Targeted manipulation of maize genes in vivo using chimeric RNA/DNA oligonucleotides

Site-specific heritable mutations in maize genes were engineered by introdu cing chimeric RNA/DNA oligonucleotides. Two independent targets within the endogenous maize acetohydroxyacid synthase gene sequence were modified in a site-specific fashion, thereby conferring resistance to either imidazolino ne or sulfonylurea herbicides. Similarly, an engineered green fluorescence protein transgene was site-specifically modified in vivo, Expression of the introduced inactive green fluorescence protein was restored, and plants co ntaining the modified transgene were regenerated. Progeny analysis indicate d Mendelian transmission of the converted transgene, The efficiency of gene conversion mediated by chimeric oligonucleotides in maize was estimated as 10(-4), which is 1-3 orders of magnitude higher than frequencies reported for gene targeting by homologous recombination in plants. The heritable cha nges in maize genes engineered by this approach create opportunities for ba sic studies of plant gene function and agricultural trait manipulation and also provide a system for studying mismatch repair mechanisms in maize.