Glyphosate-resistant Crops Research Articles

Evaluation of Postemergence Weed Control Programs in Cotton Without the Addition of Glyphosate

Glyphosate has played an important role in agricultural production systems, especially after the release of glyphosate resistant crops. With increased usage and an overall reliance on chemical control, weed resistance to glyphosate has occurred and is now a major issue. The objective of this research was to investigate weed control levels provided by glufosinate, 2,4-D, and clethodim as an alternative to glyphosate. Multiple POST applications generally provided superior weed control in comparison to a single early-POST application. No programs provided greater than 80% warm-season grass control beginning 21 d after mid-POST application. Applications of glufosinate or glufosinate + 2,4-D fb clethodim + glufosinate, glufosinate + 2,4-D, or clethodim + glufosinate + 2,4-D provided adequate broadleaf weed control throughout the rating period. Although POST-only programs are an option, they are not a sustainable weed control practice. It remains important to incorporate residual herbicides into a weed control program as well as alternative weed control methods.

Development of a double-antibody sandwich ELISA for quantification of mutated EPSPS gene expression in rice

Glyphosate resistance is a critically important trait for genetically modified (GM) crops. Mutation of the rice EPSPS gene results in a high level of glyphosate resistance, presenting significant potential for the development of glyphosate-tolerant crops. The resistance of rice to glyphosate is correlated with the expression levels of resistance genes. Therefore, developing a convenient, stable, and sensitive method for quantifying the OsmEPSPS protein is crucial for the development of glyphosate-resistant crops. We developed a double-antibody sandwich quantitative ELISA (DAS-ELISA) using a specific monoclonal antibody (mAb) for OsmEPSPS capture and an HRP-conjugated anti-OsmEPSPS rabbit polyclonal antibody (pAb). The method could be used to detect OsmEPSPS within a linear range of 16–256 ng/mL with robust intra- and inter-batch duplicability (%CV values: 0.17 %–7.24 %). OsmEPSPS expression in the transgenic rice lines (54.44–445.80 μg/g) was quantified using the DAS-ELISA. Furthermore, the expression of the OsmEPSPS gene was validated through Western blotting. This study demonstrated the reliability and stability of the DAS-ELISA for OsmEPSPS detection in GM rice.

Guardians of Liver Health: Unveiling the Resilient Shield of Antioxidant Vitamins (C, E) Against Glyphosate-Induced Havoc in Experimental Rats

Glyphosate, a widely used herbicide, has gained popularity due to its broad-spectrum effects and use in genetically modified, glyphosate-resistant crops. Recent data, however, points to possible adverse effects of glyphosate and herbicides based on glyphosate, such as genotoxic and cytotoxic effects, elevated stress levels, disturbance of the hormones such as estrogen pathway and possible associations with specific cancer types. This has raised concerns about the widespread use of glyphosate and its impact on human health and the environment. The objective of this study was to determine whether antioxidants vitamin C and E could shield experimental rats' livers from the damaging effects of glyphosate. Animals were grouped as Group I-control, 30 days of oral glyphosate-treated rats as Group II, and Rats that received simultaneous glyphosate treatment and oral administration of vitamins C and E were for 30 days as Group III. We used the user's manual to figure out the fasting blood glucose (FBG) levels, the histomorphology of liver tissue using H&E staining, and the liver and kidney function tests using Diatek Greiner kits. The study revealed that prolonged exposure to glyphosate can alter the SREBPI and HNF1 pathways, leading to diabetes. As an herbicide, glyphosate can cause harmful changes in vital organs, leading to diabetes and other disorders.

Unraveling the atomic mechanisms underlying glyphosate insensitivity in EPSPS: implications of distal mutations

