Overexpression of rice phosphate transporter gene OsPT2 enhances nitrogen fixation and ammonium assimilation in transgenic soybean under phosphorus deficiency

Phosphorus (P) deficiency is one of the major factors that limit legume nodulation and nitrogen (N) fixation, and thus legume productivity. In our previous study, we showed that three T-2 transgenic soybean lines overexpressing rice phosphate transporter gene OsPT2 showed enhanced tolerance to low P stress. This study aimed to determine whether OsPT2 overexpression would increase N-2 fixation and ammonium assimilation in three T-3 homozygous transgenic lines (HTLs) under P deficiency in pot culture. Under low inorganic phosphate (Pi) conditions, the P accumulation, total N and total ureide concentrations were significantly higher in the T-3 HTLs than in the wild type (WT) plants. Further, the T-3 HTLs showed significantly better plant growth performance and nodule development than the WT plants under low-Pi conditions. Quantitative real-time PCR (qRT-PCR) analysis showed that the expression levels of GmENOD40-1, GmENOD40-2 (two early nodulin genes), and GmLba (one leghemoglobin gene) were significantly increased in T-3 HTLs under P deficiency at 24 and 32 d after inoculation (DAI). The increased transcript levels of GmGS1 beta 1 and GmGS1 beta 2 (two cytosolic glutamine synthetase genes) in the T-3 HTLs were consistent with the increase in glutamine synthetase (GS, EC 6.3.1.2) activity at 32 DAI. Our results indicated that the overexpression of OsPT2 in T-3 HTLs enhances N-2 fixation and ammonium assimilation activity under low P stress.