Abstract:

Cre/lox -mediated gene excision in commercial rice (Oryza sativa L.) plants was studied with a recombination-reporter gene system, in which the selectable marker hygromycin phosphotransferase gene (hpt) flanking by two directly oriented lox sites was located between the rice actin1 promoter and a promoterless gusA gene. This system allows visualization of GUS expression by activating promoterless gusA after site-specific recombination. The crossing strategy was used to introduce the cre gene into the lox plants. In 30 hybrid plants from four crosses made from T₀ actin1 promoter-lox -hpt -lox -gusA plant with T₀ cre plant, 12 expressed GUS and 9 showed hygromycin-sensitive. We furthermore demonstrated the utility of the Cre/lox in excision of hpt marker gene in an elite indica rice restorer Minghui 86 transformed with both insecticidal modified cowpea trypsin inhibitor gene sck and Bacillus thuringiensis endotoxin gene cryIAc. In 77 hybrid plants from nine crosses made from T₂ homozygous lox -hpt -lox -sck -cryIAc plant with T₂ homozygous cre plant, 56 showed hygromycin-sensitive. Molecular analyses confirmed the excision of hpt in all hygromycin-sensitive plants.

Key words: Cre/lox , gene excision, transgenic rice, insect resistance, sck , cryIAc, marker-free