Functional <scp>PPO2</scp> mutations: co‐occurrence in one plant or the same <i>ppo2</i> allele of herbicide‐resistant <scp><i>Amaranthus palmeri</i></scp> in the <scp>US</scp> mid‐south

Noguera, Matheus M.; Rangani, Gulab; Heiser, James W.; Bararpour, Taghi; Steckel, Lawrence E.; Betz, Michael; Porri, Aimone; Lerchl, Jens; Zimmermann, Sophie; Nichols, Robert L.; Roma‐Burgos, Nilda

doi:10.1002/ps.6111

Cited by 18 publications

(17 citation statements)

References 65 publications

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“… 25 Recent publications described the co‐occurrence of diverse PPO mutations in A. tuberculatus and/or A. palmeri populations collected in several US states. 22 , 26 Results show several predominant mutations, as described previously (ΔG210, R128G, and G399A), 25 as well as new mutations and combinations thereof. 22 …”

Section: Introductionsupporting

confidence: 74%

“… 22 , 26 Results show several predominant mutations, as described previously (ΔG210, R128G, and G399A), 25 as well as new mutations and combinations thereof. 22 …”

Section: Introductionsupporting

confidence: 74%

“…It was reported that ΔG210 deletion causes the unravelling of the turn of the PPO2 helix, leading to 50% enlargement in the active site, which can now fit both the substrate and the inhibitor. 24 By contrast, 22 G210 deletion causes a change in the dynamic of the α helix, which becomes more flexible and allows water molecules (solvation) to enter the active site, thus reducing herbicide binding, which in general requires a hydrophobic environment. The principal difference observed between G399 and A399 is the additional methyl group (‐CH3) that creates close repulsive interaction with the central phenyl ring of PPO inhibitors generating repulsive electrostatic interactions that push the herbicide from the binding site.…”

Section: Discussionmentioning

confidence: 99%

“… 21 These R128 substitutions cause loss of the salt bridge interaction between PPO2 and the ligand, reducing herbicide–target affinity. In addition, through modeling prediction, 22 it was shown that R128G, M and L substitutions cause enlargement of the PPO2 active site, which becomes prone to a solvation effect, further reducing ligand–target affinity. A second mutation, a codon deletion resulting in loss of a glycine (ΔG210), in A. tuberculatus and A. palmeri was also shown to confer resistance to several PPO‐inhibiting herbicides including lactofen and fomesafen.…”

Section: Introductionmentioning

confidence: 99%

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Inhibition profile of trifludimoxazin towards PPO2 target site mutations

Porri

Betz

Seebruck

et al. 2022

Pest Management Science

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BACKGROUND Target site resistance to herbicides that inhibit protoporphyrinogen IX oxidase (PPO; EC 1.3.3.4) has been described mainly in broadleaf weeds based on mutations in the gene designated protoporphyrinogen oxidase 2 (PPO2) and in one monocot weed species in protoporphyrinogen oxidase 1 (PPO1). To control PPO target site resistant weeds in future it is important to design new PPO‐inhibiting herbicides that can control problematic weeds expressing mutant PPO enzymes. In this study, we assessed the efficacy of a new triazinone‐type inhibitor, trifludimoxazin, to inhibit PPO2 enzymes carrying target site mutations in comparison with three widely used PPO‐inhibiting herbicides. RESULTS Mutated Amaranthus spp. PPO2 enzymes were expressed in Escherichia coli, purified and measured biochemically for activity and inhibition kinetics, and used for complementation experiments in an E. coli hemG mutant that lacks the corresponding microbial PPO gene function. In addition, we used ectopic expression in Arabidopsis and structural PPO protein modeling to support the enzyme inhibition study. The generated data strongly suggest that trifludimoxazin is a strong inhibitor both at the enzyme level and in transgenics Arabidopsis ectopically expressing PPO2 target site mutations. CONCLUSION Trifludimoxazin is a potent PPO‐inhibiting herbicide that inhibits various PPO2 enzymes carrying target site mutations and could be used as a chemical‐based control strategy to mitigate the widespread occurrence of PPO target site resistance as well as weeds that have evolved resistance to other herbicide mode of actions. © 2022 BASF SE and The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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Section: Introductionsupporting

confidence: 74%

“… 22 , 26 Results show several predominant mutations, as described previously (ΔG210, R128G, and G399A), 25 as well as new mutations and combinations thereof. 22 …”

Section: Introductionsupporting

confidence: 74%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Inhibition profile of trifludimoxazin towards PPO2 target site mutations

