Ammonium Transporter (BcAMT1.2) Mediates the Interaction of Ammonium and Nitrate in Brassica campestris.

Yunna Zhu,Shiwei Song,Guangwen Sun,Riyuan Chen,Houcheng Liu,Xinmin Huang,Yanwei Hao,Wei Su

doi:10.3389/fpls.2019.01776

Yunna Zhu, Shiwei Song + Show 6 more

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https://doi.org/10.3389/fpls.2019.01776

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Abstract

The provision of ammonium (NH4 +) and nitrate (NO3 −) mixture increases the total nitrogen (N) than the supply of sole NH4 + or NO3 – with the same concentration of total N; thus, the mixture contributes to better growth in Brassica campestris. However, the underlying mechanisms remain unknown. In this study, we analyzed NH4 + and NO3 – fluxes using a scanning ion-selective electrode technique to detect under different N forms and levels in B. campestris roots. We observed that the total N influxes with NH4 + and NO3 − mixture were 1.25- and 3.53-fold higher than those with either sole NH4 + or NO3 −. Furthermore, NH4 + and NO3 – might interact with each other under coexistence. NO3 – had a positive effect on net NH4 + influx, whereas NH4 + had a negative influence on net NO3 – influx. The ammonium transporter (AMT) played a key role in NH4 + absorption and transport. Based on expression analysis, BcAMT1.2 differed from other BcAMT1s in being upregulated by NH4 + or NO3 −. According to sequence analysis and functional complementation in yeast mutant 31019b, AMT1.2 from B. campestris may be a functional AMT. According to the expression pattern of BcAMT1.2, β-glucuronidase activity, and the cellular location of its promoter, BcAMT1.2 may be responsible for NH4 + transport. Following the overexpression of BcAMT1.2 in Arabidopsis, BcAMT1.2-overexpressing lines grew better than wildtype lines at low NH4 + concentration. In the mixture of NH4 + and NO3 –, NH4 + influxes and NO3 – effluxes were induced in BcAMT1.2-overexpressing lines. Furthermore, transcripts of N assimilation genes (AtGLN1.2, AtGLN2, and AtGLT1) were significantly upregulated, in particular, AtGLN1.2 and AtGLT1 were increased by 2.85–8.88 times in roots, and AtGLN1.2 and AtGLN2 were increased by 2.67–4.61 times in leaves. Collectively, these results indicated that BcAMT1.2 may mediate in NH4 + fluxes under the coexistence of NH4 + and NO3 – in B. campestris.

Highlights

The efficiency and availability of nitrogen (N) have decisive influences on plant growth and crop productivity (Hachiya and Sakakibara, 2017)
Compared with fluxes in sole N source, NO3– fluxes were decreased in mixed N forms and NH4+ fluxes were close to the fluxes of sole NH4+ (1 mmol L–1 NH4Cl) which did not decrease with increasing NH4+ concentration (Figures 1A–C)
We subsequently investigated that histochemical staining for BcAMT1.2pro::GUS transformants that were treated with NH4+, NO3, or N-deficiency and stained for GUS activity

Summary

Introduction

The efficiency and availability of nitrogen (N) have decisive influences on plant growth and crop productivity (Hachiya and Sakakibara, 2017). Nitrate (NO3–) and ammonium (NH4+) are major sources of inorganic N. NH4+ at millimolar concentrations in the soil solution or hydroponic culture causes growth suppression and chlorosis (ammonium toxicity) in plants, unlike NO3– at the same concentration (Miller and Cramer, 2004). Extensive studies suggest that a mixture of NO3– and NH4+ nutrition stimulates plant growth beyond that observed with NO3– or NH4+ alone (Britto and Kronzucker, 2001). The use of the mixture enhances N-use efficiency and improves crop productivity (Wang and Shen, 2011; Hachiya et al, 2012)

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