Rice nitrate transporter OsNPF2.4 functions in low-affinity acquisition and long-distance transport

Abstract

Plant proteins belonging to the NPF (formerly NRT1/PTR) family are well represented in every genome and function in transporting a wide variety of substrates. In this study, we showed that rice OsNPF2.4 is located in the plasma membrane and is expressed mainly in the epidermis, xylem parenchyma, and phloem companion cells. Functional analysis in oocytes showed that OsNPF2.4 is a pH-dependent, low-affinity N O 3 - transporter. Short-term 15 N O 3 - influx rate, long-term N O 3 - acquisition by root, and upward transfer from root to shoot were decreased by disruption of OsNPF2.4 and increased by OsNPF2.4 overexpression under high N O 3 - supply. Moreover, the redistribution of N O 3 - in the mutants in comparison with the wild type from the oldest leaf to other organs, particularly to N-starved roots, was dramatically changed. Knockout of OsNPF2.4 decreased rice growth and potassium (K) concentration in xylem sap, root, culm, and sheath, but increased the shoot:root ratio of tissue K under higher N O 3 -. We conclude that OsNPF2.4 functions in acquisition and long-distance transport of N O 3 -, and that altering its expression has an indirect effect on K recycling between the root and shoot.