title: Heat-shock-mediated elimination of the nptII marker gene in transgenic apple (Malus×domestica Borkh.).
abstract: Production of marker-free genetically modified (GM) plants is one of the major challenges of molecular fruit breeding. Employing clean vector technologies, allowing the removal of undesired DNA sequences from GM plants, this goal can be achieved. The present study describes the establishment of a clean vector system in apple Malus×domestica Borkh., which is based on the use of the neomycin phosphotransferase II gene (nptII) as selectable marker gene and kanamycin/paramomycin as selective agent. The nptII gene can be removed after selection of GM shoots via site-specific excision mediated by heat-shock-inducible expression of the budding yeast FLP recombinase driven by the soybean Gmhsp17.5-E promoter. We created a monitoring vector containing the nptII and the flp gene as a box flanked by two direct repeats of the flp recognition target (FRT) sites. The FRT-flanked box separates the gusA reporter gene from the Cauliflower Mosaic Virus 35S (CaMV 35S) promoter. Consequently, GUS expression does only occur after elimination of the FRT-flanked box. Transformation experiments using the monitoring vector resulted in a total of nine transgenic lines. These lines were investigated for transgenicity by PCR, RT-PCR and Southern hybridization. Among different temperature regimes tested, exposure to 42 °C for 3.5 to 4h led to efficient induction of FLP-mediated recombination and removal of the nptII marker gene. A second round of shoot regeneration from leaf explants led to GM apple plants completely free of the nptII gene.
authors.affiliation: Julius Kühn-Institute-Federal Research Centre for Cultivated Plants, Institute for Breeding Research on Horticultural and Fruit Crops, Pillnitzer Platz 3a, D-01326 Dresden, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Herzog
authors.forename: Henryk
authors.initials: H
authors.lastname: Flachowsky
authors.forename: Holger B
authors.initials: HB
authors.lastname: Deising
authors.forename: Magda-Viola
authors.initials: MV
authors.lastname: Hanke
mesh_terms: D001483:Base Sequence; D001947:Breeding; D004254:DNA Nucleotidyltransferases / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics; D017343:Genes, Plant; D005819:Genetic Markers; D005822:Genetic Vectors; D018869:Heat-Shock Response / Q000235:genetics; D019868:Kanamycin Kinase / Q000235:genetics*; D027845:Malus / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D010303:Paromomycin / Q000494:pharmacology; D018520:Plant Shoots / Q000235:genetics / Q000254:growth & development; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D012038:Regeneration / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics
chemical_list: D017931:DNA Primers; D005819:Genetic Markers; D029701:Saccharomyces cerevisiae Proteins; D010303:Paromomycin; D019868:Kanamycin Kinase; D004254:DNA Nucleotidyltransferases; C045119:FLP recombinase