Novel aspects of glutamine synthetase (GS) regulation revealed by a detailed expression analysis of the entire GS gene family of Medicago truncatulaunder different physiological conditions

BMC Plant Biology

Research Article

Helena G Carvalho¹  Liliana S Silva¹  Ana R Seabra² 

[1]Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180, Porto, Portugal

[2]Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180, Porto, Portugal

[3]Max Planck Group for Fungal Biodiversity, Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Köln, Germany

关键词: Glutamine synthetase;    Nitrogen fixation;    Circadian rhythms;    Medicago truncatula;   

DOI  :  10.1186/1471-2229-13-137

 received in 2013-05-09, accepted in 2013-09-16,  发布年份 2013

来源: Springer

【 摘 要 】

BackgroundGlutamine Synthetase (GS, EC 6.3.1.2) is a central enzyme in nitrogen metabolism, and a key component of nitrogen use efficiency (NUE) and plant yield and thus it is extremely important to understand how it is regulated in plants. Medicago truncatula provides an excellent model system to study GS, as it contain a very simple GS gene family comprising only four expressed genes, MtGS1a and MtGS1b encoding cytosolic polypeptides, and MtGS2a and MtGS2b encoding plastid-located enzymes. To identify new regulatory mechanisms controlling GS activity, we performed a detailed expression analysis of the entire GS gene family of M. truncatula in the major organs of the plant, over a time course of nodule or seed development and during a diurnal cycle.ResultsIndividual GS transcripts were quantified by qRT-PCR, and GS polypeptides and holoenzymes were evaluated by western blot and in-gel activity under native electrophoresis. These studies revealed that all four GS genes are differentially regulated in each organ of the plant, in a developmental manner, and identified new regulatory controls, which appear to be specific to certain metabolic contexts. Studies of the protein profiles showed that the GS polypeptides assemble into organ-specific protein complexes and suffer organ-specific post-translational modifications under defined physiological conditions. Our studies also reveal that GS expression and activity are modulated during a diurnal cycle. The biochemical properties of the four isoenzymes were determined and are discussed in relation to their function in the plant.ConclusionsThis work provides a comprehensive overview of GS expression and regulation in the model legume M. truncatula, contributing to a better understanding of the specific function of individual isoenzymes and to the identification of novel organ-specific post-translational mechanisms of GS regulation. We demonstrate that the GS proteins are modified and/or integrated into protein-complexes that assemble into a specific composition in particular organs of the plant. Taken together, the results presented here open new avenues to explore the regulatory mechanisms controlling GS activity in plants, a subject of major importance due to the crucial importance of the enzyme for plant growth and productivity.

【 授权许可】

Unknown   
© Seabra et al.; licensee BioMed Central Ltd. 2013. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.