5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS), as an indispensable enzyme in the shikimate pathway, is the specific target of grasser killer glyphosate (GPJ). GPJ is a competitive inhibitor of phosphoenolpyruvate (PEP), which is the natural substrate of EPSPS. A novel Ls-EPSPS gene variant discovered from Liliaceae, named ELs-EPSPS, includes five distal mutations, E112V, D142N, T351S, D425G, and R496G, endowing high GPJ insensitivity. However, the implicit molecular mechanism of the enhanced tolerance/insensitivity of GPJ in ELs-EPSPS is not fully understood. Herein, we try to interpret the hidden molecular mechanism using computational methods. Computational results reveal the enhanced flexibility of apo EPSPS upon mutations. The enhanced affinity of the initial binding substrate shikimate-3-phosphate (S3P), and the higher probability of second ligands PEP/GPJ entering the pocket are observed in the ELs-EPSPS-S3P system. Docking and MD results further confirmed the decreased GPJ-induced EPSPS inhibition upon mutations. And, the alterations of K98 and R179 side-chain orientations upon mutations are detrimental to GPJ binding at the active site. Additionally, the oscillation of side chain K98, in charge of PEP location, improves the proximity effect for substrates in the dual-substrate systems upon mutations. Our results clarify that the enhanced GPJ tolerance of EPSPS is achieved from decreased competitive inhibition of GPJ at the atomic perspective, and this finding further contributes to the cultivation of EPSPS genes with higher GPJ tolerance/insensitivity and a mighty renovation for developing glyphosate-resistant crops. Communicated by Ramaswamy H. Sarma

Oxidative Stress and Cytotoxicity Induced by Co-Formulants of Glyphosate-Based Herbicides in Human Mononuclear White Blood Cells.

The use of genetically modified, glyphosate-resistant crops has led to the widespread application of glyphosate-based herbicides (GBHs), making them one of the most widely used herbicide formulations on the market. To enhance the efficacy of the active ingredient, GBHs used in practice often contain other ingredients marked as inert "adjuvants" or "co-formulants", the toxic properties of which are poorly understood. The objective of this study was to compare the cytotoxic effects of pure glyphosate, three GBHs (Roundup Mega, Fozat 480 and Glyfos) and two co-formulants commonly used in GBHs as assessed via CCK-8 assay, and the extent of their potential oxidative damage as assessed via superoxide dismutase (SOD) assay, in order to reveal the role of adjuvants in the toxicity of the formulations. Our results showed that glyphosate alone did not significantly affect cell viability. In contrast, GBHs and adjuvants induced a pronounced cytotoxic effect from a concentration of 100 μM. SOD activity of cells treated with GBHs or adjuvants was significantly lower compared to cells treated with glyphosate alone. This suggests that the adjuvants in GBHs are responsible for the cytotoxic effects of the formulations through the induction of oxidative stress.

The silver bullet that wasn't: Rapid agronomic weed adaptations to glyphosate in North America.

The rapid adoption of glyphosate-resistant crops at the end of the 20th century caused a simplification of weed management that relied heavily on glyphosate for weed control. However, the effectiveness of glyphosate has diminished. A greater understanding of trends related to glyphosate use will shed new light on weed adaptation to a product that transformed global agriculture. Objectives were to (1) quantify the change in weed control efficacy from postemergence (POST) glyphosate use on troublesome weeds in corn and soybean and (2) determine the extent to which glyphosate preceded by a preemergence (PRE) improved the efficacy and consistency of weed control compared to glyphosate alone. Herbicide evaluation trials from 24 institutions across the United States of America and Canada from 1996 to 2021 were compiled into a single database. Two subsets were created; one with glyphosate applied POST, and the other with a PRE herbicide followed by glyphosate applied POST. Within each subset, mean and variance of control ratings for seven problem weed species were regressed over time for nine US states and one Canadian province. Mean control with POST glyphosate alone decreased over time while variability in control increased. Glyphosate preceded by a labeled PRE herbicide showed little change in mean control or variability in control over time. These results illustrate the rapid adaptation of agronomically important weed species to the paradigm-shifting product glyphosate. Including more diversity in weed management systems is essential to slowing weed adaptation and prolonging the usefulness of existing and future technologies.

Glyphosate decreases survival, increases fecundity, and alters the microbiome of the natural predator Harmonia axyridis (ladybird beetle)

Glyphosate is a widely-used herbicide that shows toxicity to non-target organisms. The predatory natural enemy Harmonia axyridis may ingest glyphosate present in pollen and aphid prey. The present study characterized the responses of adult H. axyridis to environmentally relevant concentrations of glyphosate (5, 10, and 20 mg/L) for one or five days. There were no obvious effects on adult H. axyridis survival rates or fecundity in response to 5 or 10 mg/L glyphosate. However, exposure to 20 mg/L glyphosate significantly reduced the survival rate and increased fecundity. Analysis of the adult H. axyridis microbiota with 16S rRNA sequencing demonstrated changes in the relative and/or total abundance of specific taxa, including Serratia, Enterobacter, Staphylococcus, and Hafnia-Obesumbacterium. These changes in symbiotic bacterial abundance may have led to changes in survival rates or fecundity of this beetle. This is the first report of herbicide-induced stimulation of fecundity in a non-target predatory natural enemy, reflecting potentially unexpected risks of glyphosate exposure in adult H. axyridis. Although glyphosate resistant crops have been widely planted, the results of this study indicate a need to strengthen glyphosate management to prevent over-use, which could cause glyphosate toxicity and threaten environmental and human health.

