Differences in efficacy, resistance mechanism and target protein interaction between two PPO inhibitors in Palmer amaranth (<i>Amaranthus palmeri</i>)

Wu, Changgong; Goldsmith, Michael‐Rock; Pawlak, John A.; Feng, Pengfei; Smith, Stacie; Vilanova, Santiago; Perez‐Jones, Alejandro

doi:10.1017/wsc.2020.4

Cited by 12 publications

(19 citation statements)

References 54 publications

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“…15 Protogen binding to ∆G210 PPO2 was not negatively affected, which is a favorable condition to minimize related fitness costs. 15,16 However, the same cannot be said about G399A. The authors concluded that the additional methyl group from Ala in relation to Gly protruded into the binding-site, creating repulsive interactions towards the inhibitor (and consequently, towards the substrate).…”

Section: Introductionmentioning

confidence: 99%

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

Porri

Roma‐Burgos²

2022

Preprint

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Background: Resistance to PPO-inhibiting herbicides is primarily endowed by target site mutations at the PPO2 gene that compromise binding of the herbicide to the catalytic domain. In Amaranthus ssp. PPO2, 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 ppo2 allele. Results: Plants carrying R128G+/+ ΔG210+/-, where + indicates presence of the mutation, were crossed with each other. The ppo2 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 only in one allele; 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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Section: Introductionmentioning

confidence: 99%

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

Porri

Roma‐Burgos²

2022

Preprint

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“…Higher ED50 values (up to 614 g fomesafen ha −1 ) were estimated for PPO-resistant populations from Kentucky carrying ∆G210 mutation [38]. On the other hand, low ED50 values (from 12.4 to 28.5 g fomesafen ha −1 ) were reported for populations from Tennessee [27]. Even with low ED50 values, these Tennessee populations had survivors when treated with up to 3360 g ha −1 fomesafen.…”

Section: Resistance Level To Fomesafen and Overall Response To Other Foliar-applied Herbicidesmentioning

confidence: 91%

“…Since A. palmeri is dioecious, it is an obligate outcrossing specie; thus, the accumulation of PPO mutations in the same plant via gene flow is expected. Indeed, some survivors of fomesafen treatment harbor ∆G210 + R128G mutations in the same plant [27]. The authors did not report the level of resistance in these plants or if the mutations co-occurred in the same allele.…”

Section: Introductionmentioning

confidence: 97%

PPO2 Mutations in Amaranthus palmeri: Implications on Cross-Resistance

et al. 2021

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In Arkansas, resistance to protoporphyrinogen IX oxidase (PPO)-inhibiting herbicides in Amaranthus palmeri S. Wats. is mainly due to target site mutations. Although A. palmeri PPO-mutations are well investigated, the cross-resistance that each ppo mutant endows to weed populations is not yet well understood. We aimed to evaluate the response of PPO-resistant A. palmeri accessions, harboring the ppo2 mutations ΔG210 and G399A, to multiple PPO-inhibiting herbicides. Six resistant and one susceptible field accessions were subjected to a dose–response assay with fomesafen, and selected survivors from different fomesafen doses were genotyped to characterize the mutation profile. The level of resistance to fomesafen was determined and a cross-resistance assay was conducted with 1 and 2 times the labeled doses of selected PPO herbicides. The accession with higher predicted dose to control 50% of the population (ED50) had a higher frequency of ΔG210-homozygous survivors. Survivors harboring both mutations, and those that were ΔG210-homozygous, incurred less injury at the highest fomesafen rate tested (1120 g ai ha−1). The populations with a high frequency of ΔG210-homozygous survivors, and those with individuals harboring ΔG210 + G399A mutations, exhibited high potential for cross-resistance to other PPO herbicides. The new PPO–herbicide chemistries (saflufenacil, trifludimoxazin) generally controlled the PPO-resistant populations.

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“…It is also possible that as a simplified testing system that focuses on the target organelle of the plants (chloroplast), the leaf-disk assay is more effective in detecting target site-based resistance (TR) than non-target site based resistance (NTR). Interestingly, for the E. indica, B. scoparia, and Amaranthus populations we tested for glyphosate, dicamba, and fomesafen, target-site mutations were the main underlying resistance mechanism (Baerson et al 2002;LeClere et al 2018;Wu et al 2020aWu et al , 2020bYu et al 2015). If NTR mechanisms such as reduced uptake and translocation are involved (Heap and Duke 2018;Sammons and Gaines 2014), the response of the resistant and sensitive plants at the chloroplast/PSII system level might be similar and thus prevent the leaf-disk assay from capturing their differences.…”

Section: Correlation Between F V /F M Values and Herbicide Spray Injuriesmentioning

confidence: 99%

“…A common practice to evaluate the spread of herbicide resistance is to do routine and massive surveys of weed populations from different geographic locations (Evans et al 2016;González-Torralva et al 2020;Westra et al 2019). These surveys have been done solely through time-consuming and labor-intensive greenhouse herbicide efficacy trials or a combination of greenhouse trials with molecular marker assays (Chatham et al 2015;Salas-Perez et al 2017;Schultz et al 2015;Varanasi et al 2018;Wu et al 2020a). A more rapid assay requiring fewer technical skills (e.g., molecular assays) will enable more weed science labs to conduct weed resistance surveys regularly and more efficiently.…”

Section: Introductionmentioning

confidence: 99%

A nondestructive leaf-disk assay for rapid diagnosis of weed resistance to multiple herbicides

Varanasi

Perez‐Jones

2021

Weed Sci

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Weed resistance survey that monitors the spread of resistant weeds has been mainly conducted through time-consuming, labor-intensive and destructive greenhouse herbicide screens. As an alternative, we here introduce a non-destructive leaf disc assay based on chlorophyll fluorescence (Fv/Fm values which measure photosynthesis efficiency) allowing the detection of resistance to both systemic and contact herbicides within ˜48h. Current study validated the assay on detecting resistance to fomesafen, glyphosate, and dicamba in Palmer amaranth (Amaranthus palmeri S. Watson), waterhemp [Amaranthus tuberculatus (Moq.) Sauer], kochia [Bassia scoparia (L.) A.J. Scott] and goosegrass [Eleusine indica (L.) Gaertn.]. Negative correlation between the Fv/Fm values and the spray injury levels was observed in all herbicide-weed combinations at the discriminating doses, except for glyphosate in Amaranthus. The correlation coefficients were -0.41 for fomesafen (10µM, p<0.0001) in Amaranthus, -0.92 for glyphosate in E. indica (250µM, p<0.0001), and -0.44 for dicamba in B. scoparia (800 µM, p=0.0023), respectively. At the population level, the assay clearly separated susceptible from highly resistant populations. However, the assay showed lower sensitivity in distinguishing populations of different resistance levels or separating low resistance from susceptible populations. At the individual plant level, results from the leaf disc assay and whole plant spray tests were concordant in 85.5%, 92.3%, and 71.7% of the plants tested for fomesafen-Amaranthus, glyphosate-Eleusine and dicamba-Bassia, respectively. The assay yielded 1-15% false positive and 6-13% false negative results across herbicides. The current study demonstrated that the leaf disc assay is a useful tool to identify weed resistance. Optimization is needed to improve its sensitivities and expand its usage to more diverse herbicide-weed species combinations.

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Differences in efficacy, resistance mechanism and target protein interaction between two PPO inhibitors in Palmer amaranth (Amaranthus palmeri)

Cited by 12 publications

References 54 publications

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

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

PPO2 Mutations in Amaranthus palmeri: Implications on Cross-Resistance

A nondestructive leaf-disk assay for rapid diagnosis of weed resistance to multiple herbicides

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