Generation of Transgene-Free Semidwarf Maize Plants by Gene Editing ofGibberellin-Oxidase20-3Using CRISPR/Cas9

The green revolution gene gibberellin oxidase contributes to the semidwarf phenotype, improving product and lodging resistance. Dissecting the function of GA biosynthetic genes would be helpful for dwarf maize breeding. In this study, we edited the maizeGA20ox3gene and generated semidwarf maize plants using CRISPR/Cas9 technology. Application of exogenous gibberellin can recover the dwarf phenotype, indicating that the mutants are gibberellin deficient. The contents of GA(12)and GA(53)were elevated in the mutants due to the disruption of GA20 oxidase, whereas the contents of other GA precursors (GA(15), GA(24), GA(9), GA(44), and GA(20)) were decreased in the mutants, and the accumulation of bioactive GA(1)and GA(4)was also decreased, contributing to the semidwarf phenotype. Transgene-free dwarf maize was selected from T-2-generation plants and might be useful for maize breeding in the future.