title: Metabolic profiling reveals altered sugar and secondary metabolism in response to UGPase overexpression in Populus.
abstract: BACKGROUND
  UDP-glucose pyrophosphorylase (UGPase) is a sugar-metabolizing enzyme (E.C. 2.7.7.9) that catalyzes a reversible reaction of UDP-glucose and pyrophosphate from glucose-1-phosphate and UTP. UDP-glucose is a key intermediate sugar that is channeled to multiple metabolic pathways. The functional role of UGPase in perennial woody plants is poorly understood.
  
  
  RESULTS
  We characterized the functional role of a UGPase gene in Populus deltoides, PdUGPase2. Overexpression of the native gene resulted in increased leaf area and leaf-to-shoot biomass ratio but decreased shoot and root growth. Metabolomic analyses showed that manipulation of PdUGPase2 results in perturbations in primary, as well as secondary metabolism, resulting in reduced sugar and starch levels and increased phenolics, such as caffeoyl and feruloyl conjugates. While cellulose and lignin levels in the cell walls were not significantly altered, the syringyl-to-guaiacyl ratio was significantly reduced.
  
  
  CONCLUSIONS
  These results demonstrate that PdUGPase2 plays a key role in the tightly coupled primary and secondary metabolic pathways and perturbation in its function results in pronounced effects on growth and metabolism beyond cell wall biosynthesis of Populus.
authors.forename: Raja S
authors.initials: RS
authors.lastname: Payyavula
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Tschaplinski
authors.forename: Sara S
authors.initials: SS
authors.lastname: Jawdy
authors.forename: Robert W
authors.initials: RW
authors.lastname: Sykes
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Tuskan
authors.forename: Udaya C
authors.initials: UC
authors.lastname: Kalluri
mesh_terms: D018533:Biomass; D002473:Cell Wall / Q000378:metabolism; D002482:Cellulose / Q000378:metabolism; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D005958:Glucosephosphates / Q000378:metabolism; D008031:Lignin / Q000378:metabolism; D055432:Metabolomics; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D030821:Plants, Genetically Modified; D032107:Populus / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D064210:Secondary Metabolism; D013213:Starch / Q000378:metabolism; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000235:genetics* / Q000378:metabolism
chemical_list: D005958:Glucosephosphates; D010940:Plant Proteins; D002482:Cellulose; D013213:Starch; D008031:Lignin; C031590:glucose-1-phosphate; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase