Creation of herbicide-tolerant crops by gene targeting

Herbicide-tolerant crops including glyphosate-tolerant crops, generated via transgenic approaches are now cultivated widely. However, only a few varieties of transgenic herbicide-tolerant crops have been commercialized due to the time and cost required to obtain regulatory clearance. In contrast, herbicide-tolerant crops resulting from mutagenesis approaches are less problematic. However, the low occurrence of spontaneous mutations at the required sequence in the target locus continues to limit this approach. A promising alternative for inducing desirable mutations in endogenous plant genomes is homologous recombination (HR)-dependent gene targeting (GT). Here, we review three different approaches to create herbicide-tolerant plants, i.e., transgenic approaches, mutagenesis and HR-dependent GT. Among these techniques, HR-dependent GT is relatively new. We introduce the basic mechanism of HR-dependent GT, present an example of how to construct herbicide-tolerant rice plants by this method, and suggest candidate genes that could be targeted to confer herbicide tolerance by HR-dependent GT. (C) Pesticide Science Society of Japan