Overexpression of Nitrate Transporter OsNRT2.1 Enhances Nitrate-Dependent Root Elongation.

Naz Naz,Fan Fan,Chen Chen,Li Li,Luo Luo,Guo Guo

doi:10.3390/genes10040290

Abstract

Root morphology is essential for plant survival. NO3− is not only a nutrient, but also a signal substance affecting root growth in plants. However, the mechanism of NO3−-mediated root growth in rice remains unclear. In this study, we investigated the effect of OsNRT2.1 on root elongation and nitrate signaling-mediated auxin transport using OsNRT2.1 overexpression lines. We observed that the overexpression of OsNRT2.1 increased the total root length in rice, including the seminal root length, total adventitious root length, and total lateral root length in seminal roots and adventitious roots under 0.5-mM NO3− conditions, but not under 0.5-mM NH4+ conditions. Compared with wild type (WT), the 15NO3− influx rate of OsNRT2.1 transgenic lines increased by 24.3%, and the expressions of auxin transporter genes (OsPIN1a/b/c and OsPIN2) also increased significantly under 0.5-mM NO3− conditions. There were no significant differences in root length, ß-glucuronidase (GUS) activity, and the expressions of OsPIN1a/b/c and OsPIN2 in the pDR5::GUS transgenic line between 0.5-mM NO3− and 0.5-mM NH4+ treatments together with N-1-naphthylphalamic acid (NPA) treatment. When exogenous NPA was added to 0.5-mM NO3− nutrient solution, there were no significant differences in the total root length and expressions of OsPIN1a/b/c and OsPIN2 between transgenic plants and WT, although the 15NO3− influx rate of OsNRT2.1 transgenic lines increased by 25.2%. These results indicated that OsNRT2.1 is involved in the pathway of nitrate-dependent root elongation by regulating auxin transport to roots; i.e., overexpressing OsNRT2.1 promotes an effect on root growth upon NO3− treatment that requires active polar auxin transport.

Highlights

Nitrogen (N) is an essential macronutrient for plant growth and crop productivity [1]
There were no significant differences in grain length, grain width, and 1000-grain weight between OsNRT2.1 transgenic lines and wild type (WT) (Figure S1A–C)
Further analysis showed that the total root length of transgenic plants increased by 38.6% compared with WT under 0.5-mM NO3 − conditions (Figure 3A), including a 24.0% increase in seminal root length (Figure 3B), a 36.4% increase in total adventitious root length (Figure 3C), a 46.0% increase in total lateral root length in the seminal roots (Figure 3F), and a

Summary

Introduction

Nitrogen (N) is an essential macronutrient for plant growth and crop productivity [1]. Plant roots can absorb various forms of nitrogen, including nitrate (NO3 − ), ammonium (NH4 + ), and organic molecules, which are mainly amino acids [2]. NH4 + is the primary form in the paddy fields, and rice prefers NH4 + to NO3 − [3]. NH4 + is absorbed into plants by ammonium transporters (AMTs) [1,2]. Excessive NH4 + in soil is considered to be toxic to rice [1]. NO3 − is usually the most abundant nitrogen source in aerobic soil; this anionic form is soluble in soil water and easy to migrate in soil [4,5]

Methods

Results

Conclusion