OsAMT1.1 Expression by Nitrate-Inducible Promoter of OsNAR2.1 Increases Nitrogen Use Efficiency and Rice Yield

Nitrate（NO3-） and ammonium（NH4+） are two main inorganic nitrogen（N） sources during crop growth.Here,we enhanced the expression of OsAMT1.1,which encodes a NH4+ transporter,using the NO3--inducible promoter of OsNAR2.1 and an ubiquitin promoter in transgenic rice plants.Under field condition of 120 kg/hm2 N,agronomic N use efficiency,N recovery efficiency and N transport efficiency,and grain yield of the pOsNAR2.1:OsAMT1.1 transgenic lines were increased compared with those of the wild type（WT） and the pUbi:OsAMT1.1 transgenic plants.Under 2.0 mmol/L NO3-+0.5 mmol/L NH4+ and0.5 mmol/L NO3-+2.0 mmol/L NH4+ conditions of hydroponic culture,compared with the WT,both biomass and total N content were increased in the pOsNAR2.1:OsAMT1.1 transgenic lines.However,biomass was significantly reduced in pUbi:OsAMT1.1 transgenic plants under 0.5 mmol/L NO3-+2.0 mmol/L NH4+condition.The lines expressing pOsNAR2.1:OsAMT1.1 exhibited increased OsAMT1.1 expression and15NH4+ influx in roots under both 2.0 mmol/L NO3-+0.5 mmol/L NH4+ and 0.5 mmol/L NO3-+2.0 mmol/L NH4+conditions.Our study showed that expression of OsAMT1.1 can be promoted when driven by the OsNAR2.1 promoter,especially under high-level nitrate condition,leading to enhancement of NH4+uptake,N use efficiency and grain yield.