title: Self-excision of the antibiotic resistance gene nptII using a heat inducible Cre-loxP system from transgenic potato.
abstract: Resistance to antibiotics mediated by selectable marker genes remains a powerful selection tool for transgenic event production. However, regulatory agencies and consumer concerns favor these to be eliminated from food crops. Several excision systems exist but none have been optimized or shown to be functional for clonally propagated crops. The excision of the nptII gene conferring resistance to kanamycin has been achieved here using a gene construct based on a heat-inducible cre gene producing a recombinase that eliminates cre and nptII genes flanked by two loxP sites. First-generation regenerants with the Cre-loxP system were obtained by selection on kanamycin media. Following a heat treatment, second generation regenerants were screened for excision by PCR using nptII, cre, and T-DNA borders primers. Excision efficiency appeared to be at 4.7% depending on the heat treatment. The footprint of the excision was shown by sequencing between T-DNA borders to correspond to a perfect recombination event. Selectable marker-free sprouts were also obtained from tubers of transgenic events when submitted to similar heat treatment at 4% frequency. Spontaneous excision was not observed out of 196 regenerants from untreated transgenic explants. Biosafety concerns are minimized because the expression of cre gene driven by the hsp70 promoter of Drosophila melanogaster was remarkably low even under heat activation and no functional loxP site were found in published Solanum sequence database. A new plant transformation vector pCIP54/55 was developed including a multiple cloning site and the self-excision system which should be a useful tool not only for marker genes in potato but for any gene or sequence removal in any plant.
authors.affiliation: Applied Biotechnology Laboratory, Germplasm enhancement and Crop Improvement Division, International Potato Center CIP, P.O. Box 1558, Lima 12, Peru.
authors.forename: Wilmer
authors.initials: W
authors.lastname: Cuellar
authors.forename: Amélie
authors.initials: A
authors.lastname: Gaudin
authors.forename: Dennis
authors.initials: D
authors.lastname: Solórzano
authors.forename: Armando
authors.initials: A
authors.lastname: Casas
authors.forename: Luis
authors.initials: L
authors.lastname: Nopo
authors.forename: Prakash
authors.initials: P
authors.lastname: Chudalayandi
authors.forename: Giuliana
authors.initials: G
authors.lastname: Medrano
authors.forename: Jan
authors.initials: J
authors.lastname: Kreuze
authors.forename: Marc
authors.initials: M
authors.lastname: Ghislain
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003001:Cloning, Molecular; D017931:DNA Primers; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D004351:Drug Resistance / Q000187:drug effects*; D017343:Genes, Plant / Q000187:drug effects*; D005819:Genetic Markers; D010935:Plant Diseases / Q000382:microbiology*; D030821:Plants, Genetically Modified; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic; D011198:Solanum tuberosum / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D017931:DNA Primers; D018744:DNA, Plant; D005819:Genetic Markers