Efficient evaluation of a gene containment system for poplar through early flowering induction.

The early flowering system HSP::AtFT allowed a fast evaluation of a gene containment system based on the construct PsEND1::barnase-barstar for poplar. Transgenic lines showed disturbed pollen development and sterility. Vertical gene transfer through pollen flow from transgenic or non-native plant species into their crossable natural relatives is a major concern. Gene containment approaches have been proposed to reduce or even avoid gene flow among tree species. However, evaluation of genetic containment strategies for trees is very difficult due to the long-generation times. Early flowering induction would allow faster evaluation of genetic containment in this case. Although no reliable methods were available for the induction of fertile flowers in poplar, recently, a new early flowering approach was developed. In this study, early flowering poplar lines containing the gene construct PsEND1::barnase-barstar were obtained. The PsEND1 promoter was chosen due to its early expression pattern, its versality and efficiency for generation of male-sterile plants fused to the barnase gene. RT-PCRs confirmed barnase gene activity in flowers, and pollen development was disturbed, leading to sterile flowers. The system developed in this study represents a valuable tool for gene containment studies in forest tree species.