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Overexpression of a pH-sensitive nitrate transporter in rice increases crop yields

Significance Significant progress has been made in our understanding of plant adaptive responses to maintain cellular pH under varied N supply forms. Rice is a plant adapted to grow in waterlogged or dryland environments, in contrast to other crops, such as wheat, soybean, and maize. The nitrate transporter OsNRT2.3b provides a molecular mechanism explaining plant adaptation to the ammonium-nitrate supply shift between the waterlogged and drained soil environments. The sensing of cytosolic pH by OsNRT2.3b can function to improve rice nitrogen use efficiency and pH balance, providing an explanation for plant adaptation to changes in the form of N supply. Cellular pH homeostasis is fundamental for life, and all cells adapt to maintain this balance. In plants, the chemical form of nitrogen supply, nitrate and ammonium, is one of the cellular pH dominators. We report that the rice nitrate transporter OsNRT2.3 is transcribed into two spliced isoforms with a natural variation in expression ratio. One splice form, OsNRT2.3b is located on the plasma membrane, is expressed mainly in the phloem, and has a regulatory motif on the cytosolic side that acts to switch nitrate transport activity on or off by a pH-sensing mechanism. High OsNRT2.3b expression in rice enhances the pH-buffering capacity of the plant, increasing N, Fe, and P uptake. In field trials, increased expression of OsNRT2.3b improved grain yield and nitrogen use efficiency (NUE) by 40%. These results indicate that pH sensing by the rice nitrate transporter OsNRT2.3b is important for plant adaption to varied N supply forms and can provide a target for improving NUE.