title: Effective production of marker-free transgenic strawberry plants using inducible site-specific recombination and a bifunctional selectable marker gene.
abstract: Public concerns about the issue of the environmental safety of genetically modified plants have led to a demand for technologies allowing the production of transgenic plants without selectable (antibiotic resistance) markers. We describe the development of an effective transformation system for generating such marker-free transgenic plants, without the need for repeated transformation or sexual crossing. This system combines an inducible site-specific recombinase for the precise elimination of undesired, introduced DNA sequences with a bifunctional selectable marker gene used for the initial positive selection of transgenic tissue and subsequent negative selection for fully marker-free plants. The described system can be generally applied to existing transformation protocols, and was tested in strawberry using a model vector in which site-specific recombination leads to a functional combination of a cauliflower mosaic virus 35S promoter and a GUS encoding sequence, thereby enabling the histochemical monitoring of recombination events. Fully marker-free transgenic strawberry plants were obtained following two different selection/regeneration strategies.
authors.affiliation: Plant Research International, Wageningen University and Research Centre, PO Box 16, 6700 AA Wageningen, The Netherlands.
authors.forename: Jan G
authors.initials: JG
authors.lastname: Schaart
authors.forename: Frans A
authors.initials: FA
authors.lastname: Krens
authors.forename: Koen T B
authors.initials: KT
authors.lastname: Pelgrom
authors.forename: Odette
authors.initials: O
authors.lastname: Mendes
authors.forename: Gerard J A
authors.initials: GJ
authors.lastname: Rouwendal