Herbicides: History, Classification and Genetic Manipulation of Plants for Herbicide Resistance

Unlocking the potential of glyphosate-resistant bacterial strains in biodegradation and maize growth

Glyphosate [N-(phosphonomethyl)-glycine] is a non-selective herbicide with a broad spectrum activity that is commonly used to control perennial vegetation in agricultural fields. The widespread utilization of glyphosate in agriculture leads to soil, water, and food crop contamination, resulting in human and environmental health consequences. Therefore, it is imperative to devise techniques for enhancing the degradation of glyphosate in soil. Rhizobacteria play a crucial role in degrading organic contaminants. Limited work has been done on exploring the capabilities of indigenously existing glyphosate-degrading rhizobacteria in Pakistani soils. This research attempts to discover whether native bacteria have the glyphosate-degrading ability for a sustainable solution to glyphosate contamination. Therefore, this study explored the potential of 11 native strains isolated from the soil with repeated glyphosate application history and showed resistance against glyphosate at higher concentrations (200 mg kg-1). Five out of eleven strains outperformed in glyphosate degradation and plant growth promotion. High-pressure liquid chromatography showed that, on average, these five strains degraded 98% glyphosate. In addition, these strains promote maize seed germination index and shoot and root fresh biomass up to 73 and 91%, respectively. Furthermore, inoculation gave an average increase of acid phosphatase (57.97%), alkaline phosphatase (1.76-fold), and dehydrogenase activity (1.75-fold) in glyphosate-contaminated soil. The findings indicated the importance of using indigenous rhizobacteria to degrade glyphosate. Therefore, by maintaining soil health, indigenous soil biodiversity can work effectively for the bioremediation of contaminated soils and sustainable crop production in a world facing food security.

Genetic modification strategies for enhancing plant resilience to abiotic stresses in the context of climate change

Enhancing the resilience of plants to abiotic stresses, such as drought, salinity, heat, and cold, is crucial for ensuring global food security challenge in the context of climate change. The adverse effects of climate change, characterized by rising temperatures, shifting rainfall patterns, and increased frequency of extreme weather events, pose significant threats to agricultural systems worldwide. Genetic modification strategies offer promising approaches to develop crops with improved abiotic stress tolerance. This review article provides a comprehensive overview of various genetic modification techniques employed to enhance plant resilience. These strategies include the introduction of stress-responsive genes, transcription factors, and regulatory elements to enhance stress signaling pathways. Additionally, the manipulation of hormone signaling pathways, osmoprotectant accumulation, and antioxidant defense mechanisms is discussed. The use of genome editing tools, such as CRISPR-Cas9, for precise modification of target genes related to stress tolerance is also explored. Furthermore, the challenges and future prospects of genetic modification for abiotic stress tolerance are highlighted. Understanding and harnessing the potential of genetic modification strategies can contribute to the development of resilient crop varieties capable of withstanding adverse environmental conditions caused by climate change, thereby ensuring sustainable agricultural productivity and food security.

Methylglyoxal detoxification pathway - Explored first time for imazethapyr tolerance in lentil (Lens culinaris L.)

Lentil is an important pulses crop but it's short stature and slow growth rate make it vulnerable to weed competition, limiting crop productivity. There is need to identify herbicide tolerant genotypes and their tolerance mechanism. The present investigation was conducted to understand the effect of imazethapyr (IM) treatment on accumulation of methylglyoxal (MG) and its detoxification mechanism in IM-tolerant (LL1397 and LL1612) susceptible (FLIP2004-7L and PL07) genotypes sown under control (weed free), weedy check (weeds were growing with crop) and sprayed with imazethapyr. The enzymes of glyoxalase pathway (glyoxalase I, II and III) and non glyoxalase pathway (methylglyoxal reductase), lactate dehydrogenase (LDH), glutathione content, gamma-glutamyl-cysteine synthetase (γ-GCS) were estimated in lentil genotypes at different days after spray. Higher activities of glyoxalase I, II and III and MGR along with the increased glutathione content (GSH) content in LL1397 and LL1612 under IM treatment as compared to FLIP2004-7L and PL07 might be responsible for lowering MG accumulation and increasing lactate content, which is end product of these pathways. Enhanced LDH activity in LL1397 and LL1612 might be responsible for energy production via TCA cycle that might be responsible for growth and recovery of tolerant genotypes after IM treatment. Higher γ-GCS activity in tolerant genotypes led to increased glutathione content required for glyoxalase pathway. However, decreased activities of glyoxalase enzymes and MGR in susceptible genotypes result in MG accumulation which limit plant growth. This is the first ever study elucidating the role of MG detoxification pathway conferring IM tolerance in lentil.