In maize, co-expression of GAT and GR79-EPSPS provides high glyphosate resistance, along with low glyphosate residues

Herbicide tolerance has been the dominant trait introduced during the global commercialization of genetically modified (GM) crops. Herbicide-tolerant crops, especially glyphosate-resistant crops, offer great advantages for weed management; however, despite these benefits, glyphosate-resistant maize (Zea mays L.) has not yet been commercially deployed in China. To develop a new bio-breeding resource for glyphosate-resistant maize, we introduced a codon-optimized glyphosate N-acetyltransferase gene, gat, and the enolpyruvyl-shikimate-3-phosphate synthase gene, gr79-epsps, into the maize variety B104. We selected a genetically stable high glyphosate resistance (GR) transgenic event, designated GG2, from the transgenic maize population through screening with high doses of glyphosate. A molecular analysis demonstrated that single copy of gat and gr79-epsps were integrated into the maize genome, and these two genes were stably transcribed and translated. Field trials showed that the transgenic event GG2 could tolerate 9000 g acid equivalent (a.e.) glyphosate per ha with no effect on phenotype or yield. A gas chromatography-mass spectrometry (GC–MS) analysis revealed that, shortly after glyphosate application, the glyphosate (PMG) and aminomethylphosphonic acid (AMPA) residues in GG2 leaves decreased by more than 90% compared to their levels in HGK60 transgenic plants, which only harbored the epsps gene. Additionally, PMG and its metabolic residues (AMPA and N-acetyl-PMG) were not detected in the silage or seeds of GG2, even when far more than the recommended agricultural dose of glyphosate was applied. The co-expression of gat and gr79-epsps, therefore, confers GG2 with high GR and a low risk of herbicide residue accumulation, making this germplasm a valuable GR event in herbicide-tolerant maize breeding.

Gastrointestinal Microbial Ecology of Weaned Piglets Fed Diets with Different Levels of Glyphosate.

Glyphosate possesses antimicrobial properties, and the present study investigated potential effects of feed glyphosate on piglet gastrointestinal microbial ecology. Weaned piglets were allocated to four diets (glyphosate contents [mg/kg feed]: 0 mg/kg control [CON; i.e., basal diet with no glyphosate added], 20 mg/kg as Glyphomax commercial herbicide [GM20], and 20 mg/kg [IPA20] and 200 mg/kg [IPA200] as glyphosate isopropylamine [IPA] salt). Piglets were sacrificed after 9 and 35 days of treatment, and stomach, small intestine, cecum, and colon digesta were analyzed for glyphosate, aminomethylphosphonic acid (AMPA), organic acids, pH, dry matter content, and microbiota composition. Digesta glyphosate contents reflected dietary levels (on day 35, 0.17, 16.2, 20.5, and 207.5 mg/kg colon digesta, respectively). Overall, we observed no significant glyphosate-associated effects on digesta pH, dry matter content, and-with few exceptions-organic acid levels. On day 9, only minor gut microbiota changes were observed. On day 35, we observed a significant glyphosate-associated decrease in species richness (CON, 462; IPA200, 417) and in the relative abundance of certain Bacteroidetes genera: CF231 (CON, 3.71%; IPA20, 2.33%; IPA200, 2.07%) and g_0.24 (CON, 3.69%; IPA20, 2.07%; IPA200, 1.75%) in cecum. No significant changes were observed at the phylum level. In the colon, we observed a significant glyphosate-associated increase in the relative abundance of Firmicutes (CON, 57.7%; IPA20, 69.4%; IPA200, 66.1%) and a decrease in Bacteroidetes (CON, 32.6%; IPA20, 23.5%). Significant changes were only observed for few genera, e.g., g_0.24 (CON, 7.12%; IPA20, 4.59%; IPA200, 4.00%). In conclusion, exposing weaned piglets to glyphosate-amended feed did not affect gastrointestinal microbial ecology to a degree that was considered actual dysbiosis, e.g., no potential pathogen bloom was observed. IMPORTANCE Glyphosate residues can be found in feed made from genetically modified glyphosate-resistant crops treated with glyphosate or from conventional crops, desiccated with glyphosate before harvest. If these residues affect the gut microbiota to an extent that is unfavorable to livestock health and productivity, the widespread use of glyphosate on feed crops may need to be reconsidered. Few in vivo studies have been conducted to investigate potential impact of glyphosate on the gut microbial ecology and derived health issues of animals, in particular livestock, when exposed to dietary glyphosate residues. The aim of the present study was therefore to investigate potential effects on the gastrointestinal microbial ecology of newly weaned piglets fed glyphosate-amended diets. Piglets did not develop actual gut dysbiosis when fed diets, containing a commercial herbicide formulation or a glyphosate salt at the maximum residue level, defined by the European Union for common feed crops, or at a 10-fold-higher level.

