of the control in LN. These results showed that the overexpression of GS1 gene has the potential to improve maize yield.