Proteomic Profile of Glyphosate-Resistant Soybean under Combined Herbicide and Drought Stress Conditions

While some genetically modified (GM) plants have been targeted to confer tolerance to abiotic stressors, transgenes are impacted by abiotic stressors, causing adverse effects on plant physiology and yield. However, routine safety analyses do not assess the response of GM plants under different environmental stress conditions. In the context of climate change, the combination of abiotic stressors is a reality in agroecosystems. Therefore, the aim of this study was to analyze the metabolic cost by assessing the proteomic profiles of GM soybean varieties under glyphosate spraying and water deficit conditions compared to their non-transgenic conventional counterparts. We found evidence of cumulative adverse effects that resulted in the reduction of enzymes involved in carbohydrate metabolism, along with the expression of amino acids and nitrogen metabolic enzymes. Ribosomal metabolism was significantly enriched, particularly the protein families associated with ribosomal complexes L5 and L18. The interaction network map showed that the affected module representing the ribosome pathway interacts strongly with other important proteins, such as the chloro-plastic gamma ATP synthase subunit. Combined, these findings provide clear evidence for increasing the metabolic costs of GM soybean plants in response to the accumulation of stress factors. First, alterations in the ribosome pathway indicate that the GM plant itself carries a metabolic burden associated with the biosynthesis of proteins as effects of genetic transformation. GM plants also showed an imbalance in energy demand and production under controlled conditions, which was increased under drought conditions. Identifying the consequences of altered metabolism related to the interaction between plant transgene stress responses allows us to understand the possible effects on the ecology and evolution of plants in the medium and long term and the potential interactions with other organisms when these organisms are released in the environment.

In Silico Resources of Drug-Likeness as a Mirror: What Are We Lacking in Pesticide-Likeness?

Unfavorable bioavailability is an important aspect underlying the failure of drug candidates. Computational approaches for evaluating drug-likeness can minimize these risks. Over the past decades, computational approaches for evaluating drug-likeness have sped up the process of drug development and were also quickly derived to pesticide-likeness. As a result of many critical differences between drugs and pesticides, many kinds of methods for drug-likeness cannot be used for pesticide-likeness. Therefore, it is crucial to comprehensively compare and analyze the differences between drug-likeness and pesticide-likeness, which may provide a basis for solving the problems encountered during the evaluation of pesticide-likeness. Here, we systematically collected the recent advances of drug-likeness and pesticide-likeness and compared their characteristics. We also evaluated the current lack of studies on pesticide-likeness, the molecular descriptors and parameters adopted, the pesticide-likeness model on pesticide target organisms, and comprehensive analysis tools. This work may guide researchers to use appropriate methods for developing pesticide-likeness models. It may also aid non-specialists to understand some important concepts in drug-likeness and pesticide-likeness.

Phytotoxic bioassays and Fingerprinting by HPLC-DAD of Eragrostis plana Nees Root Extracts - application of chemometrics

Eragrostis plana (Nees) (Tough Lovegrass) shows ability to interfere with other plants, a phenomenon known as allelopathy. This chemical interaction between plants occurs due to the release of compounds into the environment. Thus, a phytotoxicity study was carried out with E. plana roots collected during each season throughout the year, and the compounds were extracted with solvents of increasing polarity. The data from the bioassays were analyzed by GLM and PCA. In addition, a fingerprint of these extracts was obtained by HPLC-DAD. The extracts in petroleum ether from roots collected in the winter and summer showed greater phytotoxicity on Ipomoea grandifolia germination and growth. The PCA obtained from the chromatogram of the crude extract showed that the extracts in petroleum ether were chemically different from the extracts in ethyl acetate and methanol. Thus, continuing this study in order to develop a new generation of bio-herbicides is essential.

Herbicide Resistance: Another Hot Agronomic Trait for Plant Genome Editing

Weeds have continually interrupted crop plants since their domestication, leading to a greater yield loss compared to diseases and pests that necessitated the practice of weed control measures. The control of weeds is crucial to ensuring the availability of sufficient food for a rapidly increasing human population. Chemical weed control (herbicides) along with integrated weed management (IWM) practices can be the most effective and reliable method of weed management programs. The application of herbicides for weed control practices calls for the urgency to develop herbicide-resistant (HR) crops. Recently, genome editing tools, especially CRISPR-Cas9, have brought innovation in genome editing technology that opens up new possibilities to provide sustainable farming in modern agricultural industry. To date, several non-genetically modified (GM) HR crops have been developed through genome editing that can present a leading role to combat weed problems along with increasing crop productivity to meet increasing food demand around the world. Here, we present the chemical method of weed control, approaches for herbicide resistance development, and possible advantages and limitations of genome editing in herbicide resistance. We also discuss how genome editing would be effective in combating intensive weed problems and what would be the impact of genome-edited HR crops in agriculture.

Review: amino acid biosynthesis as a target for herbicide development

There are three amino acid biosynthesis pathways that are targeted by current herbicides, namely those leading to the production of aromatic amino acids, branched chain amino acids and glutamine. However, their efficacy is diminishing as a result of the increasing number of resistant weeds. Indeed, resistance to most classes of herbicides is on the rise, posing a significant threat to the utility of current herbicides to sustain effective weed management. This review provides an overview of potential herbicide targets within amino acid biosynthesis that remain unexploited commercially, and recent inhibitor discovery efforts. Despite contemporary approaches to herbicide discovery, such as chemical repurposing and the use of omics technologies, there have been no new products introduced to the market that inhibit amino acid biosynthesis over the past three decades. This highlights the chasm that exists between identifying a potent inhibitor and introducing a commercial herbicide. The unpredictability of a mode of action at the systemic level, as well as poor physicochemical properties, often contribute to a lack of progression beyond the target inhibition stage. Nevertheless, it will be important to overcome these obstacles for the development of new herbicides to protect our agricultural industry and ensure food security for an increasing world population. © 2020 Society of Chemical Industry.

