Evolved Glyphosate Resistance in Plants: Biochemical and Genetic Basis of Resistance

Resistance to the herbicide glyphosate is currently known in at least eight weed species from many countries. Some populations of goosegrass from Malaysia, rigid ryegrass from Australia, and Italian ryegrass from Chile exhibit target site–based resistance to glyphosate through changes at amino acid 106 of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. Mutations change amino acid 106 from proline to either serine or threonine, conferring an EPSPS weakly resistant to glyphosate. The moderate level of resistance is sufficient for commercial failure of the herbicide to control these plants in the field. Conversely, a nontarget site resistance mechanism has been documented in glyphosate-resistant populations of horseweed and rigid ryegrass from the United States and Australia, respectively. In these resistant plants, there is reduced translocation of glyphosate to meristematic tissues. Both of these mechanisms are inherited as a single, nuclear gene trait. Although at present only two glyphosate-resistance mechanisms are known, it is likely that other mechanisms will become evident. The already very large and still increasing reliance on glyphosate in many parts of the world will inevitably result in more glyphosate-resistant weeds, placing the sustainability of this precious herbicide resource at risk.

Download Full-text

A Decade of Glyphosate-ResistantLoliumaround the World: Mechanisms, Genes, Fitness, and Agronomic Management

Weed Science ◽

10.1614/ws-08-181.1 ◽

2009 ◽

Vol 57 (4) ◽

pp. 435-441 ◽

Cited By ~ 102

Author(s):

Christopher Preston ◽

Angela M. Wakelin ◽

Fleur C. Dolman ◽

Yazid Bostamam ◽

Peter Boutsalis

Keyword(s):

Weed Management ◽

Single Gene ◽

Glyphosate Resistance ◽

Resistance Mechanisms ◽

Target Site ◽

Italian Ryegrass ◽

Shoot Meristem ◽

Agronomic Management ◽

Translocation Mechanism ◽

Rigid Ryegrass

Glyphosate resistance was first discovered in populations of rigid ryegrass in Australia in 1996. Since then, glyphosate resistance has been detected in additional populations of rigid ryegrass and Italian ryegrass in several other countries. Glyphosate-resistant rigid ryegrass and Italian ryegrass have been selected in situations where there is an overreliance on glyphosate to the exclusion of other weed control tactics. Two major mechanisms of glyphosate resistance have been discovered in these two species: a change in the pattern of glyphosate translocation such that glyphosate accumulates in the leaf tips of resistant plants instead of in the shoot meristem; and amino acid substitutions at Pro 106 within the target site, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). There are also populations with both mechanisms. In the case of glyphosate resistance, the target site mutations tend to provide a lower level of resistance than does the altered translocation mechanism. Each of these resistance mechanisms is inherited as a single gene trait that is largely dominant. As these ryegrass species are obligate outcrossers, this ensures resistance alleles can move in both pollen and seed. Some glyphosate-resistant rigid ryegrass populations appear to have a significant fitness penalty associated with the resistance allele. Field surveys show that strategies vary in their ability to reduce the frequency of glyphosate resistance in populations and weed population size, with integrated strategies—including alternative weed management and controlling seed set of surviving plants—the most effective.

Download Full-text

Transcriptome Analysis Identifies Candidate Target Genes Involved in Glyphosate-Resistance Mechanism in Lolium multiflorum

Plants ◽

10.3390/plants9060685 ◽

2020 ◽

Vol 9 (6) ◽

pp. 685

Author(s):

Joanei Cechin ◽

Cristiano Piasecki ◽

Daiane P. Benemann ◽

Frederico S. Kremer ◽

Vanessa Galli ◽

...

