Optimization of genetic transformation method for an indica rice (Oryza sativa L.) variety Ratnagiri-711

Abstract

A study for method optimization of Agrobacterium-mediated genetic transformation for insect resistance was carried out for a rice variety Ratnagiri-711 showing better regenerability. Three different cry genes viz. cry1Aabc, cry1Fa1 and cry2Aa with a vector system consisting of the disarmed hyper virulent Agrobacterium tumefaciens strain EHA-105 harboring pBinAR or BinBt3 were used. The respective genes were linked to CaMV35S promoter and nptII gene under control of nos promoter and terminator. Scutellum-derived callus bits and embryonic shoot apical meristem of germinating seeds were used as target tissues for callus-mediated and in planta transformation, respectively. Kanamycin screening and PCR analysis was employed for confirmation of presence of transgene. Among five methods of colonization and co-cultivation tried with three cry genes, a callus-mediated transformation method consisting of 20 minutes colonization and 3 days co-cultivation with cry2Aa gene recorded highest transformation frequency (13.79%) but minimum survival (5.27%). On the contrary, considerable transformation frequency (6.35%) with highest survival (79.42%) was observed in an in planta method employing mild injury to embryonic shoot apical meristem of germinating seeds followed by injection of Agrobacterium having cry2Aa gene followed by 15 minutes colonization and then directly sowing in pots. Among three cry genes used, the gene cry2Aa was found most effective showing more transformation frequency.