Overexpression of a High-Affinity Nitrate Transporter OsNRT2.1 Increases Yield and Manganese Accumulation in Rice Under Alternating Wet and Dry Condition.

Bingbing Luo,Guohua Xu,Bin Li,Hong Lu,Longlong Zhu,Shuhua Liu,Guoyou Ye,Xiaorong Fan,Jingguang Chen

doi:10.3389/fpls.2018.01192

Abstract

Nitrate and manganese (Mn) are necessary elements for the growth and development of rice in paddy soil. Under physiological conditions, we previously reported that the uptake of Mn in roots can be improved by the addition of external nitrate but not ammonium. To investigate the mechanism(s) of this phenotype, we produced plant lines overexpressing OsNRT2.1 and assessed Mn uptake under alternating wet and dry (AWD) and waterlogged (WL) conditions. Under AWD condition, we observed a 31% reduction in grain yields of wild type (WT) plants compared to WL condition. Interestingly, the overexpression of OsNRT2.1 could recover this loss, as OsNRT2.1 transgenic lines displayed higher grain yields than WT plants. We also observed 60% higher grain Mn in the transgenic lines in AWD condition and approximately 30% higher Mn in the grain of transgenic lines in WL condition. We further found that the overexpression of OsNRT2.1 did not alter Mg and Fe in the seeds in either growth condition. The reasons for the increased Mn content in OsNRT2.1 transgenic seeds in AWD condition could be explained by the elevated expression of OsNRAMP family genes including OsNRAMP3, OsNRAMP5, and OsNRAMP6 in node I, the panicle-neck, and the flag leaves. The mechanism(s) underpinning the upregulation of these genes requires further investigation. Taken together, our results provide a new function of OsNRT2.1 in improving rice yields and grain Mn accumulation during water-saving cultivation patterns. This represents a new strategy for maintaining yield and improving food quality in a sustainable agricultural system.

Highlights

Trace elements play a vital role in plant growth and development (Yan et al, 2006)
The expression of Mn transporters OsNRAMP3/OsNRAMP5/OsNRAMP6 increased following NO3− treatment compared with NH4+ treatment. These results reveal that both Mn uptake and OsNRAMP3/OsNRAMP5/OsNRAMP6 expression are increased by NO3−
The concentration of Fe and Mg in seeds and husk appeared to vary irregularly (Supplementary Figure S7). This presented the unity of the Mn element. These results demonstrate that rice planted in AWD condition displays higher total N and Mn concentrations in grain, for OsNRT2.1 transgenic lines

Summary

Introduction

Trace elements play a vital role in plant growth and development (Yan et al, 2006). All organisms require trace levels of manganese (Mn) for survival due to its necessity during plant metabolism and its participation in several important pathways (Socha and Guerinot, 2014) including the oxygen-evolving complex (OEX) of photosystem II (PS II). Overexpression of OsNRT2.1 Can Improve Manganese Accumulated role during phosphoenolpyruvate carboxykinase activation and liquid metabolism (Dziwornu et al, 2018). It is required for photosynthesis indirectly by repressing thylakoid synthesis. Mn deficient plants are more vulnerable to cold stress and infections by pathogens, leading to decreased crop yields (Marschner, 1995; Hebbern et al, 2005). Addressing this issue is problematic as Mn2+ rapidly oxidizes when supplemented into fertilizers. The CAX proteins belong to the Ca2+/cation antiporter (CaCA) superfamily (Emery et al, 2012) and are potentially involved in Mn2+/H+ exchange to export Mn from the cytosol (Connorton et al, 2012)

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Discussion

Conclusion