Abstract
We created a novel herbicide-tolerant rice by gene targeting-mediated introduction of point mutations in acetolactate synthase (ALS) gene. Gene targeting rice homozygous for the modified ALS locus showed hyper tolerance to ALS inhibiting herbicide, bispyribac (BS) as compared to BS tolerant plants produced by a conventional transgenic system. This result indicates that exclusion of the BS sensitive wild-type ALS allele is important to confer high levels of BS tolerance. Interestingly, not only selectable two point mutations, which confer BS tolerance but also non-selectable silent mutations on the targeting vector were incorporated into the gene targeting plants. Furthermore, point mutations on the targeting vector were incorporated into the genome with a mosaic manner in 3 plants out of 70 gene targeting plants, suggesting the involvement of DNA mismatch repair system in the course of T-DNA mediated gene targeting in these 3 plants.
