TaGSr contributes to low-nitrogen tolerance by optimizing nitrogen uptake and assimilation in Arabidopsis

Glutamine synthetase (GS) is a key enzyme that assimilates ammonium to form glutamine. However, little is known about the function of TaGSr (Triticum aestivum L. root glutamine synthetase) in nitrogen metabolism in wheat. In this study, we evaluated the effects of ectopic expression of TaGSr from wheat on nitrogen uptake, assimilation, and accumulation in Arabidopsis under low nitrogen (LN) conditions. TaGSr was mainly expressed in vascular tissues and dramatically induced by nitrogen deficiency treatment. The transcripts of the TaGSr-4A and TaGSr-4D were relatively more abundant compared with TaGSr-4B. We observed that the growth performance of ectopic expression of TaGSr from wheat in Arabidopsis transgenic plants were better than that of Col-0. The dry weight, NO3--N, NH4+-N, free amino acid content, the total N accumulation of shoot in TaGSr Arabidopsis were significantly higher than that of Col-0 under both low and high nitrogen conditions. In conclusion, TaGSr positively promotes the growth and biomass of Arabidopsis via up-regulating expression of genes involved in N uptake, transport and assimilation, significantly contributing to the tolerance to LN stress.