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

Abstract

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 T1 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 T2 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 T2 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.

Molecular Mechanisms of Herbicide Resistance in Weeds

“…Among grasses, Echinochloa ssp. is reported in two articles [ 9 , 14 ] and L. multiflorum in one [ 8 ]; among dicots, two articles reported on the global invasive weed species A. palmeri [ 10 , 13 ]. All these weeds are acknowledged to be among the top 10 weed species resistant to most SoAs globally [ 19 ].…”

“…Interestingly, information on the resistance to auxins in Echinochloa ssp. [ 14 ], microtubule assembly [ 13 ], and PPO inhibitors [ 10 ], both in A. palmeri , are contributions of this Special Issue.…”

“…Three articles reported mechanisms of TSR nature covering most of the known types: point mutations [ 8 , 9 ], codon deletion [ 10 ], and altered expression patterns [ 9 ].…”

“…Resistance to protoporphyrinogen oxidase (PPO) inhibitors in Amaranthus palmeri is mainly contributed by the deletion of glycine210 codon (ΔG210), which renders herbicide molecules ineffective [ 11 ]. A contribution to this Special Issue functionally validated this codon deletion in other plant species, showing that when ΔG210-PPO was overexpressed in rice and Arabidopsis thaliana , it conferred tolerance to fomesafen applied pre-emergence and cross-tolerance to saflufenacil in A. thaliana [ 10 ]. Moreover, the expression of A. palmeri ΔG210-PPO2 also conferred tolerance to fomesafen in rice and A. thaliana when soil-applied, together with cross-tolerance to saflufenacil in Arabidopsis [ 10 ].…”

“…A contribution to this Special Issue functionally validated this codon deletion in other plant species, showing that when ΔG210-PPO was overexpressed in rice and Arabidopsis thaliana , it conferred tolerance to fomesafen applied pre-emergence and cross-tolerance to saflufenacil in A. thaliana [ 10 ]. Moreover, the expression of A. palmeri ΔG210-PPO2 also conferred tolerance to fomesafen in rice and A. thaliana when soil-applied, together with cross-tolerance to saflufenacil in Arabidopsis [ 10 ]. This tolerance trait to PPO inhibitors could be introduced into crops for weed management and herbicide resistance alleviation.…”