Excision of a selective marker in transgenic rice using a novel Cre/<Emphasis Type="Italic">loxP</Emphasis> system controlled by a floral specific promoter

Based on the Cre/loxP system, we have developed a novel marker-free system mediating a direct auto-excision of loxP-flanked marker genes from T₁ transgenic rice without any treatment or further offspring crossing. To achieve this, the floral-specific promoter OsMADS45 was isolated from rice and the expression patterns of OsMADS45 promoter was characterised by using the pOs45:GUS transgenic plants. Furthermore, the binary vector with Cre recombinase under the control of OsMADS45 promoter was constructed and introduced into rice by Agrobacterium-mediated transformation and transgenic rice plants were generated. Southern blot analysis showed that auto-excision of the selective markers occurred in some T₁ progeny of the transgenic plants, suggesting that a high auto-excision frequency can be achieved with our Cre/loxP system. This auto-excision strategy provides an efficient way of removing the selectable marker gene from transgenic rice. Xianquan Bai and Qiuyun Wang contributed equally to the work.