Comparison of Glyphosate-Degradation Ability of Aldo-Keto Reductase (AKR4) Proteins in Maize, Soybean and Rice.

Genes that participate in the degradation or isolation of glyphosate in plants are promising, for they endow crops with herbicide tolerance with a low glyphosate residue. Recently, the aldo-keto reductase (AKR4) gene in Echinochloa colona (EcAKR4) was identified as a naturally evolved glyphosate-metabolism enzyme. Here, we compared the glyphosate-degradation ability of theAKR4 proteins from maize, soybean and rice, which belong to a clade containing EcAKR4 in the phylogenetic tree, by incubation of glyphosate with AKR proteins both in vivo and in vitro. The results indicated that, except for OsALR1, the other proteins were characterized as glyphosate-metabolism enzymes, with ZmAKR4 ranked the highest activity, and OsAKR4-1 and OsAKR4-2 exhibiting the highest activity among the AKR4 family in rice. Moreover, OsAKR4-1 was confirmed to endow glyphosate-tolerance at the plant level. Our study provides information on the mechanism underlying the glyphosate-degradation ability of AKR proteins in crops, which enables the development of glyphosate-resistant crops with a low glyphosate residue, mediated by AKRs.

Impact of glyphosate residues in sow diets on neonatal piglets: tail kinks, stillborn and diarrhoea

Among the applications, glyphosate-based herbicides are used for pre-harvest crop desiccation and weed management in glyphosate resistant crops. Due to these applications glyphosate residues have been found in feedstuff for conventional livestock. Besides its herbicidal property, glyphosate has documented mineral chelating and antimicrobial properties. Previous studies have found glyphosate residuals in animal organs, and glyphosate may cause adverse effects in animals during the embryonic or neonatal period. The present study has two endpoints; (1) whether glyphosate concentration in the diets fed to sows during early gestation, was associated with the frequency of congenital tail kinks and stillborn piglets, and (2) whether the glyphosate concentration in diets fed to lactating sows, is associated with the frequency of diarrhoea in neonatal piglets. The concentration of glyphosate in 78 gestation diets obtained from seven Danish conventional sow herds ranged from 0.08 to 1.52 mg/kg dry matter (DM) and in 34 lactation diets from 0.06 to 0.87 mg/kg DM. When correcting for an average DM content of 88.3% in gestation diets and 89.0% in lactation diets the concentration of glyphosate ranged from 0.07 to 1.34 and 0.05 to 0.77 mg/kg feed, respectively. In the first study, 28,336 docked tails from 2 to 4-day-old piglets were assessed for congenital tail kinks and the number of kinky tails per herd per week was linked to the glyphosate concentration in sow diets during week 1 to 6 of gestation. Percentage of kinky tails and stillborn piglets ranged from 0 to 2.60% and 0.7 to 3.2% per week, respectively. No associations between the glyphosate concentration in sow gestation diets and the frequency of kinky tails or stillborn piglets were found. In the second study, faeces consistency of 5,526 piglets from 386 litters was linked to the glyphosate concentration in sow lactation diets. A proportion of 0.15 of the 0- to 5-day-old piglets had diarrhoea. No association was found between the concentration of glyphosate in sow lactation diets and the frequency of diarrhoea in neonatal piglets.

Functional characterization of glycine oxidase from Bacillus licheniformis in Escherichia coli and transgenic plants.

