title: A proteome analysis of freezing tolerance in red clover (Trifolium pratense L.).
abstract: BACKGROUND
  Improvement of freezing tolerance of red clover (Trifolium pratense L.) would increase its persistence under cold climate. In this study, we assessed the freezing tolerance and compared the proteome composition of non-acclimated and cold-acclimated plants of two initial cultivars of red clover: Endure (E-TF0) and Christie (C-TF0) and of populations issued from these cultivars after three (TF3) and four (TF4) cycles of phenotypic recurrent selection for superior freezing tolerance. Through this approach, we wanted to identify proteins that are associated with the improvement of freezing tolerance in red clover.
  
  
  RESULTS
  Freezing tolerance expressed as the lethal temperature for 50 % of the plants (LT50) increased markedly from approximately -2 to -16 °C following cold acclimation. Recurrent selection allowed a significant 2 to 3 °C increase of the LT50 after four cycles of recurrent selection. Two-dimensional difference gel electrophoresis (2D-DIGE) was used to study variations in protein abundance. Principal component analysis based on 2D-DIGE revealed that the largest variability in the protein data set was attributable to the cold acclimation treatment and that the two genetic backgrounds had differential protein composition in the acclimated state only. Vegetative storage proteins (VSP), which are essential nitrogen reserves for plant regrowth, and dehydrins were among the most striking changes in proteome composition of cold acclimated crowns of red clovers. A subset of proteins varied in abundance in response to selection including a dehydrin that increased in abundance in TF3 and TF4 populations as compared to TF0 in the Endure background.
  
  
  CONCLUSIONS
  Recurrent selection performed indoor is an effective approach to improve the freezing tolerance of red clover. Significant improvement of freezing tolerance by recurrent selection was associated with differential accumulation of a small number of cold-regulated proteins that may play an important role in the determination of the level of freezing tolerance.
authors.affiliation: Agriculture and Agri-Food Canada, Québec City, Canada. Annick.Bertrand@agr.gc.ca.
authors.forename: Annick
authors.initials: A
authors.lastname: Bertrand
authors.affiliation: Agriculture and Agri-Food Canada, Québec City, Canada.
authors.forename: Marie
authors.initials: M
authors.lastname: Bipfubusa
authors.affiliation: Agriculture and Agri-Food Canada, Québec City, Canada.
authors.forename: Yves
authors.initials: Y
authors.lastname: Castonguay
authors.affiliation: Agriculture and Agri-Food Canada, Québec City, Canada.
authors.forename: Solen
authors.initials: S
authors.lastname: Rocher
authors.affiliation: Luxembourg Institute of Science and Technology, Belvaux, Luxembourg.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Szopinska-Morawska
authors.affiliation: Agriculture and Agri-Food Canada, Kentville, Canada.
authors.forename: Yousef
authors.initials: Y
authors.lastname: Papadopoulos
authors.affiliation: Luxembourg Institute of Science and Technology, Belvaux, Luxembourg.
authors.forename: Jenny
authors.initials: J
authors.lastname: Renaut
mesh_terms: D000064:Acclimatization; D018533:Biomass; D015536:Down-Regulation; D005615:Freezing; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology*; D020543:Proteome; D012641:Selection, Genetic; D013045:Species Specificity; D029921:Trifolium / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D010940:Plant Proteins; D020543:Proteome
keywords: Cold acclimation; Freezing tolerance; Plant abiotic stress; Proteomic analysis; Recurrent selection; Red clover