Selection of Marker-Free Transgenic Plants Using the Oncogenes (ipt, rol A, B, C) of Agrobacterium as Selectable Markers. In: Jain SM, Minocha SC, editors. Molecular Biology of Woody Plants. Dordrecht: Springer Netherlands; 2000. pp. 25-46. [DOI: 10.1007/978-94-017-2313-8_2]

Generation of selectable marker-free transgenic tomato resistant to drought, cold and oxidative stress using the Cre/loxP DNA excision system

The aim of this research was to generate selectable marker-free transgenic tomato plants with improved tolerance to abiotic stress. An estradiol-induced site-specific DNA excision of a selectable marker gene using the Cre/loxP DNA recombination system was employed to develop transgenic tomato constitutively expressing AtIpk2 beta, an inositol polyphosphate 6-/3-kinase gene from Arabidopsis thaliana. Transgenic tomato plants containing a selectable marker were also produced as controls. The expression of AtIpk2 beta conferred improved resistance to drought, cold and oxidative stress in both sets of transgenic tomato plants. These results demonstrate the feasibility of using this Cre/loxP-based marker elimination strategy to generate marker-free transgenic crops with improved stress tolerance.

Production of marker-free transgenic Nierembergia caerulea using MAT vector system

Agrobacterium tumefaciens strain EHA105 harboring an ipt-type MAT vector, pNPI132, was used to produce morphologically normal transgenic Nierembergia caerulea cv. Mont Blanc employing ipt gene as the selectable marker gene. beta-glucuronidase (GUS) gene was used as model gene of interest. The MAT vector system is a positive selection system that gives the advantage of regeneration to the transgenic cells without killing the non-transgenic cells. Infected explants were cultured on hormone- and antibiotic-free MS medium, and 65% of the regenerated shoots developed ipt shooty phenotype-morphologically abnormal shoots, within approximately 3 months after co-cultivation. Twenty morphologically normal shoots were produced from 12 transgenic ipt shoots 7 months after co-cultivation. The normal shoots rooted well on hormone-free MS medium. Ninety percent of the normal shoots were ipt (-), GUS(+) and excision(+) as determined by PCR and Southern blot analyses. These results indicate that ipt-type MAT vector system can be used successfully in Nierembergia to produce marker-free transgenic plants without using phytohormones and selective chemical agents.

Single-step transformation for generating marker-free transgenic rice using the ipt-type MAT vector system

The ipt-type MAT vector uses the ipt gene for regeneration of marker-free transgenic plants. However, it was pointed out that this system was not suitable for most economically important crops that regenerated through auxin-dependent embryogenesis. We report a single-step transformation system of rice using MAT vector. When we transformed scutellum tissues of 5 days pre-cultured rice seeds, marker-free transgenic rice plants directly regenerated from 25.5% infected scutellum tissues without forming ipt-intermediates within 4 weeks after an infection. Excision of the ipt gene caused the regeneration of marker-free transgenic rice plants through embryogenic tissues. Therefore, this system needs no selective agent and no sexual crossing for identification of transgenic plants not containing a selectable marker gene. This system is highly effective for generation of marker-free transgenic plants in economically important crops.