Keyword(s):

Target Genes ◽

De Novo ◽

Average Length ◽

Lolium Multiflorum ◽

Significant Proportion ◽

Resistance Mechanism ◽

Glyphosate Resistance ◽

Italian Ryegrass ◽

Weed Species ◽

Candidate Target

Italian ryegrass (Lolium multiflorum; LOLMU) is one of the most troublesome weeds in temperate regions in the world. This weed species interfere with wheat, corn, rye, and oat, causing significant crop yield losses. This species has evolved glyphosate resistance, making it difficult to control. The mechanisms of glyphosate resistance are still unknown, and an understanding thereof will favor the development of new strategies of management. The present study is the first transcriptome study in LOLMU using glyphosate-resistant and -sensitive biotypes, aiming to identify and to provide a list of the candidate target genes related to glyphosate resistance mechanism. The transcriptome was assembled de novo, producing 87,433 contigs with an N50 of 740 bp and an average length of 575 bp. There were 92 and 54 up- and down-regulated genes, respectively, in the resistant biotype, while a total of 1683 were differentially expressed in the sensitive biotype in response to glyphosate treatment. We selected 14 highly induced genes and seven with repressed expression in the resistant biotype in response to glyphosate. Of these genes, a significant proportion were related to the plasma membrane, indicating that there is a barrier making it difficult for glyphosate to enter the cell.

Download Full-text

A Modified phosphate-carrier protein theory is proposed as a non-target site mechanism For glyphosate resistance in weeds

Planta Daninha ◽

10.1590/s0100-83582010000500025 ◽

2010 ◽

Vol 28 (spe) ◽

pp. 1175-1185 ◽

Cited By ~ 11

Author(s):

A.C. Roso ◽

R.A. Vidal

Keyword(s):

Control Measure ◽

Shikimate Pathway ◽

Aromatic Amino Acids ◽

Glyphosate Resistance ◽

Resistance Mechanisms ◽

Target Site ◽

Weed Species ◽

Resistance Level ◽

Epsps Gene ◽

Limited Degree

Glyphosate is an herbicide that inhibits the enzyme 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPs) (EC 2.5.1.19). EPSPs is the sixth enzyme of the shikimate pathway, by which plants synthesize the aromatic amino acids phenylalanine, tyrosine, and tryptophan and many compounds used in secondary metabolism pathways. About fifteen years ago it was hypothesized that it was unlikely weeds would evolve resistance to this herbicide because of the limited degree of glyphosate metabolism observed in plants, the low resistance level attained to EPSPs gene overexpression, and because of the lower fitness in plants with an altered EPSPs enzyme. However, today 20 weed species have been described with glyphosate resistant biotypes that are found in all five continents of the world and exploit several different resistant mechanisms. The survival and adaptation of these glyphosate resistant weeds are related toresistance mechanisms that occur in plants selected through the intense selection pressure from repeated and exclusive use of glyphosate as the only control measure. In this paper the physiological, biochemical, and genetic basis of glyphosate resistance mechanisms in weed species are reviewed and a novel and innovative theory that integrates all the mechanisms of non-target site glyphosate resistance in plants is presented.

Download Full-text

Frost Reduces Clethodim Efficacy in Clethodim-Resistant Rigid Ryegrass (Lolium rigidum) Populations

Weed Science ◽

10.1614/ws-d-15-00140.1 ◽

2016 ◽

Vol 64 (2) ◽

pp. 207-215 ◽

Cited By ~ 1

Author(s):

Rupinder Kaur Saini ◽

Jenna Malone ◽

Christopher Preston ◽

Gurjeet S. Gill

Keyword(s):

Dose Response ◽

Coenzyme A ◽

Resistance Mechanism ◽

Lolium Rigidum ◽

Weed Species ◽

Susceptible Population ◽

Acetyl Coenzyme A ◽

Survival Percentage ◽

Rigid Ryegrass ◽

Acetyl Coenzyme A Carboxylase

Rigid ryegrass, an important annual weed species in cropping regions of southern Australia, has evolved resistance to 11 major groups of herbicides. Dose–response studies were conducted to determine response of three clethodim-resistant populations and one clethodim-susceptible population of rigid ryegrass to three different frost treatments (−2 C). Clethodim-resistant and -susceptible plants were exposed to frost in a frost chamber from 4:00 P.M. to 8:00 A.M. for three nights before or after clethodim application and were compared with plants not exposed to frost. A reduction in the level of clethodim efficacy was observed in resistant populations when plants were exposed to frost for three nights before or after clethodim application. In the highly resistant populations, the survival percentage and LD50were higher when plants were exposed to frost before clethodim application compared with frost after clethodim application. However, frost treatment did not influence clethodim efficacy of the susceptible population. Sequencing of the acetyl coenzyme A carboxylase (ACCase) gene of the three resistant populations identified three known mutations at positions 1781, 2041, and 2078. However, most individuals in the highly resistant populations did not contain any known mutation in ACCase, suggesting the resistance mechanism was a nontarget site. The effect of frost on clethodim efficacy in resistant plants may be an outcome of the interaction between frost and the clethodim resistance mechanism(s) present.

