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

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

doi:10.3389/fpls.2019.01776

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

Front Plant Sci. 2020 Feb 4:10:1776. doi: 10.3389/fpls.2019.01776. eCollection 2019.

Authors

Yunna Zhu^{1

2}, Xinmin Huang¹, Yanwei Hao¹, Wei Su¹, Houcheng Liu¹, Guangwen Sun¹, Riyuan Chen¹, Shiwei Song¹

Affiliations

¹ College of Horticulture, South China Agricultural University, Guangzhou, China.
² College of Yingdong Agricultural Science and Engineering, Shaoguan University, Shaoguan, China.

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.

Keywords: AMT1.2; Brassica campestris; NH4+ flux; NO3– flux; interaction.