Transgene excision in pollen using a codon optimized serine resolvase CinH-RS2 site-specific recombination system

Transgene escape, a major environmental and regulatory concern in transgenic crop cultivation, could be alleviated by removing transgenes from pollen, the most frequent vector for transgene flow. A transgene excision vector containing a codon optimized serine resolvase CinH recombinase (CinH) and its recognition sites RS2 were constructed and transformed into tobacco (Nicotiana tabacum cv. Xanthi). CinH recombinase recognized 119 bp of nucleic acid sequences, RS2, in pollen and excised the transgene flanked by the RS2 sites. In this system, the pollen-specific LAT52 promoter from tomato was employed to control the expression of CinH recombinase. Loss of expression of a green fluorescent protein (GFP) gene under the control of the LAT59 promoter from tomato was used as an indicator of transgene excision. Efficiency of transgene excision from pollen was determined by flow cytometry (FCM)-based pollen screening. While a transgenic event in the absence of CinH recombinase contained about 70% of GFP-synthesizing pollen, three single-copy transgene events contained less than 1% of GFP-synthesizing pollen based on 30,000 pollen grains analyzed per event. This suggests that CinH-RS2 recombination system could be effectively utilized for transgene biocontainment.