title: Redundancy and metabolic function of the glutamine synthetase gene family in poplar.
abstract: BACKGROUND
  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. 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  Taken 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.
authors.affiliation: Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Campus Universitario de Teatinos, Universidad de Málaga, 29071, Málaga, Spain. vavicaro@uma.es.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Castro-Rodríguez
authors.affiliation: Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Campus Universitario de Teatinos, Universidad de Málaga, 29071, Málaga, Spain. aggtez@uma.es.
authors.forename: Angel
authors.initials: A
authors.lastname: García-Gutiérrez
authors.affiliation: Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Campus Universitario de Teatinos, Universidad de Málaga, 29071, Málaga, Spain. rcanas@uma.es.
authors.forename: Rafael A
authors.initials: RA
authors.lastname: Cañas
authors.affiliation: Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Campus Universitario de Teatinos, Universidad de Málaga, 29071, Málaga, Spain. bpascual@uma.es.
authors.forename: Ma Belén
authors.initials: MB
authors.lastname: Pascual
authors.affiliation: Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Campus Universitario de Teatinos, Universidad de Málaga, 29071, Málaga, Spain. cavila@uma.es.
authors.forename: Concepción
authors.initials: C
authors.lastname: Avila
authors.affiliation: Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Campus Universitario de Teatinos, Universidad de Málaga, 29071, Málaga, Spain. canovas@uma.es.
authors.forename: Francisco M
authors.initials: FM
authors.lastname: Cánovas
mesh_terms: D055162:Biocatalysis; D004795:Enzyme Stability; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005974:Glutamate-Ammonia Ligase / Q000235:genetics* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D007834:Lasers; D042282:Microdissection; D008970:Molecular Weight; D005810:Multigene Family; D009584:Nitrogen / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D032107:Populus / Q000201:enzymology* / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis; D013696:Temperature
chemical_list: D007527:Isoenzymes; D010455:Peptides; D012333:RNA, Messenger; D011994:Recombinant Proteins; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen