Molecular confirmation of resistance to PPO inhibitors in Amaranthus tuberculatus and Amaranthus palmeri, and isolation of the G399A PPO2 substitution in A. palmeri

2020 ◽  
pp. 1-7
Author(s):  
Jacob S. Montgomery ◽  
Darci A. Giacomini ◽  
Patrick J. Tranel
Keyword(s):  
Goodness Of Fit ◽  
Resistance Mechanism ◽  
Amino Acid Position ◽  
Resistance Mechanisms ◽  
Palmer Amaranth ◽  
Target Site ◽  
Coding Region ◽  
Common Waterhemp ◽  
Growing Seasons ◽  
Target Site Resistance

Abstract During the 2017 to 2019 growing seasons, samples of waterhemp and Palmer amaranth that had reportedly survived field-rate applications of protoporphyrinogen oxidase (PPO)–inhibiting herbicides were collected from the American Midwest and tested for target-site mutations known at the time to confer resistance. Target-site resistance was identified in nearly all (135 of 145) tested common waterhemp populations but in only 8 of 13 Palmer amaranth populations. Follow-up research on one population of Palmer amaranth (W-8), which tested negative for all such mutations, confirmed it was resistant to lactofen, with a magnitude of resistance comparable to that conferred by the ΔG210 PPO2 mutation. Gene sequences from both isoforms of PPO (PPO1 and PPO2) were compared between W-8 and known PPO inhibitor–sensitive sequence. A glycine-to-alanine substitution at the 399th amino acid position (G399A) of PPO2, recently identified to reduce target-site herbicide sensitivity, was observed in a subset of resistant W-8 plants. Because no missense mutation completely delimited resistant and sensitive sequences, we initially suspected the presence of a secondary, non-target-site resistance mechanism in this population. To isolate G399A, a segregating F2 population was produced and screened with a delimiting rate of lactofen. χ2 goodness-of-fit analysis of dead/alive ratings indicated single-locus inheritance of resistance in the F2 population, and molecular markers for the W-8 parental PPO2 coding region co-segregated tightly, but not perfectly, with resistance. More research is needed to fully characterize Palmer amaranth PPO inhibitor–resistance mechanisms, which appear to be more diverse than those found in common waterhemp.

scholarly journals A Statewide Survey of PPO-Inhibitor Resistance and the Prevalent Target-Site Mechanisms in Palmer amaranth (Amaranthus palmeri) Accessions from Arkansas

Weed Science ◽  
2017 ◽  
Vol 66 (2) ◽  
pp. 149-158 ◽  
Author(s):  
Vijay K. Varanasi ◽  
Chad Brabham ◽  
Jason K. Norsworthy ◽  
Haozhen Nie ◽  
Bryan G. Young ◽  
...  
Keyword(s):  
Resistance Mechanism ◽  
Acetolactate Synthase ◽  
Resistance Mechanisms ◽  
Palmer Amaranth ◽  
Target Site ◽  
Evolution Of Resistance ◽  
Target Site Resistance ◽  
Novel Target ◽  
Als Inhibitors ◽  
Inhibitor Resistance

Palmer amaranth is one of the most problematic weeds in the midsouthern United States, and the evolution of resistance to protoporphyrinogen oxidase (PPO) inhibitors in biotypes already resistant to glyphosate and acetolactate synthase (ALS) inhibitors is a major cause of concern to soybean and cotton growers in these states. A late-season weed-escape survey was conducted in the major row crop–producing counties (29 counties) to determine the severity of PPO-inhibitor resistance in Arkansas. A total of 227 Palmer amaranth accessions were sprayed with fomesafen at 395 g ha−1to identify putative resistant plants. A TaqMan qPCR assay was used to confirm the presence of the ΔG210 codon deletion or the R128G/M (homologous to R98 mutation in common ragweed) target-site resistance mechanisms in thePPX2gene. Out of the 227 accessions screened, 44 were completely controlled with fomesafen, and 16 had only one or two severely injured plants (≥98% mortality) when compared with the 1986 susceptible check (100% mortality). The remaining 167 accessions were genotypically screened, and 82 (49%) accessions were found to harbor the ΔG210 deletion in thePPX2gene. The R128G was observed in 47 (28%) out of the 167 accessions screened. The mutation R128M, on the other hand was rare, found in only three accessions. About 13% of the accessions were segregating for both the ΔG210 and R128G mutations. Sixteen percent of the tested accessions had mortality ratings <90% and did not test positive for the ΔG210 or the R128G/M resistance mechanisms, indicating that a novel target or non–target site resistance mechanism is likely. Overall, PPO inhibitor–resistant Palmer amaranth is widespread in Arkansas, and the ΔG210 resistance mechanism is especially dominant in the northeast corridor, while the R128G mutation is more prevalent in counties near Memphis, TN.

Evolution of target and non-target based multiple herbicide resistance in a single Palmer amaranth (Amaranthus palmeri) population from Kansas

2020 ◽  
Vol 34 (3) ◽  
pp. 447-453
Author(s):  
Sushila Chaudhari ◽  
Vijay K. Varanasi ◽  
Sridevi Nakka ◽  
Prasanta C. Bhowmik ◽  
Curtis R. Thompson ◽  
...  
Keyword(s):  
Resistance Mechanism ◽  
Acetolactate Synthase ◽  
Palmer Amaranth ◽  
Target Site ◽  
Epsp Synthase ◽  
High Incidence ◽  
Evolution Of Resistance ◽  
Target Site Resistance ◽  
Herbicide Atrazine ◽  
Sites Of Action

AbstractThe evolution of resistance to multiple herbicides in Palmer amaranth is a major challenge for its management. In this study, a Palmer amaranth population from Hutchinson, Kansas (HMR), was characterized for resistance to inhibitors of photosystem II (PSII) (e.g., atrazine), acetolactate synthase (ALS) (e.g., chlorsulfuron), and EPSP synthase (EPSPS) (e.g., glyphosate), and this resistance was investigated. About 100 HMR plants were treated with field-recommended doses (1×) of atrazine, chlorsulfuron, and glyphosate, separately along with Hutchinson multiple-herbicide (atrazine, chlorsulfuron, and glyphosate)–susceptible (HMS) Palmer amaranth as control. The mechanism of resistance to these herbicides was investigated by sequencing or amplifying the psbA, ALS, and EPSPS genes, the molecular targets of atrazine, chlorsulfuron, and glyphosate, respectively. Fifty-two percent of plants survived a 1× (2,240 g ai ha−1) atrazine application with no known psbA gene mutation, indicating the predominance of a non–target site resistance mechanism to this herbicide. Forty-two percent of plants survived a 1× (18 g ai ha−1) dose of chlorsulfuron with proline197serine, proline197threonine, proline197alanine, and proline197asparagine, or tryptophan574leucine mutations in the ALS gene. About 40% of the plants survived a 1× (840 g ae ha−1) dose of glyphosate with no known mutations in the EPSPS gene. Quantitative PCR results revealed increased EPSPS copy number (50 to 140) as the mechanism of glyphosate resistance in the survivors. The most important finding of this study was the evolution of resistance to at least two sites of action (SOAs) (~50% of plants) and to all three herbicides due to target site as well as non–target site mechanisms. The high incidence of individual plants with resistance to multiple SOAs poses a challenge for effective management of this weed.

scholarly journals Target-Site Resistances to ALS and PPO Inhibitors Are Linked in Waterhemp (Amaranthus tuberculatus)

Weed Science ◽  
2016 ◽  
Vol 65 (1) ◽  
pp. 4-8 ◽  
Author(s):  
Patrick J. Tranel ◽  
Chenxi Wu ◽  
Ahmed Sadeque
Keyword(s):  
Resistance Mechanism ◽  
Acetolactate Synthase ◽  
Resistance Mechanisms ◽  
Target Site ◽  
Recurrent Parent ◽  
Common Waterhemp ◽  
Independent Assortment ◽  
Resistance Evolution ◽  
Amaranthus Tuberculatus ◽  
Molecular Marker Analysis

It is generally expected that, in the case of multiple herbicide resistance, different resistance mechanisms within a weed will follow Mendel’s law of independent assortment. Research was conducted to investigate anecdotal observations suggesting that target site–based resistances to inhibitors of acetolactate synthase (ALS) and protoporphyrinogen oxidase (PPO) did not follow independent assortment in common waterhemp. Cosegregation of the two resistances was observed in backcross lines (population sensitive to both herbicides as recurrent parent). Specifically, whereas 52% of backcross plants were resistant to a PPO inhibitor, this percentage increased to 92% when the backcross plants were preselected for resistance to an ALS inhibitor. Molecular marker analysis confirmed that the corresponding genes (ALSandPPX2) were genetically linked. When data from all plants analyzed were pooled, the genetic distance between the two genes was calculated to be 7.5 cM. The two genes were found to be about 195 kb apart in the recently published grain amaranth genome, explaining the observed genetic linkage. There is likely enough recombination that occurs between the linked genes to prevent the linkage from having significant implications in terms of resistance evolution. Nevertheless, documentation of the happenstance linkage between target-site genes for resistance to ALS and PPO inhibitors in waterhemp is a reminder that one should not assume distinct resistance mechanism will independently assort.

Target-site resistance to cyhalofop-butyl in bearded sprangletop (Diplachne fusca) from China

Weed Science ◽  
2019 ◽  
Vol 67 (05) ◽  
pp. 534-538 ◽  
Author(s):  
Shuzhong Yuan ◽  
Yingjie Di ◽  
Yueyang Chen ◽  
Yongrui Chen ◽  
Jingxuan Cai ◽  
...  
Keyword(s):  
Amino Acid Position ◽  
Resistance Mechanisms ◽  
Target Site ◽  
Annual Grass ◽  
Site Mutation ◽  
Resistance Level ◽  
First Case ◽  
Resistant Population ◽  
Target Site Resistance ◽  
Grass Weed

AbstractBearded sprangletop [Diplachne fusca(L.) P. Beauv. ex Roem. &amp; Schult. ssp.fascicularis(Lam.) P. M. Peterson &amp; N. Snow] is a noxious annual grass weed of paddy fields, distributed in coastal regions of the Jiangsu and Hebei provinces in China. Cyhalofop-butyl has been widely used to control grass weeds since 2006 in China. Overreliance on cyhalofop-butyl has led to the evolution of resistant weeds. In this study, the resistance level and cyhalofop-butyl resistance mechanisms were investigated in the putative resistant (JSHH) population. The dose–response experiments showed that the JSHHD.fuscapopulation had evolved 8.9-fold resistance to cyhalofop-butyl. Acetyl-CoA carboxylase (ACCase) sequencing revealed a point mutation (GGC to GCC) at amino acid position 2096, resulting in a Gly-2096-Ala substitution in the resistant population. To our knowledge, this is the first case of cyhalofop-butyl resistance inD.fuscaand the first report of a target-site mutation conferring resistance to ACCase-inhibiting herbicides inD.fusca. In addition, the resistantD.fuscapopulation (JSHH) with the Gly-2096-Ala mutation was cross-resistant to the aryloxyphenoxypropionate herbicide metamifop, the cyclohexanedione herbicide sethoxydim, and the phenylpyrazolin herbicide pinoxaden.

scholarly journals A high diversity of mechanisms endows ALS-inhibiting herbicide resistance in the invasive common ragweed (Ambrosia artemisiifolia L.)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ingvild Loubet ◽  
Laëtitia Caddoux ◽  
Séverine Fontaine ◽  
Séverine Michel ◽  
Fanny Pernin ◽  
...  
Keyword(s):  
Resistance Mechanism ◽  
Resistance Management ◽  
Genotyping By Sequencing ◽  
Ambrosia Artemisiifolia ◽  
Target Site ◽  
Major Type ◽  
Common Ragweed ◽  
Resistance Evolution ◽  
Arable Weed ◽  
Target Site Resistance

AbstractAmbrosia artemisiifolia L. (common ragweed) is a globally invasive, allergenic, troublesome arable weed. ALS-inhibiting herbicides are broadly used in Europe to control ragweed in agricultural fields. Recently, ineffective treatments were reported in France. Target site resistance (TSR), the only resistance mechanism described so far for ragweed, was sought using high-throughput genotyping-by-sequencing in 213 field populations randomly sampled based on ragweed presence. Additionally, non-target site resistance (NTSR) was sought and its prevalence compared with that of TSR in 43 additional field populations where ALS inhibitor failure was reported, using herbicide sensitivity bioassay coupled with ALS gene Sanger sequencing. Resistance was identified in 46 populations and multiple, independent resistance evolution demonstrated across France. We revealed an unsuspected diversity of ALS alleles underlying resistance (9 amino-acid substitutions involved in TSR detected across 24 populations). Remarkably, NTSR was ragweed major type of resistance to ALS inhibitors. NTSR was present in 70.5% of the resistant plants and 74.1% of the fields harbouring resistance. A variety of NTSR mechanisms endowing different resistance patterns evolved across populations. Our study provides novel data on ragweed resistance to herbicides, and emphasises that local resistance management is as important as mitigating gene flow from populations where resistance has arisen.

Functional Genomics Analysis of Horseweed (Conyza canadensis) with Special Reference to the Evolution of Non–Target-Site Glyphosate Resistance

Weed Science ◽  
2010 ◽  
Vol 58 (2) ◽  
pp. 109-117 ◽  
Author(s):  
Joshua S. Yuan ◽  
Laura L. G. Abercrombie ◽  
Yongwei Cao ◽  
Matthew D. Halfhill ◽  
Xin Zhou ◽  
...  
Keyword(s):  
Functional Genomics ◽  
Molecular Mechanisms ◽  
Glyphosate Resistance ◽  
Resistance Mechanisms ◽  
Target Site ◽  
Environmentally Benign ◽  
Conyza Canadensis ◽  
Target Site Resistance ◽  
Weedy Species ◽  
Heterologous Microarray

The evolution of glyphosate resistance in weedy species places an environmentally benign herbicide in peril. The first report of a dicot plant with evolved glyphosate resistance was horseweed, which occurred in 2001. Since then, several species have evolved glyphosate resistance and genomic information about nontarget resistance mechanisms in any of them ranges from none to little. Here, we report a study combining iGentifier transcriptome analysis, cDNA sequencing, and a heterologous microarray analysis to explore potential molecular and transcriptomic mechanisms of nontarget glyphosate resistance of horseweed. The results indicate that similar molecular mechanisms might exist for nontarget herbicide resistance across multiple resistant plants from different locations, even though resistance among these resistant plants likely evolved independently and available evidence suggests resistance has evolved at least four separate times. In addition, both the microarray and sequence analyses identified non–target-site resistance candidate genes for follow-on functional genomics analysis.

Target and Non–target site Mechanisms Confer Resistance to Glyphosate in Canadian Accessions ofConyza canadensis

Weed Science ◽  
2017 ◽  
Vol 66 (2) ◽  
pp. 234-245 ◽  
Author(s):  
Eric R. Page ◽  
Christopher M. Grainger ◽  
Martin Laforest ◽  
Robert E. Nurse ◽  
Istvan Rajcan ◽  
...  
Keyword(s):  
Ssr Markers ◽  
Resistance Mechanisms ◽  
Target Site ◽  
Conyza Canadensis ◽  
Weed Species ◽  
Target Site Resistance ◽  
Selection For ◽  
Simple Sequence ◽  
Growing Region ◽  
Selection Of

Glyphosate-resistant populations ofConyza canadensishave been spreading at a rapid rate in Ontario, Canada, since first being documented in 2010. Determining the genetic relationship among existing Ontario populations is necessary to understand the spread and selection of the resistant biotypes. The objectives of this study were to: (1) characterize the genetic variation ofC. canadensisaccessions from the province of Ontario using simple sequence repeat (SSR) markers and (2) investigate the molecular mechanism (s) conferring resistance in these accessions. Ninety-eightC. canadensisaccessions were genotyped using 8 SSR markers. Germinable accessions were challenged with glyphosate to determine their dose response, and the sequences of 5-enolpyruvylshikimate-3-phosphate synthase genes 1 and 2 were obtained. Results indicate that a majority of glyphosate-resistant accessions from Ontario possessed a proline to serine substitution at position 106, which has previously been reported to confer glyphosate resistance in other crop and weed species. Accessions possessing this substitution demonstrated notably higher levels of resistance than non–target site resistant (NTSR) accessions from within or outside the growing region and were observed to form a subpopulation genetically distinct from geographically proximate glyphosate-susceptible and NTSR accessions. Although it is unclear whether other non–target site resistance mechanisms are contributing to the levels of resistance observed in target-site resistant accessions, these results indicate that, at a minimum, selection for Pro-106-Ser has occurred in addition to selection for non–target site resistance and has significantly enhanced the levels of resistance to glyphosate inC. canadensisaccessions from Ontario.

