Field-Evolved ΔG210-ppo2 from Palmer Amaranth Confers Pre-emergence Tolerance to PPO-Inhibitors in Rice and Arabidopsis .

Resistance to protoporphyrinogen IX oxidase (PPO)-inhibitors in Amaranthus palmeri and Amaranthus tuberculatus is mainly contributed by mutations in the PPO enzyme, which renders herbicide molecules ineffective. The deletion of glycine210 ( ΔG210 ) is the most predominant PPO mutation. ΔG210-ppo2 is overexpressed in rice ( Oryza sativa c. 'Nipponbare') and Arabidopsis thaliana (Col-0). A foliar assay was conducted on transgenic T 1 rice plants with 2× dose of fomesafen (780 g ha -1 ), showing less injury than the non-transgenic (WT) plants. A soil-based assay conducted with T 2 rice seeds confirmed tolerance to fomesafen applied pre-emergence. In agar medium, root growth of WT rice seedlings was inhibited >90% at 5 µM fomesafen, while root growth of T2 seedlings was inhibited by 50% at 45 µM fomesafen. The presence and expression of the transgene were confirmed in the T 2 rice survivors of soil-applied fomesafen. A soil-based assay was also conducted with transgenic A. thaliana expressing ΔG210-ppo2 which confirmed tolerance to the pre-emergence application of fomesafen and saflufenacil. The expression of A. palmeri   ΔG210-ppo2 successfully conferred tolerance to soil-applied fomesafen in rice and Arabidopsis. This mutant also confers cross-tolerance to saflufenacil in Arabidopsis. This trait could be introduced into high-value crops that lack chemical options for weed management.