To find glycine oxidase genes that can be applied to the breeding of glyphosate resistant crops. The glycine oxidase (GO, EC 1.4.3.19) gene (GenBank No: KC831746) from Bacillus licheniformis (B. licheniformis) was chemically synthesized and transformed into glyphosate-sensitive Escherichia coli (E. coli). The GO gene was transformed into Arabidopsis and rice through Agrobacterium-mediated transformation. The test results confirmed that transgenic plants containing GO genes are more resistant to glyphosate than wild-type plants. On solid Murashige and Skoog (MS) (Murashige and Skoog1962 ) medium containing 200µM glyphosate, transgenic Arabidopsis thaliana grew normally, while wild-type plants were stunted and root growth was restricted. In a solution containing 500µM glyphosate, wild-type rice showed severe yellowing, while transgenic rice grew normally. In addition, when sprayed with 10mM glyphosate solution, wild-type rice withered and died, while transgenic rice grew well. The function of GO gene in glyphosate resistance and the application value of GO gene in the cultivation of glyphosate-resistant crops is proved. The glycine oxidase gene from B. licheniformis enhances the resistance of E. coli, Arabidopsis and rice to glyphosate.

Glyphosate affects the susceptibility of non-target native plant species according to their stage of development and degree of exposure in the landscape

Unsustainable agriculture is producing a great socio-ecological transformation in Latin America because it has expanded into areas occupied by native forests. Glyphosate is the most widely used herbicide, with severe ecotoxicological effects on non-target organisms. The aim of this study was to determine the effects of glyphosate on seedlings of 24 non-target herbaceous and non-herbaceous plant species present in forest relicts of Argentine Chaco. The effects of a gradient of glyphosate doses (525, 1050, 2100, 4200, and 8400 g ai/ha) were measured in seedlings of each species under greenhouse conditions. Seedlings were grown from seeds collected from native forest fragments of different sizes (assuming three different degrees of historical exposure to glyphosate in the landscape). Doses were applied at different stages of seedling development (five- and ten-weeks after emergence), and phytotoxicity, growth reduction, and sensitivity were measured. Glyphosate produced lethal or sublethal effects in all 24 species, some of which were very sensitive (>60 % of the species presented strong to severe growth reduction with ¼ of the dose used on crops). The greatest toxicological effects were related to early stage of development, herbaceous species, and low historical exposure to glyphosate. According to the species sensitivity distribution, the drift-dose to protect 95 % of the plant species that occur in larger forest fragments should not exceed 5 % of the dose commonly used on crops. These results suggest that the current weed management linked to glyphosate-resistant crops could lead to a gradual loss of biodiversity in the landscape. Concurrently, selection of glyphosate-tolerant biotypes in some non-target species could represent a very problematic cycle for the current model of industrial agriculture. Some alternatives for weed control are proposed.

Australia’s first case of glyphosate-resistant tall fleabane (Conyza sumatrensis) and alternative herbicide options for its control

AbstractTall fleabane is emerging as a problematic weed species in the eastern cropping region of Australia. Recently, growers indicated poor control of tall fleabane to the field rate of glyphosate in fallow fields. Pot studies were conducted in an open field at the Gatton farm of the University of Queensland, Queensland, Australia, to confirm the level of glyphosate resistance in a putative glyphosate-resistant (GR) tall fleabane population and to evaluate the performance of alternative postemergence herbicides to control GR tall fleabane. Compared with a glyphosate-susceptible (GS) population, the level of resistance in the GR population was 4-fold and 3.5-fold greater based on plant survival and biomass, respectively. The target-site resistance mechanism was not present because both the GR and GS populations had the same gene sequence. There were several effective alternative herbicides for the control of small (4-leaf stage) plants of tall fleabane, but to control large (12- to 14-leaf stage) plants, the sole application of saflufenacil + trifludimoxazin or its mixtures with glyphosate, glufosinate, or paraquat were the best herbicide treatments. This is the first published report on the occurrence of GR tall fleabane in Australia. Growers need to use integrated management strategies to mitigate the further spread of GR tall fleabane in fallow fields as well as glyphosate-resistant crops.

