Redundancy and metabolic function of the glutamine synthetase gene family in poplar.

Vanessa Castro-Rodríguez,Angel García-Gutiérrez,Ma Belén Pascual,Concepción Avila,Francisco M Cánovas,Rafael A Cañas

doi:10.1186/s12870-014-0365-5

Abstract

BackgroundGlutamine synthetase (GS; EC: 6.3.1.2, L-glutamate: ammonia ligase ADP-forming) is a key enzyme in ammonium assimilation and metabolism in higher plants. In poplar, the GS family is organized in 4 groups of duplicated genes, 3 of which code for cytosolic GS isoforms (GS1.1, GS1.2 and GS1.3) and one group that codes for the choroplastic GS isoform (GS2). Our previous work suggested that GS duplicates may have been retained to increase the amount of enzyme in a particular cell type.ResultsThe current study was conducted to test this hypothesis by developing a more comprehensive understanding of the molecular and biochemical characteristics of the poplar GS isoenzymes and by determinating their kinetic parameters. To obtain further insights into the function of the poplar GS genes, in situ hybridization and laser capture microdissections were conducted in different tissues, and the precise GS gene spatial expression patterns were determined in specific cell/tissue types of the leaves, stems and roots. The molecular and functional analysis of the poplar GS family and the precise localization of the corresponding mRNA in different cell types strongly suggest that the GS isoforms play non-redundant roles in poplar tree biology. Furthermore, our results support the proposal that a function of the duplicated genes in specific cell/tissue types is to increase the abundance of the enzymes.ConclusionTaken together, our results reveal that there is no redundancy in the poplar GS family at the whole plant level but it exists in specific cell types where the two duplicated genes are expressed and their gene expression products have similar metabolic roles. Gene redundancy may contribute to the homeostasis of nitrogen metabolism in functions associated with changes in environmental conditions and developmental stages.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0365-5) contains supplementary material, which is available to authorized users.

Highlights

Glutamine synthetase (GS; EC: 6.3.1.2, L-glutamate: ammonia ligase ADP-forming) is a key enzyme in ammonium assimilation and metabolism in higher plants
Total intact RNA was isolated from Populus trichocarpa clone INRA 101–74 and full-length cDNA (FLcDNA) representatives of GS genes were isolated by RT-PCR using specific primers
All poplar GS isoforms were active in bacteria and the specific activities observed varied among the different isoforms, with higher values for cytosolic glutamine synthetase (GS1) isoforms than for chloroplastic glutamine synthetase (GS2) (Figure 1b, upper panel)

Summary

Introduction

Glutamine synthetase (GS; EC: 6.3.1.2, L-glutamate: ammonia ligase ADP-forming) is a key enzyme in ammonium assimilation and metabolism in higher plants. The forest ecosystems play an important role in the production of the world’s biomass. They are a necessary factor that must be considered when addressing climate change and the maintenance of biological diversity. Terrestrial plants have evolved metabolic pathways to assimilate and distribute nitrogen for the biosynthesis of a wide range of molecules. Nitrogen is both essential and limiting, and plants have developed systems to guarantee its economy such as the glutamine synthetase (GS)/glutamate synthase (GOGAT) cycle [3].

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