Download Full-text

Transfer of resistance alleles from herbicide-resistant to susceptible grass weeds via pollen-mediated gene flow

Weed Technology ◽

10.1017/wet.2021.82 ◽

2021 ◽

pp. 1-51

Author(s):

Amit J. Jhala ◽

Hugh J. Beckie ◽

Carol Mallory-Smith ◽

Marie Jasieniuk ◽

Roberto Busi ◽

...

Keyword(s):

Gene Flow ◽

Herbicide Resistance ◽

Creeping Bentgrass ◽

Agricultural Landscapes ◽

Italian Ryegrass ◽

Weed Species ◽

Herbicide Resistant ◽

Wild Oats ◽

Rigid Ryegrass ◽

Grass Weed

Abstract The objective of this paper was to review the reproductive biology, herbicide-resistant (HR) biotypes, pollen-mediated gene flow (PMGF), and potential for transfer of alleles from HR to susceptible grass weeds including barnyardgrass, creeping bentgrass, Italian ryegrass, johnsongrass, rigid (annual) ryegrass, and wild oats. The widespread occurrence of HR grass weeds is at least partly due to PMGF, particularly in obligate outcrossing species such as rigid ryegrass. Creeping bentgrass, a wind-pollinated turfgrass species, can efficiently disseminate herbicide resistance alleles via PMGF and movement of seeds and stolons. The genus Agrostis contains about 200 species, many of which are sexually compatible and produce naturally occurring hybrids as well as producing hybrids with species in the genus Polypogon. The self-incompatibility, extremely high outcrossing rate, and wind pollination in Italian ryegrass clearly point to PMGF as a major mechanism by which herbicide resistance alleles can spread across agricultural landscapes, resulting in abundant genetic variation within populations and low genetic differentiation among populations. Italian ryegrass can readily hybridize with perennial ryegrass and rigid ryegrass due to their similarity in chromosome numbers (2n=14), resulting in interspecific gene exchange. Johnsongrass, barnyardgrass, and wild oats are self-pollinated species, so the potential for PMGF is relatively low and limited to short distances; however, seeds can easily shatter upon maturity before crop harvest, leading to wider dispersal. The occurrence of PMGF in reviewed grass weed species, even at a low rate is greater than that of spontaneous mutations conferring herbicide resistance in weeds and thus can contribute to the spread of herbicide resistance alleles. This review indicates that the transfer of herbicide resistance alleles occurs under field conditions at varying levels depending on the grass weed species.

Download Full-text

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

Weed Technology ◽

10.1017/wet.2020.74 ◽

2020 ◽

pp. 1-12 ◽

Cited By ~ 1

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.

Download Full-text

Antimicrobial Susceptibility and Clonality of Clinical Ureaplasma Isolates in the United States

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00671-16 ◽

2016 ◽

Vol 60 (8) ◽

pp. 4793-4798 ◽

Cited By ~ 18

Author(s):

Javier Fernández ◽

Melissa J. Karau ◽

Scott A. Cunningham ◽

Kerryl E. Greenwood-Quaintance ◽

Robin Patel

Keyword(s):

