Precise genome modification in the crop species Zea mays using zinc-finger nucleases

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Abstract
The scope for improvement of yield and disease resistance of crop plants by genetic engineering has been limited by the lack of an efficient method for targeted gene modification. Zinc-finger protein technology looks set to fill the gap. This relies on the use of designed zinc-finger nucleases, artificial chimaeric proteins that exploit the natural recognition mechanism of cellular DNA repair machinery, to make sequence-specific double-stranded DNA breaks at a target locus. In this issue two groups report the successful application of this emerging technique. Shukla et al. modify the maize gene IPK1, thereby introducing both herbicide tolerance and modified phytate metabolism into this important crop plant. Townsend et al. target the SuR loci in tobacco plants, conferring resistance to imidazolinone and sulphonylurea herbicides. The method achieves a high frequency of gene targeting and should be suitable for the routine modification of endogenous plant genes. Genetic engineering in plants remains laborious and time consuming, with no precise genetic engineering methods comparable to those available in animal models. A new approach that relies on the use of designed zinc-finger nucleases is showcased here in maize, inducing herbicide tolerance that is stably inherited. Agricultural biotechnology is limited by the inefficiencies of conventional random mutagenesis and transgenesis. Because targeted genome modification in plants has been intractable1, plant trait engineering remains a laborious, time-consuming and unpredictable undertaking. Here we report a broadly applicable, versatile solution to this problem: the use of designed zinc-finger nucleases (ZFNs) that induce a double-stranded break at their target locus2. We describe the use of ZFNs to modify endogenous loci in plants of the crop species Zea mays. We show that simultaneous expression of ZFNs and delivery of a simple heterologous donor molecule leads to precise targeted addition of an herbicide-tolerance gene at the intended locus in a significant number of isolated events. ZFN-modified maize plants faithfully transmit these genetic changes to the next generation. Insertional disruption of one target locus, IPK1, results in both herbicide tolerance and the expected alteration of the inositol phosphate profile in developing seeds. ZFNs can be used in any plant species amenable to DNA delivery; our results therefore establish a new strategy for plant genetic manipulation in basic science and agricultural applications.