Distribution and validation of genotypic and phenotypic glyphosate and PPO-nhibitor resistance in Palmer amaranth (Amaranthus palmeri) from southwestern Nebraska

2020 ◽  
pp. 1-12 ◽  
Author(s):  
Maxwel C Oliveira ◽  
Darci A Giacomini ◽  
Nikola Arsenijevic ◽  
Gustavo Vieira ◽  
Patrick J Tranel ◽  
...  
Keyword(s):  
Cluster Analysis ◽  
Gene Amplification ◽  
Cropping Systems ◽  
Resistance Mechanism ◽  
Geographic Area ◽  
Glyphosate Resistance ◽  
Resistance Mechanisms ◽  
Palmer Amaranth ◽  
Resistance Evolution ◽  
Inhibitor Resistance

Abstract Failure to control Palmer amaranth with glyphosate and protoporphyrinogen IX oxidase (PPO)-inhibitor herbicides was reported across southwestern Nebraska in 2017. The objectives of this study were to 1) confirm and 2) validate glyphosate and PPO-inhibitor (fomesafen and lactofen) resistance in 51 Palmer amaranth accessions from southwestern Nebraska using genotypic and whole-plant phenotypic assay correlations and cluster analysis, and 3) determine which agronomic practices might be influencing glyphosate resistance in Palmer amaranth accessions in that location. Based on genotypic assay, 88% of 51 accessions contained at least one individual with amplification (>2 copies) of the 5-enolypyruvyl-shikimate-3-phosphate synthase (EPSPS) gene, which confers glyphosate resistance; and/or a mutation in the PPX2 gene, either ΔG210 or R128G, which endows PPO-inhibitor resistance in Palmer amaranth. Cluster analysis and high correlation (0.83) between genotypic and phenotypic assays demonstrated that EPSPS gene amplification is the main glyphosate resistance mechanism in Palmer amaranth accessions from southwestern Nebraska. In contrast, there was poor association between genotypic and phenotypic responses for PPO-inhibitor resistance, which was attributed to segregation for PPO-inhibitor resistance within these accessions and/or the methodology that was adopted herein. Genotypic assays can expedite the process of confirming known glyphosate and PPO-inhibitor resistance mechanisms in Palmer amaranth from southwestern Nebraska and other locations. Phenotypic assays are also a robust method for confirming glyphosate resistance but not necessarily PPO-inhibitor resistance in Palmer amaranth. Moreover, random forest analysis of glyphosate resistance in Palmer amaranth indicated that EPSPS gene amplification, county, and current and previous crops are the main factors influencing glyphosate resistance within that geographic area. Most glyphosate-susceptible Palmer amaranth accessions were found in a few counties in areas with high crop diversity. Results presented here confirm the spread of glyphosate resistance and PPO-inhibitor resistance in Palmer amaranth accessions from southwestern Nebraska and demonstrate that less diverse cropping systems are an important driver of herbicide resistance evolution in Palmer amaranth.

scholarly journals Some approaches to new antibacterial agents

2007 ◽  
Vol 79 (12) ◽  
pp. 2143-2153 ◽  
Author(s):  
John B. Bremner
Keyword(s):  
Bacterial Resistance ◽  
Efflux Pump ◽  
Transmembrane Protein ◽  
Resistance Mechanism ◽  
Resistance Mechanisms ◽  
Target Site ◽  
Resistant Bacteria ◽  
General Strategy ◽  
Dual Action ◽  
Hybrid Drugs

Bacteria use a number of resistance mechanisms to counter the antibacterial challenge, and one of these is the expression of transmembrane protein-based efflux pumps which can pump out antibacterials from within the cells, thus lowering the antibacterial concentration to nonlethal levels. For example, in S. aureus, the NorA pump can pump out the antibacterial alkaloid berberine and ciprofloxacin. One general strategy to reduce the health threat of resistant bacteria is to block a major bacterial resistance mechanism at the same time as interfering with another bacterial pathway or target site. New developments of this approach in the context of dual-action prodrugs and dual-action (or hybrid) drugs in which one action is targeted at blocking the NorA efflux pump and the second action at an alternative bacterial target site (or sites) for the antibacterial action are discussed. The compounds are based on a combination of 2-aryl-5-nitro-1H-indole derivatives (as the NorA efflux pump blocking component) and derivatives of berberine. General design principles, syntheses, antibacterial testing, and preliminary work on modes of action studies are discussed.

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