United States ◽

Antimicrobial Susceptibility ◽

Antimicrobial Agents ◽

Ureaplasma Urealyticum ◽

Resistance Mechanism ◽

The United States ◽

Resistance Mechanisms ◽

Resistant Isolate ◽

Limited Information ◽

Content Type

ABSTRACTUreaplasma urealyticumandUreaplasma parvumare pathogens involved in urogenital tract and intrauterine infections and also in systemic diseases in newborns and immunosuppressed patients. There is limited information on the antimicrobial susceptibility and clonality of these species. In this study, we report the susceptibility of 250 contemporary isolates ofUreaplasma(202U. parvumand 48U. urealyticumisolates) recovered at Mayo Clinic, Rochester, MN. MICs of doxycycline, azithromycin, ciprofloxacin, tetracycline, erythromycin, and levofloxacin were determined by broth microdilution, with MICS of the last three interpreted according to CLSI guidelines. Levofloxacin resistance was found in 6.4% and 5.2% ofU. parvumandU. urealyticumisolates, respectively, while 27.2% and 68.8% of isolates, respectively, showed ciprofloxacin MICs of ≥4 μg/ml. The resistance mechanism of levofloxacin-resistant isolates was due to mutations inparC, with the Ser83Leu substitution being most frequent, followed by Glu87Lys. No macrolide resistance was found among the 250 isolates studied; a singleU. parvumisolate was tetracycline resistant.tet(M) was found in 10U. parvumisolates, including the single tetracycline-resistant isolate, as well as in 9 isolates which had low tetracycline and doxycycline MICs. Multilocus sequence typing (MLST) performed on a selection of 46 isolates showed high diversity within the clinicalUreaplasmaisolates studied, regardless of antimicrobial susceptibility. The present work extends previous knowledge regarding susceptibility to antimicrobial agents, resistance mechanisms, and clonality ofUreaplasmaspecies in the United States.

Download Full-text

Differentiation of Life-History Traits among Palmer Amaranth Populations (Amaranthus palmeri) and Its Relation to Cropping Systems and Glyphosate Sensitivity

Weed Science ◽

10.1017/wsc.2017.14 ◽

2017 ◽

Vol 65 (3) ◽

pp. 339-349 ◽

Cited By ~ 19

Author(s):

Washington Bravo ◽

Ramon G. Leon ◽

Jason A. Ferrell ◽

Michael J. Mulvaney ◽

C. Wesley Wood

Keyword(s):

Life History ◽

Crop Rotation ◽

Life History Traits ◽

Cropping Systems ◽

Glyphosate Resistance ◽

The United States ◽

Organic Production ◽

Palmer Amaranth ◽

Flowering Plant ◽

Weed Species

Palmer amaranth’s ability to evolve resistance to different herbicides has been studied extensively, but there is little information about how this weed species might be evolving other life-history traits that could potentially make it more aggressive and difficult to control. We characterized growth and morphological variation among 10 Palmer amaranth populations collected in Florida and Georgia from fields with different cropping histories, ranging from continuous short-statured crops (vegetables and peanut) to tall crops (corn and cotton) and from intensive herbicide use history to organic production. Palmer amaranth populations differed in multiple traits such as fresh and dry weight, days to flowering, plant height, and leaf and canopy shape. Differences between populations for these traits ranged from 36% up to 87%. Although glyphosate-resistant (GR) populations collected from cropping systems including GR crops exhibited higher values of the aforementioned variables than glyphosate-susceptible (GS) populations, variation in traits was not explained by glyphosate resistance or distance between populations. Cropping system components such as crop rotation and crop canopy structure better explained the differences among populations. The higher growth of GR populations compared with GS populations was likely the result of multiple selection forces present in the cropping systems in which they grow rather than a pleiotropic effect of the glyphosate resistance trait. Results suggest that Palmer amaranth can evolve life-history traits increasing its growth and reproduction potential in cropping systems, which explains its rapid spread throughout the United States. Furthermore, our findings highlight the need to consider the evolutionary consequences of crop rotation structure and the use of more competitive crops, which might promote the selection of more aggressive biotypes in weed species with high genetic variability.

Download Full-text

The Triple Amino Acid Substitution TAP-IVS in the EPSPS Gene Confers High Glyphosate Resistance to the Superweed Amaranthus hybridus

International Journal of Molecular Sciences ◽

10.3390/ijms20102396 ◽

2019 ◽

Vol 20 (10) ◽

pp. 2396 ◽

Cited By ~ 15

Author(s):

Maria J. García ◽

Candelario Palma-Bautista ◽

Antonia M. Rojano-Delgado ◽

Enzo Bracamonte ◽

João Portugal ◽

...