Porri

Betz

Seebruck

et al. 2022

Pest Management Science

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“…Resistance to glyphosate and acetolactate synthase (ALS) inhibitors among A. palmeri populations is rampant. A. palmeri has evolved resistance to eight herbicide SOAs including that of protoporphyrinogen oxidase (PPO)-inhibitors (Noguera et al, 2020) and S-metolachlor (Brabham et al, 2019) in the mid-southern US, starting in Arkansas. The increase in resistance to PPO inhibitors forced farmers to rely more on VLCFA inhibitors for A. palmeri control, further reducing the diversity of herbicides and spectrum of control.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Resistance to S-metolachlor in Palmer amaranth

et al. 2021

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Herbicides are major tools for effective weed management. The evolution of resistance to herbicides in weedy species, especially contributed by non-target-site-based resistance (NTSR) is a worrisome issue in crop production globally. Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) is one of the extremely difficult weeds in southern US crop production. In this study, we present the level and molecular basis of resistance to the chloroacetamide herbicide, S-metolachlor, in six field-evolved A. palmeri populations that had survivors at the recommended field-dose (1.1 kg ai ha−1). These samples were collected in 2014 and 2015. The level of resistance was determined in dose-response assays. The effective dose for 50% control (ED50) of the susceptible population was 27 g ai ha−1, whereas the ED50 of the resistant populations ranged from 88 to 785 g ai ha−1. Therefore, A. palmeri resistance to S-metolachlor evolved in Arkansas as early as 2014. Metabolic-inhibitor and molecular assays indicated NTSR in these populations, mainly driven by GSTs. To understand the mechanism of resistance, selected candidate genes were analyzed in leaves and roots of survivors (with 1 × S-metolachlor). Expression analysis of the candidate genes showed that the primary site of S-metolachlor detoxification in A. palmeri is in the roots. Two GST genes, ApGSTU19 and ApGSTF8 were constitutively highly expressed in roots of all plants across all resistant populations tested. The expression of both GSTs increased further in survivors after treatment with S-metolachlor. The induction level of ApGSTF2 and ApGSTF2like by S-metolachlor differed among resistant populations. Overall, higher expression of ApGSTU19, ApGSTF8, ApGSTF2, and ApGSTF2like, which would lead to higher GST activity in roots, was strongly associated with the resistant phenotype. Phylogenetic relationship and analysis of substrate binding site of candidate genes suggested functional similarities with known metolachlor-detoxifying GSTs, effecting metabolic resistance to S-metolachlor in A. palmeri. Resistance is achieved by elevated baseline expression of these genes and further induction by S-metolachlor in resistant plants.

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Can double PPO mutations exist in the same allele and are such mutants functional?

Porri

Noguera

Betz

et al. 2022

Pest Management Science

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BACKGROUND: Resistance to protoporphyrinogen oxidase (PPO)-inhibiting herbicides is endowed primarily by target-site mutations at the PPX2 gene that compromise binding of the herbicide to the catalytic domain. In Amaranthus spp. PPX2, the most prevalent target mutations are deletion of the G210 codon, and the R128G and G339A substitutions. These mutations strongly affect the dynamic of the PPO2 binding pocket, resulting in reduced affinity with the ligand. Here we investigated the likelihood of co-occurrence of the most widespread target site mutations in the same PPX2 allele. RESULTS: Plants carrying R128G+/+ ΔG210+/−, where + indicates presence of the mutation, were crossed with each other. The PPX2 of the offspring was subjected to pyrosequencing and E. coli-based Sanger sequencing to determine mutation frequencies and allele co-occurrence. The data show that R128G ΔG210 can occur in one allele only; the second allele carries only one mutation. Double mutation in both alleles is less likely because of significant loss of enzyme activity. The segregation of offspring populations derived from a cross between heterozygous plants carrying ΔG210 G399A also showed no co-occurrence in the same allele. The offspring exhibited the expected mutation distribution patterns with few exceptions. CONCLUSIONS: Homozygous double-mutants are not physiologically viable. Double-mutant plants can only exist in a heterozygous state. Alternatively, if two mutations are detected in one plant, each mutation would occur in a separate allele.

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Functional PPO2 mutations: co‐occurrence in one plant or the same ppo2 allele of herbicide‐resistant Amaranthus palmeri in the US mid‐south

Cited by 18 publications

References 65 publications

Inhibition profile of trifludimoxazin towards PPO2 target site mutations

Inhibition profile of trifludimoxazin towards PPO2 target site mutations

Mechanism of Resistance to S-metolachlor in Palmer amaranth

Can double PPO mutations exist in the same allele and are such mutants functional?

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