OsNPF3.1, a nitrate, abscisic acid and gibberellin transporter gene, is essential for rice tillering and nitrogen utilization efficiency

Abstract

Low-affinity nitrate transporter genes have been identified in subfamilies 4–8 of the rice nitrate transporter 1 (NRT1)/peptide transporter family (NPF), but the OsNPF3 subfamily responsible for nitrate and phytohormone transport and rice growth and development remains unknown. In this study, we described OsNPF3.1 as an essential nitrate and phytohormone transporter gene for rice tillering and nitrogen utilization efficiency (NUtE). OsNPF3.1 possesses four major haplotypes of its promoter sequence in 517 cultivars, and its expression is positively associated with tiller number. Its expression was higher in the basal part, culm, and leaf blade than in other parts of the plant, and was strongly induced by nitrate, abscisic acid (ABA) and gibberellin 3 (GA3) in the root and shoot of rice. Electrophysiological experiments demonstrated that OsNPF3.1 is a pH-dependent low-affinity nitrate transporter, with rice protoplast uptake assays showing it to be an ABA and GA3 transporter. OsNPF3.1 overexpression significantly promoted ABA accumulation in the roots and GA accumulation in the basal part of the plant which inhibited axillary bud outgrowth and rice tillering, especially at high nitrate concentrations. The NUtE of OsNPF3.1-overexpressing plants was enhanced under low and medium nitrate concentrations, whereas the NUtE of OsNPF3.1 clustered regularly interspaced short palindromic repeats (CRISPR) plants was increased under high nitrate concentrations. The results indicate that OsNPF3.1 transports nitrate and phytohormones in different rice tissues under different nitrate concentrations. The altered OsNPF3.1 expression improves NUtE in the OsNPF3.1-overexpressing and CRISPR lines at low and high nitrate concentrations, respectively.

Keywords

• rice tillering
• grain yield
• phytohormone
• nitrate
• transporter
• nitrogen utilization efficiency