Keyword(s):

Amino Acid ◽

Amino Acid Substitution ◽

Glyphosate Resistance ◽

Wild Type ◽

Triple Mutant ◽

Resistance Level ◽

Amaranthus Hybridus ◽

Susceptible Population ◽

Epsps Gene ◽

Wide Range

The introduction of glyphosate-resistant (GR) crops revolutionized weed management; however, the improper use of this technology has selected for a wide range of weeds resistant to glyphosate, referred to as superweeds. We characterized the high glyphosate resistance level of an Amaranthus hybridus population (GRH)—a superweed collected in a GR-soybean field from Cordoba, Argentina—as well as the resistance mechanisms that govern it in comparison to a susceptible population (GSH). The GRH population was 100.6 times more resistant than the GSH population. Reduced absorption and metabolism of glyphosate, as well as gene duplication of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) or its overexpression did not contribute to this resistance. However, GSH plants translocated at least 10% more 14C-glyphosate to the rest of the plant and roots than GRH plants at 9 h after treatment. In addition, a novel triple amino acid substitution from TAP (wild type, GSH) to IVS (triple mutant, GRH) was identified in the EPSPS gene of the GRH. The nucleotide substitutions consisted of ATA102, GTC103 and TCA106 instead of ACA102, GCG103, and CCA106, respectively. The hydrogen bond distances between Gly-101 and Arg-105 positions increased from 2.89 Å (wild type) to 2.93 Å (triple-mutant) according to the EPSPS structural modeling. These results support that the high level of glyphosate resistance of the GRH A. hybridus population was mainly governed by the triple mutation TAP-IVS found of the EPSPS target site, but the impaired translocation of herbicide also contributed in this resistance.

Download Full-text

Two New Mechanisms of Macrolide Resistance in Clinical Strains ofStreptococcus pneumoniae from Eastern Europe and North America

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.44.12.3395-3401.2000 ◽

2000 ◽

Vol 44 (12) ◽

pp. 3395-3401 ◽

Cited By ~ 184

Author(s):

A. Tait-Kamradt ◽

T. Davies ◽

P. C. Appelbaum ◽

F. Depardieu ◽

P. Courvalin ◽

...

Keyword(s):

Amino Acid ◽

North America ◽

Eastern Europe ◽

Ribosomal Proteins ◽

Fold Increase ◽

The United States ◽

Resistance Mechanisms ◽

Macrolide Resistance ◽

23S Rrna ◽

Isogenic Strains

ABSTRACT Resistance to macrolides in pneumococci is generally mediated by methylation of 23S rRNA via erm(B) methylase which can confer a macrolide (M)-, lincosamide (L)-, and streptogramin B (SB)-resistant (MLSB) phenotype or by drug efflux via mef(A) which confers resistance to 14- and 15-membered macrolides only. We studied 20 strains with unusual ML or MSB phenotypes which did not harbor erm(B) ormef(A). The strains had been isolated from patients in Eastern Europe and North America from 1992 to 1998. These isolates were found to contain mutations in genes for either 23S rRNA or ribosomal proteins. Three strains from the United States with an ML phenotype, each representing a different clone, were characterized as having an A2059G (Escherichia coli numbering) change in three of the four 23S rRNA alleles. Susceptibility to macrolides and lincosamides decreased as the number of alleles in isogenic strains containing A2059G increased. Sixteen MSB strains from Eastern Europe were found to contain a 3-amino-acid substitution (69GTG71 to TPS) in a highly conserved region of the ribosomal protein L4 (63KPWRQKGTGRAR74). These strains formed several distinct clonal types. The single MSB strain from Canada contained a 6-amino-acid L4 insertion (69GTGREKGTGRAR), which impacted growth rate and also conferred a 500-fold increase in MIC on the ketolide telithromycin. These macrolide resistance mechanisms from clinical isolates are similar to those recently described for laboratory-derived mutants.

Download Full-text