Co-Overexpression ofOsNAR2.1andOsNRT2.3aIncreased Agronomic Nitrogen Use Efficiency in Transgenic Rice Plants

The NO(3)(-)transporter plays an important role in rice nitrogen acquisition and nitrogen-use efficiency. Our previous studies have shown that the high affinity systems for nitrate uptake in rice is mediated by a two-component NRT2/NAR2 transport system. In this study, transgenic plants were successful developed by overexpression ofOsNAR2.1alone,OsNRT2.3aalone and co-overexpression ofOsNAR2.1andOsNRT2.3a. Our field experiments indicated that transgenic lines expressingp35S:OsNAR2.1orp35S:OsNAR2.1-p35S:OsNRT2.3aconstructs exhibited increased grain yields of approximately 14.1% and 24.6% compared with wild-type (cv. Wuyunjing 7, WT) plants, and the agricultural nitrogen use efficiency increased by 15.8% and 28.6%, respectively. Compared with WT, the(15)N influx in roots ofp35S:OsNAR2.1andp35S: OsNAR2.1-p35S:OsNRT2.3alines increased 18.9%-27.8% in response to 0.2 mM, 2.5 mM(15)NO(3)(-), and 1.25 mM(15)NH(4)(15)NO(3), while there was no significant difference betweenp35S:OsNAR2.1andp35S:OsNAR2.1-p35S:OsNRT2.3alines; only the(15)N distribution ratio of shoot to root forp35S:OsNAR2.1-p35S:OsNRT2.3alines increased significantly. However, there were no significant differences in nitrogen use efficiency,N-15 influx in roots and the yield between thep35S:NRT2.3atransgenic lines and WT. This study indicated that co-overexpression ofOsNAR2.1andOsNRT2.3acould increase rice yield and nitrogen use efficiency.