title: Characterization and isolation of a T-DNA tagged banana promoter active during in vitro culture and low temperature stress.
abstract: BACKGROUND
  Next-generation transgenic plants will require a more precise regulation of transgene expression, preferably under the control of native promoters. A genome-wide T-DNA tagging strategy was therefore performed for the identification and characterization of novel banana promoters. Embryogenic cell suspensions of a plantain-type banana were transformed with a promoterless, codon-optimized luciferase (luc+) gene and low temperature-responsive luciferase activation was monitored in real time.
  
  
  RESULTS
  Around 16,000 transgenic cell colonies were screened for baseline luciferase activity at room temperature 2 months after transformation. After discarding positive colonies, cultures were re-screened in real-time at 26 degrees C followed by a gradual decrease to 8 degrees C. The baseline activation frequency was 0.98%, while the frequency of low temperature-responsive luciferase activity was 0.61% in the same population of cell cultures. Transgenic colonies with luciferase activity responsive to low temperature were regenerated to plantlets and luciferase expression patterns monitored during different regeneration stages. Twenty four banana DNA sequences flanking the right T-DNA borders in seven independent lines were cloned via PCR walking. RT-PCR analysis in one line containing five inserts allowed the identification of the sequence that had activated luciferase expression under low temperature stress in a developmentally regulated manner. This activating sequence was fused to the uidA reporter gene and back-transformed into a commercial dessert banana cultivar, in which its original expression pattern was confirmed.
  
  
  CONCLUSIONS
  This promoter tagging and real-time screening platform proved valuable for the identification of novel promoters and genes in banana and for monitoring expression patterns throughout in vitro development and low temperature treatment. Combination of PCR walking techniques was efficient for the isolation of candidate promoters even in a multicopy T-DNA line. Qualitative and quantitative GUS expression analyses of one tagged promoter in a commercial cultivar demonstrated a reproducible promoter activity pattern during in vitro culture. Thus, this promoter could be used during in vitro selection and generation of commercial transgenic plants.
authors: Laboratory of Tropical Crop Improvement, Division of Crop Biotechnics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 13, B-3001 Leuven, Belgium. efren.santos@gmail.com
authors: Efrén
authors: E
authors: Santos
authors: Serge
authors: S
authors: Remy
authors: Els
authors: E
authors: Thiry
authors: Saskia
authors: S
authors: Windelinckx
authors: Rony
authors: R
authors: Swennen
authors: László
authors: L
authors: Sági
mesh_terms: D018929:Cell Culture Techniques; D002478:Cells, Cultured; D003080:Cold Temperature; D004269:DNA, Bacterial / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D017930:Genes, Reporter; D028521:Musa / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012038:Regeneration; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014170:Transformation, Genetic
chemical_list: D004269:DNA, Bacterial; D018744:DNA, Plant; C036483:T-DNA