Identification and characterization of a PutAMT1;1 gene from Puccinellia tenuiflora.

Yuanyuan Bu,Aimin Zhou,Xinxin Zhang,Bo Sun,Shenkui Liu,Imshik Lee,Els Jm Van Damme

doi:10.1371/journal.pone.0083111

Abstract

Nitrogen is one of the most important limiting factors for plant growth. However, as ammonium is readily converted into ammonia (NH3) when soil pH rises above 8.0, this activity depletes the availability of ammonium (NH4 +) in alkaline soils, consequently preventing the growth of most plant species. The perennial wild grass Puccinellia tenuiflora is one of a few plants able to grow in soils with extremely high salt and alkaline pH (>9.0) levels. Here, we assessed how this species responds to ammonium under such conditions by isolating and analyzing the functions of a putative ammonium transporter (PutAMT1;1). PutAMT1;1 is the first member of the AMT1 (ammonium transporter) family that has been identified in P. tenuiflora. This gene (1) functionally complemented a yeast mutant deficient in ammonium uptake (2), is preferentially expressed in the anther of P. tenuiflora, and (3) is significantly upregulated by ammonium ions in both the shoot and roots. The PutAMT1;1 protein is localized in the plasma membrane and around the nuclear periphery in yeast cells and P. tenuiflora suspension cells. Immunoelectron microscopy analysis also indicated that PutAMT1;1 is localized in the endomembrane. The overexpression of PutAMT1;1 in A. thaliana enhanced plant growth, and increased plant susceptibility to toxic methylammonium (MeA). Here, we confirmed that PutAMT1;1 is an ammonium-inducible ammonium transporter in P. tenuiflora. On the basis of the results of PutAMT1;1 overexpression in A. thaliana, this gene might be useful for improving the root to shoot mobilization of MeA (or NH4 +).

Highlights

Nitrogen is one of the essential macronutrients required for the synthesis of many cellular components, including amino acids, proteins, chlorophyll, nucleic acids, lipids, and a variety of other metabolites containing nitrogen in their structure [1]
Ammonium uptake in plants is mediated by either nonselective ion channels, such as potassium channels or members of the aquaporin family [8,9,10,11], or specific channels belonging to the ammonium transporter (AMT) family [12,13,14]
Several AMT genes have been isolated in plants that differ in their tissue specificity and in their inducibility by nitrogen availability

Summary

Introduction

Nitrogen is one of the essential macronutrients required for the synthesis of many cellular components, including amino acids, proteins, chlorophyll, nucleic acids, lipids, and a variety of other metabolites containing nitrogen in their structure [1]. Subsequent phylogenetic studies indicated that the plant transporters of the AMT family are subdivided into 2 subfamilie: AMT1 and AMT2 [15]. AMT1 subfamily members are expressed in the plant roots [19], and are generally repressed by high nitrogen levels [20]. AMT1 family genes have been shown to regulate root ammonium fluxes in response to cellular and/or whole-plant demand for nitrogen [4,21,22]. All of the membranes of plant AMT proteins studied to date have been found to be localized to the plasma membrane [13,14,17,25,26]

Methods

Results

Conclusion