Single-copy primary transformants of maize obtained through the co-introduction of a recombinase-expressing construct

We describe a variation of the method to generate single-copy transgenic pl ants by recombinase-mediated resolution of multiple insertions. In this stu dy, a transgene construct flanked by oppositely oriented lox sites was co-b ombarded into maize cells along with a cre-expressing construct. From analy sis of the regenerated plants, a high percentage of the primary transforman ts harbored a single copy of the introduced transgene, and among these, a m ajority also lacked the cre construct. We deduce that the expression of cre must have contributed to resolving concatemeric molecules either prior to or after DNA integration into the maize genome.