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

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.

Poplar trees for phytoremediation of high levels of nitrate and applications in bioenergy

“…Endogenous GS transcripts in Populus display organ-specific expression profiles (Figure 7) confirming previous studies (Castro-Rodr ıguez et al, 2011). Interestingly, the expression of PtGS1.1 increased more than fourfold in the leaves of WT plants under luxuriant N levels.…”

“…Interestingly, the expression of PtGS1.1 increased more than fourfold in the leaves of WT plants under luxuriant N levels. PtGS1.1 codes for a high-affinity ammonium enzyme that seems to play a crucial role in ammonium recycling in mature leaves (Castro-Rodr ıguez et al, 2015). The ectopically expressed pine GS1a has an expression profile independent of N availability.…”

“…The qPCR was carried out in a thermal cycler CFX384 (Bio-Rad, Hercules, CA) under the following conditions: 3 min at 95°C (1 cycle), 1 s at 95°C and 5 s at 60°C (40 cycles) and a melting curve from 60 to 95°C to verify the reaction specificity. Primers for PtGS1.1, PtGS1.2, PtGS1.3, PtGS2, previously described in Castro-Rodr ıguez et al (2011), and PpGS1a (Forward: 5 0 -AATTACA AAGTGGAGGCCAG; Reverse: 5 0 -AGCCCTCGCCATATTACAA GT) were used. Actin2 and Ubiquitin were used as reference genes (Brunner et al, 2004).…”

“…In poplar, the GS family is organized in four groups of duplicated genes, three of which code for cytosolic GS isoforms (GS1.1, GS1.2 and GS1.3) and one that codes for the plastidic GS isoform (GS2) (Castro‐Rodríguez et al ., ). Recent results support that GS gene redundancy may contribute to the homoeostasis of N metabolism in functions associated with changes in glutamine use in multiple metabolic pathways (Castro‐Rodriguez et al., ).…”

“…A small family of nuclear genes expressed in photosynthetic and nonphotosynthetic tissues encodes GS polypeptides which are assembled into oligomeric isoenzymes located either in the cytosol or in the plastids (Bernard and Habash, 2009). In poplar, the GS family is organized in four groups of duplicated genes, three of which code for cytosolic GS isoforms (GS1.1, GS1.2 and GS1.3) and one that codes for the plastidic GS isoform (GS2) (Castro-Rodr ıguez et al, 2011). Recent results support that GS gene redundancy may contribute to the homoeostasis of N metabolism in functions associated with changes in glutamine use in multiple metabolic pathways (Castro-Rodriguez et al, 2015).…”