First report of glyphosate-resistant downy brome (Bromus tectorum L.) in Canada

Glyphosate is the most used herbicide worldwide, and is an important source of economical weed control in glyphosate-resistant crops, and conservation tillage systems, among other uses. Downy brome (Bromus tectorum L.), otherwise known as cheatgrass, is a highly invasive winter-annual grass weed in cropping systems, pastureland, and naturalized or ruderal areas in western North America. In 2021, a downy brome population remained uncontrolled following four applications of glyphosate in a glyphosate-resistant canola (Brassica napus L.) field located in Taber County, Alberta, Canada. All individuals from the subsequent generation of the population survived glyphosate treatment at the typical field rate (900 g ae ha−1). In dose-response bioassays, the putative glyphosate-resistant population exhibited 10.6- to 11.9-fold, 7.7- to 8.7-fold, 7.8- to 8.8-fold, and 8.3- to 9.5-fold resistance to glyphosate based on plant survival, visible control, and biomass fresh weight and dry weight, respectively, compared with two susceptible populations 21 days after treatment. Estimated glyphosate rates for 80% control of this population ranged from 2795 to 4511 g ae ha−1; well above common usage rates. This downy brome population represents the first glyphosate-resistant grass weed confirmed in Canada, and the second weed species exhibiting glyphosate resistance in the Canadian prairie region.

Stacking herbicide detoxification and resistant genes improves glyphosate tolerance and reduces phytotoxicity in tobacco (Nicotiana tabacum L.) and rice (Oryza sativa L.)

Glyphosate residues retained in the growing meristematic tissues or in grains of glyphosate-resistant crops affect the plants physiological functions and crop yield. Removing glyphosate residues in the plants is desirable with no penalty on crop yield and quality. We report a new combination of scientific strategy to detoxify glyphosate that reduces the residual levels and improve crop resistance. The glyphosate detoxifying enzymes Aldo-keto reductase (AKR1) and mutated glycine oxidase (mGO) with different modes of action were co-expressed with modified EPSPS, which is insensitive to glyphosate in tobacco (Nicotiana tabacum L.) and rice (Oryza sativa L.). The transgenic tobacco plants expressing individual PsAKR1, mGO, CP4-EPSPS, combinations of PsAKR1:CP4EPSPS, PsAKR1:mGO, and multigene with PsAKR1: mGO: CP4EPSPS genes were developed. The bio-efficacy studies of in-vitro leaf regeneration on different concentrations of glyphosate, seedling bioassay, and spray on transgenic tobacco plants demonstrate that glyphosate detoxification with enhanced resistance. Comparative analysis of the transgenic tobacco plants reveals that double and multigene expressing transgenics had reduced accumulation of shikimic acid, glyphosate, and its primary residue AMPA, and increased levels of sarcosine were observed in all PsAKR1 expressing transgenics. The multigene expressing rice transgenics showed improved glyphosate resistance with yield maintenance. In summary, results suggest that stacking genes with two different detoxification mechanisms and insensitive EPSPS is a potential approach for developing glyphosate-resistant plants with less residual content.

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GREENHOUSE GASES Reactions ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2022, 100 (28), p 4August 15, 2022Cite this:C&EN 100, 28, 4Letters to the editorClimate benefits of remote workIt seems that this is such a mundane topic, but during the pandemic, data showed that carbon dioxide levels were reduced significantly because there were fewer people on the road. As the pandemic expanded, the workplace continued to include those working at home. The Zoom tool showed itself as the model to work remotely. Eliminating high-rise office buildings and urban office environments appears to be relevant in the global business environment. It seems to me the logic shows that if people stay home and work from home, their CO2 footprint will be smaller. The CO2 reduction during the pandemic was so significant that it should be taken as a signal to change the way we do business.The American Chemical Society should encourage remote work space and reduced urban work spaces in favor of working at home. ACS policy should support enterprise stewardship in encouraging remote working to passively reduce CO2 emissions.Martha DibbleePortland, OregonACS members’ contributions to glyphosate researchGlyphosate has been the subject of one American Chemical Society Division of Agrochemicals (AGRO) symposium (2016), put together by Stephen O. Duke. Although the presentations were never published in an ACS Symposium Series, the participants contributed to a special issue of Pest Management Science published in 2018 ( DOI: 10.1002/ps.4902). As editor of ACS Symposium Series volume 1099 and member of the Editorial Board of Reviews of Environmental Contamination and Toxicology (RECT), I contacted Dr. Duke and requested he organize RECT volume 255 using presentations from the ACS AGRO symposium on glyphosate. The editor of RECT asked me to edit volume 255 on glyphosate. The volume includes four chapters: “Glyphosate Uses Other than in Glyphosate-Resistant Crops, Mode of Action, Degradation in Plants, and Effects on Non-target Plants and Agricultural Microbes,” “History and Outlook for Glyphosate-Resistant Crops,” “Evaluation of Glyphosate-Resistant Weeds,” and “Ecotoxicology of Glyphosate, Its Formulants, and Environmental Degradation Products.” Table i of the last chapter reviews key publications on the carcinogenicity of glyphosate.I believe RECT 255 should be mentioned in C&EN’s recent article on glyphosate (June 27, 2022, page 15), as it represents the work of ACS AGRO members and their contributions to herbicide chemistry.James B. KnaakFort Myers, Florida

