Cre/lox Mediated Marker Gene Excision in Transgenic Crop Plants

Abstract

There are several strategies by which the Cre/lox system (from bacteriophage P1) can be used to remove marker genes from transgenic plants. In all strategies, the marker gene is flanked by directly repeated lox sites, and excision occurs when Cre activity is present. The strategies differ in how Cre function is delivered. In one strategy (referred to as crossing), the plants in which the marker gene is flanked by lox sites can be crossed with plants that express Cre activity. In this case, marker excision occurs in the F1 progeny, followed by loss of the cre gene by genetic segregation in the F2 generation. In another strategy (referred to as autoexcision), the cre gene can be included in the DNA segment that is flanked by lox sites. In this strategy, it is critical that the cre gene be regulated such that expression is activated after the marker gene is no longer needed. The crossing and autoexcision strategies were tested to remove an nptII gene from transgenic maize, wheat, soyabean and cotton. The result showed that both strategies can efficiently and completely remove a marker gene.