A high-throughput Agrobacterium tumefaciens-mediated transformation system for molecular breeding and functional genomics of rice (Oryza sativa L.)

Agrobacterium tumefaciens-mediated transformation is the preferred method for genetic transformation of rice. Here we provide a comprehensive and high-through-put protocol for Agrobacterium-mediated transformation of rice for generating the large numbers of transgenic plants that are required for functional analysis and for evaluating traits of agronomic importance. In a project designed to produce nitrogen use efficient rice plants, we refined/improved several factors including optimization of conditions for inducing vir genes prior to transformation, infection and co-cultivation medium for better interaction of target tissues with Agrobacterium. These optimizations supported not only the survival of co-cultured calli in high frequency, but also the production of multiple resistant cell lines per co-cultured embryogenic and nodular callus. In addition, improvements in plant tissue culture, selection and regeneration media has enabled us to produce large numbers of transgenic rice plants containing genes of agronomical importance. Partial desiccation and ABA treatment to hygromycin-resistant callus tissue significantly (P<0.05) enhanced both regeneration frequency and regeneration of transgenic plantlets per callus tissue. Regeneration frequency was further improved by optimizing the concentration of copper sulphate in the regeneration medium. The majority of the transgenic plants obtained using this improved protocol displayed a normal phenotype and the gene of interest was inherited by the progeny in a Mendelian fashion. Homozygous plants of selected lines showed stable phenotypes both in soil and hydroponic conditions even after five generations. Availability of such a high-throughput Agrobacterium-mediated transformation system will improve future opportunities for rice genetics and functional genomics study.