Development of simple and efficient in planta transformation method for rice (Oryza sativa L.) using Agrobacterium tumefaciens

Seeds of rice (Oryza sativa L. var. Koshihikari) were soaked in water for 2 d. Thereafter, the embryo containing an apical meristem was inoculated with Agrobacterium tumefaciens by piercing a site of the husk overlying the embryonic apical meristem with a needle that had been dipped in an A. tumefaciens inoculum. The inoculated seeds were then grown to maturation (T0 plants) and allowed to pollinate naturally to set seeds (T1 plants) in pots under nonsterile conditions. To examine the transformation by various means, three different strains of A. tumefaciens were used for transformation: an M-21 mutant, which is an avirulent mutant with a Tn5 insertion in the iaaM gene, and two LBA4404 strains each with a different binary vector. Five different lines of evidence were demonstrated the transformation: the altered phenotype and its inheritance by the next generation, histochemical detection of beta-glucuronidase, resistance to hygromycin B, detection of the transgene by PCR and rescue of a plasmid consisting of the integrated T-DNA and the flanking rice genome DNA. Transformation efficiency of T1 plants was estimated to be 40% and 43% by PCR and a histochemical assay of beta-glucuronidase, respectively.