Structural analysis and engineering of aldo-keto reductase from glyphosate-resistant Echinochloa colona

Glyphosate is a dominant organophosphate herbicide that inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) of the shikimate pathway. Glyphosate is extensively applied since manufactured, which has led to the emergence of various glyphosate-resistant crops and weeds. However, the molecular mechanism of many glyphosate-resistance machineries remains unclear. Recently, the upregulated expression of two homologous aldo-keto reductases (AKRs), designated as AKR4C16 and AKR4C17, were found to contribute to the glyphosate resistance in Echinochloa colona. This represents the first naturally evolved glyphosate-degrading machinery reported in plants. Here, we report the three-dimensional structure of these two AKR enzymes in complex with cofactor by performing X-ray crystallography. Furthermore, the binding-mode of glyphosate were elucidated in a ternary complex of AKR4C17. Based on the structural information and the previous study, we proposed a possible mechanism of action of AKR-mediated glyphosate degradation. In addition, a variant F291D of AKR4C17 that was constructed based on structure-based engineering showed a 70% increase in glyphosate degradation. In conclusion, these results demonstrate the structural features and glyphosate-binding mode of AKR4C17, which increases our understanding of the enzymatic mechanism of glyphosate bio-degradation and provides an important basis for the designation of AKR-based glyphosate-resistance for further applications.

Microbiomes and glyphosate biodegradation in edaphic and aquatic environments: recent issues and trends.

Glyphosate (N-(phosphonomethyl)glycine) has emerged as the top-selling herbicide worldwide because of its versatility in controlling annual and perennial weeds and the extensive use of glyphosate-resistant crops. Concerns related to the widespread use of glyphosate and its ubiquitous presence in the environment has led to a large number of studies and reviews, which examined the toxicity and fate of glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA) in the environment. Because the biological breakdown of glyphosate is most likely the main elimination process, the biodegradation of glyphosate has also been the object of abundant experimental work. Importantly, glyphosate biodegradation in aquatic and soil ecosystems is affected not only by the composition and the activity of microbial communities, but also by the physical environment. However, the interplay between microbiomes and glyphosate biodegradation in edaphic and aquatic environments has rarely been considered before. The proposed minireview aims at filling this gap. We summarize the most recent work exploring glyphosate biodegradation in natural aquatic biofilms, the biological, chemical and physical factors and processes playing on the adsorption, transport and biodegradation of glyphosate at different levels of soil organization and under different agricultural managements, and its impact on soil microbial communities.

History of Herbicide-Resistant Traits in Cotton in the U.S. and the Importance of Integrated Weed Management for Technology Stewardship.

This paper reviews the history of herbicide-resistant (HR) traits in U.S. cotton since the beginning, highlighting the shortcomings of each trait over time that has led to the development of their successor and emphasizing the importance of integrated weed management (IWM) going forward to ensure their long-term sustainability. Introduction of glyphosate-resistant cropping systems has allowed for expansion of no-till systems more reliant on herbicides, favored less diverse crop rotations, and heavily relied on a single herbicide mode of action (MOA). With repeated applications of glyphosate over the years, biotypes of glyphosate-resistant (GR) A. palmeri and other weeds became economically damaging pests in cotton production systems throughout the U.S. Moreover, the reported cases of weeds resistant to different MOA across various parts of the United States has increased. The dicamba- (XtendFlex®) and 2,4-D-resistant (Enlist®) cotton traits (with stacks of glyphosate and glufosinate resistance) were introduced and have been highly adopted in the U.S. to manage HR weeds. Given the current rate of novel herbicide MOA discovery and increase in new HR weed cases, the future of sustainable weed management relies on an integrated approach that includes non-herbicidal methods with herbicides to ensure long-term success.