title: Cytosolic glutamine synthetase: a target for improvement of crop nitrogen use efficiency?
abstract: Overexpression of the cytosolic enzyme glutamine synthetase 1 (GS1) has been investigated in numerous cases with the goal of improving crop nitrogen use efficiency. However, the outcome has generally been inconsistent. Here, we review possible reasons underlying the lack of success and conclude that GS1 activity may be downregulated via a chain of processes elicited by metabolic imbalances and environmental constraints. We suggest that a pivotal role of GS1 may be related to the maintenance of essential nitrogen (N) flows and internal N sensing during critical stages of plant development. A number of more refined overexpression strategies exploiting gene stacking combined with tissue and cell specific targeting to overcome metabolic bottlenecks are considered along with their potential in relation to new N management strategies.
authors.affiliation: Department of Plant and Environmental Sciences, Plant and Soil Science Section, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
authors.forename: Hanne C
authors.initials: HC
authors.lastname: Thomsen
authors.affiliation: Department of Plant and Environmental Sciences, Plant and Soil Science Section, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
authors.forename: Dennis
authors.initials: D
authors.lastname: Eriksson
authors.affiliation: Department of Plant and Environmental Sciences, Plant and Soil Science Section, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
authors.forename: Inge S
authors.initials: IS
authors.lastname: Møller
authors.affiliation: Department of Plant and Environmental Sciences, Plant and Soil Science Section, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark. Electronic address: jks@plen.ku.dk.
authors.forename: Jan K
authors.initials: JK
authors.lastname: Schjoerring
mesh_terms: D018556:Crops, Agricultural; D003600:Cytosol / Q000201:enzymology; D015870:Gene Expression; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010641:Phenotype; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified
chemical_list: D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen
keywords: glutamine synthetase; nitrogen; nitrogen use efficiency (NUE); overexpression; regulation