A novel triple amino acid substitution in the EPSPS found in a high‐level glyphosate‐resistant Amaranthus hybridus population from Argentina (original) (raw)
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Pest Management Science, 2018
BACKGROUND: The evolution of herbicide-resistant weeds is one of the most important concerns of the global agriculture. Amaranthus hybridus L. is a competitive weed for summer crops in South America. In this article, we intend to unravel the molecular mechanisms by which an A. hybridus population from Argentina has become resistant to extraordinarily high levels of glyphosate. RESULTS: The glyphosate resistant population ("A") exhibited particularly high parameters of resistance (GR 50 = 20900 g ai ha-1 , Rf= 314), with all plants completing a normal life cycle even after 32X dose application. No shikimic acid accumulation was detected in the resistant plants at any of the glyphosate concentrations tested. Molecular and genetic analyses revealed a novel triple substitution (TAP-IVS: T102I, A103V, and P106S) in the EPSPS enzyme of population "A" and an incipient increase on the epsps relative copy number but without effects on the epsps transcription levels. The novel mechanism was prevalent, with 48% and 52% of the individuals being homozygous and heterozygous for the triple substitution, respectively. In silico conformational studies revealed that TAP-IVS triple substitution would generate an EPSPS with a functional active site but with an increased restriction to the glyphosate binding. CONCLUSION: The prevalence of the TAP-IVS triple substitution as the solely mechanism detected in the highly glyphosate resistant population suggest the evolution of a new GR mechanism arising in A. hybridus. This is the first report of a naturally-occurring EPSPS triple substitution and the first glyphosate TSR mechanism described in A. hybridus.
Genomic distribution of EPSPS copies conferring glyphosate resistance in Palmer amaranth and kochia
Indian Journal of Weed Science, 2016
Palmer amaranth and kochia are major problem weeds in many cropping systems in the United States. Wide acceptance of glyphosate tolerant crop technology has resulted in extensive use of glyphosate, consequently, a number of weeds including Palmer amaranth and kochia evolved resistance to glyphosate throughout the US. Within a span of 5-7 years the glyphosate resistance in these weeds has spread extensively, devastating several major crops. Understanding the mechanisms of herbicide resistance is valuable to determine the level of resistance as well as how the resistance spreads in the populations. Glyphosate resistance mechanisms in Palmer amaranth and kochia have been investigated extensively. Although resistance to glyphosate has evolved as a result of amplification of 5enolpyruvylshikimtate-3-phosphate synthase (EPSPS), the target site of glyphosate, but the distribution and configuration of amplified copies of EPSPS gene in the genomes of these two species is different. The EPSPS gene amplification may have possibly mediated by transposons in Palmer amaranth and whereas, likely to have resulted because of unequal recombination in kochia. These findings suggest that the EPSPS amplification can occur via different mechanisms in different weeds. Evolution of glyphosate resistance as a result of EPSPS gene amplification is a threat to long-term sustainability of glyphosate-resistant crop technology.
Journal of Agricultural and Food Chemistry, 2011
Glyphosate resistance evolution in weeds is a growing problem in world agriculture. Here, we have investigated the mechanism(s) of glyphosate resistance in a Lolium rigidum population (DAG1) from South Africa. Nucleotide sequencing revealed the existence of at least three EPSPS homologues in the L. rigidum genome and identified a novel proline 106 to leucine substitution (P106L) in 52% DAG1 individuals. This mutation conferred a 1.7-fold resistance increase to glyphosate at the whole plant level. Additionally, a 3.1-fold resistance increase, not linked to metabolism or translocation, was estimated between wild-type P106-DAG1 and P106-STDS sensitive plants. Point accepted mutation analysis suggested that other amino acid substitutions at EPSPS position 106 are likely to be found in nature besides the P106/S/A/T/L point mutations reported to date. This study highlights the importance of minor mechanisms acting additively to confer significant levels of resistance to commercial field rates of glyphosate in weed populations subjected to high selection pressure.
Molecular basis of glyphosate resistance - different approaches through protein engineering
FEBS Journal, 2011
Glyphosate (N-phosphonomethyl-glycine) is the most-used herbicide in the world: glyphosatebased formulations exhibit broad-spectrum herbicidal activity with minimal human and environmental toxicity. The extraordinary success of this simple small molecule is mainly due to the high specificity of glyphosate towards the plant enzyme enolpyruvylshikimate-3-phosphate synthase in the shikimate pathway leading to biosynthesis of aromatic amino acids. Starting in 1996, transgenic glyphosate-resistant plants were introduced thus allowing the application of the herbicide to the crop (post-emergence) to remove emerged weeds without crop damage. This review focuses on the evolution of mechanisms of resistance to glyphosate as obtained through natural diversity, the gene shuffling approach to molecular evolution, and a rational, structurebased approach to protein engineering. In addition, we offer rationale for the means by which the modifications made have had their intended effect.
Glyphosate resistance: state of knowledge
Studies of mechanisms of resistance to glyphosate have increased current understanding of herbicide resistance mechanisms. Thus far, single-codon non-synonymous mutations of EPSPS (5-enolypyruvylshikimate-3-phosphate synthase) have been rare and, relative to other herbicide mode of action target-site mutations, unconventionally weak in magnitude for resistance to glyphosate. However, it is possible that weeds will emerge with non-synonymous mutations of two codons of EPSPS to produce an enzyme endowing greater resistance to glyphosate. Today, target-gene duplication is a common glyphosate resistance mechanism and could become a fundamental process for developing any resistance trait. Based on competition and substrate selectivity studies in several species, rapid vacuole sequestration of glyphosate occurs via a transporter mechanism. Conversely, as the chloroplast requires transporters for uptake of important metabolites, transporters associated with the two plastid membranes may separately, or together, successfully block glyphosate delivery. A model based on finite glyphosate dose and limiting time required for chloroplast loading sets the stage for understanding how uniquely different mechanisms can contribute to overall glyphosate resistance.
Pest management science, 2014
Echinochloa colona is an annual weed affecting field crops and orchards in California. An E. colona population carrying a mutation in the EPSPS gene endowing resistance to glyphosate, the most widely used non-selective herbicide, was recently identified in the Northern Sacramento Valley of California. Plants from this population, from a suspected glyphosate-resistant (GR) population, and from one susceptible (S) population collected in the Northern Sacramento Valley of California, were used to generate three GR and one S selfed lines to study possible mechanisms involved in glyphosate resistance. Based on the amount of glyphosate required to kill 50% of the plants (LD50 ), GR lines were 4-9-fold more resistant than S plants and accumulated less shikimate after glyphosate treatment. GR and S lines did not differ in glyphosate absorption, translocation or metabolism. A different target-site mutation was found in each of two of the GR lines corresponding to Pro106Thr and Pro106Ser subs...
Plant physiology, 2015
Glyphosate is the most important and widely used herbicide in world agriculture. Intensive glyphosate selection has resulted in the widespread evolution of glyphosate-resistant weed populations, threatening the sustainability of this valuable once-in-a-century agrochemical. Field-evolved glyphosate resistance due to known resistance mechanisms is generally low to modest. Here, working with a highly glyphosate-resistant Eleusine indica population, we identified a double amino acid substitution (T102I + P106S [TIPS]) in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene in glyphosate-resistant individuals. This TIPS mutation recreates the biotechnology-engineered commercial first generation glyphosate-tolerant EPSPS in corn (Zea mays) and now in other crops. In E. indica, the naturally evolved TIPS mutants are highly (more than 180-fold) resistant to glyphosate compared with the wild type and more resistant (more than 32-fold) than the previously known P106S mutants. The E. ...