Li Wenxin, Feng Zimao, Zhang Chunxia
State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, 26 Xinong Road, Yangling 712100, China.
College of Forestry, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China.
Tree Physiol. 2021 Dec 4;41(12):2392-2408. doi: 10.1093/treephys/tpab071.
Ammonium (NH4+) is a primary nitrogen (N) source for many species, and NH4+ uptake is mediated by various transporters. However, the effects of NH4+ transporters on N uptake and metabolism under salt stress remain unclear. In the present study, we investigated the expression characteristics and transport function of PsAMT1.2 in Populus simonii and its role in ammonium uptake and metabolism under salt stress. PsAMT1.2 was localized in the plasma membrane highly expressed in the roots. Heterologous functionality tests demonstrated that PsAMT1.2 mediates NH4+ permeation across the plasma membrane in yeast mutants, restoring growth. A short-term NH4+ uptake experiment showed that PsAMT1.2 is a high-affinity NH4+ transporter with a Km value of 80.603 μM for NH4+. Compared with the wild type (WT, Populus tremula × Populus alba INRA 717-IB4 genotype), PsAMT1.2-overexpressing transgenic poplar grew better, with higher increases in stem height and relative chlorophyll content under both control and salt-stress conditions. PsAMT1.2 overexpression significantly increased the total NH4+ concentration and total N of whole plants under salt stress. The glutamate synthase (GS), glutamine synthetase (GOGAT) and glutamate dehydrogenase (GDH) activities and the total amino acids largely increased in the roots of PsAMT1.2-overexpressing transgenic plants compared with the WT plants under control conditions, suggesting that PsAMT1.2 overexpression promotes NH4+ assimilation and metabolism in poplar roots. Consistent with the increased total amino acid content, GS1.3, GS2 and Fd-GOGAT expression was upregulated in the roots and leaves of the PsAMT1.2-overexpressing transgenic plants compared with the WT plants under salt stress. Collectively, PsAMT1.2 encodes a high-affinity NH4+ transporter crucial to NH4+ uptake and metabolism under salt stress.
铵（NH4+）是许多物种的主要氮源，NH4+的吸收由多种转运蛋白介导。然而，盐胁迫下NH4+转运蛋白对氮吸收和代谢的影响仍不清楚。在本研究中，我们调查了小叶杨中PsAMT1.2的表达特征和转运功能及其在盐胁迫下对铵吸收和代谢的作用。PsAMT1.2定位于根中高表达的质膜上。异源功能测试表明，PsAMT1.2介导NH4+透过酵母突变体质膜，恢复生长。短期NH4+吸收实验表明，PsAMT1.2是一种高亲和力的NH4+转运蛋白，对NH4+的Km值为80.603 μM。与野生型（WT，欧洲山杨×银白杨INRA 717-IB4基因型）相比，过表达PsAMT1.2的转基因杨树生长更好，在对照和盐胁迫条件下茎高和相对叶绿素含量增加更高。在盐胁迫下，PsAMT1.2过表达显著增加了全株的总NH4+浓度和总氮量。与对照条件下的野生型植株相比，过表达PsAMT1.2的转基因植株根中的谷氨酸合酶（GS）、谷氨酰胺合成酶（GOGAT）和谷氨酸脱氢酶（GDH）活性以及总氨基酸含量大幅增加，表明PsAMT1.2过表达促进了杨树根中NH4+的同化和代谢。与总氨基酸含量增加一致，在盐胁迫下，过表达PsAMT1.2的转基因植株根和叶中GS1.3、GS2和Fd-GOGAT的表达上调。总的来说，PsAMT1.2编码一种高亲和力的NH4+转运蛋白，对盐胁迫下NH4+的吸收和代谢至关重要。
