Selectable Marker Gene Removal and Expression of Transgene by Inducible Promoter Containing FFDD Cis-Acting elements in Transgenic Plants

Selectable marker gene (SMG) systems are critical for generation of transgenic crops. Transgenic crop production without using SMG is not economically feasible. However, SMGs are non-essential once an intact transgenic plant has been established. Elimination of SMGs from transgenic crops both increases public acceptance of GM crops and prepares gene stacking possibility for improvement of complex traits. Synthetic inducible promoters provide an efficient and flexible strategy to regulate transgene expression.

This study aimed to construct a transformation vector based on Cre/loxP recombination system to enhance efficiency of SMG-free transgenic plant production followed by post-excision expression of gene of interest in transgenic plants by a pathogen inducible promoter.

In pG-IPFFDD-cre^int-gus^int construct, cre recombinase and selectable marker gene (nptII) cassettes were placed between the two loxP recognition sites in direct orientation. Seed-specific Napin promoter was used for regulation of Cre expression in transgenic seeds. In the construct, loxP flanked sequence containing nptII and recombinase cassettes, located between a pathogen inducible promoter containing FFDD cis-acting elements and β-glucuronidase coding region. The cunstuct was transformed into Nicotiana tabaccum via Agrobacterium-mediated transformation.

The results showed that both cre and nptII excision occurs in T1 progeny tobacco plants through seed-specific cre expression. The excisions were confirmed by methods activation of the gus gene, germination test on kanamycin-containing medium and molecular analysis. Inducibility of gus expression by FFDD-containing promoter in T1 leaf tissues was confirmed by histochemical Gus staining assay.

The established system is not only an efficient tool for marker gene elimination but also provides possibility for inducible expression of the transgene.