Strong activity of FLPe recombinase in rice plants does not correlate with the transmission of the recombined locus to the progeny.

Efficient methods for DNA excision are needed for removing selectable marker genes from transgenic plants. The present work evaluated the enhanced FLP recombinase, FLPe, for excising FLP recombination target ( FRT)-flanked marker genes, and generating marker-free rice lines. Previously, the transient FLPe activity was found to be at least threefold higher on the transgene locus compared to that of FLPwt, the wild-type FLP recombinase. In this study, transgenic plants expressing FLPe were cross-pollinated with the plants harboring FRT site to analyze marker excision in F1 plants, and the transmission of marker-free locus to F2 progeny. The FLPe activity, expressed by the strong promoter (maize ubiquitin-1 gene), efficiently excised FRT-flanked marker gene in rice plants. However, marker excision in F2 progeny was tightly linked with the presence of FLPe gene, suggesting insufficient recombination in the gametophyte. The maize ubiquitin-1 promoter is reportedly active in gametophytic tissue and effective in meiotic transmission of the marker-free locus generated by Cre- lox recombination. Therefore, the observed lack of meiotic transmission in this study is possibly due to the limited efficiency of FLPe recombinase. While the reason for the FLPe inefficiency in the gametophyte is not clear, this work highlights the constraints of FLPe recombinase in generating stable marker-free plant lines through cross-pollination or gene induction methods. [ABSTRACT FROM AUTHOR]