Ionic Liquids in Agrochemistry

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In this review article, we present the latest research in the field of ionic liquids containing biologically active anions and cations, their potential application in the field of agrochemistry and agriculture. The article describes examples of the use of ionic liquids as herbicides, fungicides, antimicrobial agents, deterrents and plant growth stimulants. It also indicates the advantages and disadvantages of using ionic liquids, such as their multitasking, toxicity, thermal stability and solubility in water in comparison with commercial chemicals. Readers will find in the article the prospects for the use of ionic liquids in agriculture, as well as the high value of using ILs as multifunctional biologically active substances.

Encapsulated Limonene: A Pleasant Lemon-Like Aroma with Promising Application in the Agri-Food Industry. A Review

Limonene, mainly found as a major component in Citrus spp., has been proven to possess a valuable potential as sustainable replacement to synthetic pesticides and food preservatives. This review intends to give a clear overview of the principal emerging applications of limonene in the agri-food industry as antimicrobial, herbicidal and antioxidant agent. To successfully use limonene in a greener agri-food industry, its preservation had become a top concern for manufacturers. In order to elucidate the most efficient and sustainable manner to encapsulate limonene, the different techniques and materials tested up to the present are also reviewed. In general, encapsulation conserves and protects limonene from outside aggressions, but also allows its controlled release as well as enhances its low water solubility, which can be critical for the discussed applications. Other parameters such as scalability, low cost and availability of equipment will need to be taken into account. Further efforts would likely be oriented to the elucidation of encapsulating sustainable systems obtained by cost-efficient elaboration processes, which can deliver effective concentrations of limonene without affecting crops and food products.

Multidimensional relationships of herbicides with insect-crop food webs

Controlling weeds is critical for improving the yield and quality of crops. Herbicides are the most commonly applied pesticides in agro-ecosystems. Herbicides affect insects directly as contact damage and indirectly by influencing food supplies. The innate susceptibility, life stages, and mode of feeding of insects can affect the herbicide-insect interaction. Interaction of herbicides with insect pest and beneficial insects is mainly indirect and absence of weeds either can reduce the insect population or causes switching of host plant and hence can also increase the population. The direct effect of herbicides depends on carrier or surfactant used. Presence of herbicides also provides surfactant to insecticides and increases impact of insecticides. At present, most reports on impact of herbicides indicate alterations in insect survival or egg production due to increase or decrease in host plant population as an indirect affect, only a handful studies reported a direct topical effect of these herbicides on egg, larvae/nymphs and adults of various insects. Further exploration of this interaction seems intriguing. Use of bio-herbicides, cultural control methods, and judicious use of herbicides could offer ecologically sustainable approaches to reduce impact of herbicides on insects.

Overexpressing Exogenous 5-Enolpyruvylshikimate-3-Phosphate Synthase (EPSPS) Genes Increases Fecundity and Auxin Content of Transgenic Arabidopsis Plants

Transgenic glyphosate-tolerant plants overproducing EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) may exhibit enhanced fitness in glyphosate-free environments. If so, introgression of transgenes overexpressing EPSPS into wild relative species may lead to increased competitiveness of crop-wild hybrids, resulting in unpredicted environmental impact. Assessing fitness effects of transgenes overexpressing EPSPS in a model plant species can help address this question, while elucidating how overproducing EPSPS affects the fitness-related traits of plants. We produced segregating T₂ and T₃Arabidopsis thaliana lineages with or without a transgene overexpressing EPSPS isolated from rice or Agrobacterium (CP4). For each of the three transgenes, we compared glyphosate tolerance, some fitness-related traits, and auxin (indole-3-acetic acid) content in transgene-present, transgene-absent, empty vector (EV), and parental lineages in a common-garden experiment. We detected substantially increased glyphosate tolerance in T₂ plants of transgene-present lineages that overproduced EPSPS. We also documented significant increases in fecundity, which was associated with increased auxin content in T₃ transgene-present lineages containing rice EPSPS genes, compared with their segregating transgene-absent lineages, EV, and parental controls. Our results from Arabidopsis with nine transgenic events provide a strong support to the hypothesis that transgenic plants overproducing EPSPS can benefit from a fecundity advantage in glyphosate-free environments. Stimulated biosynthesis of auxin, an important plant growth hormone, by overproducing EPSPS may play a role in enhanced fecundity of the transgenic Arabidopsis plants. The obtained knowledge is useful for assessing environmental impact caused by introgression of transgenes overproducing EPSPS from any GE crop into populations of its wild relatives.