Journal articles: 'EPSPS target-site mutation'

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Chaudhari, Sushila, Vijay K. Varanasi, Sridevi Nakka, Prasanta C. Bhowmik, Curtis R. Thompson, Dallas E. Peterson, Randall S. Currie, and Mithila Jugulam. "Evolution of target and non-target based multiple herbicide resistance in a single Palmer amaranth (Amaranthus palmeri) population from Kansas." Weed Technology 34, no. 3 (June 2020): 447–53. http://dx.doi.org/10.1017/wet.2020.32.

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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.

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Li, Jinyao, Yu Mei, Lingling Zhang, Lubo Hao, and Mingqi Zheng. "The Resistance Levels and Target-Site Based Resistance Mechanisms to Glyphosate in Eleusine indica from China." Agronomy 12, no. 11 (November 9, 2022): 2780. http://dx.doi.org/10.3390/agronomy12112780.

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The Dongting and Poyang Lakes are the important rice growing areas, and the Bohai Rim and Loess Plateau are the main producing areas of apples in China, where glyphosate has been used continuously to control weeds including Eleusine. indica for many years. In this study, the resistance levels and target-site based resistance (TSR) mechanisms to glyphosate in E. indica populations, which were collected from above areas were investigated. A total of 35 out of 50 (70%) E. indica populations have evolved resistance to glyphosate with resistance index (RI) of 2.01~10.43. The glyphosate-resistant (GR) E. indica accumulated less shikimic acid than glyphosate-susceptible (GS) populations, when treated by 1.0 mg/L, 10 mg/L or 100 mg/L glyphosate. There was no mutation at Thr102 and Pro106 in 5-enolpyruvate shikimate-3-phosphate synthase (EPSPS), which endowed glyphosate resistance in E. indica and other weed species. A Pro-381-Leu was found in EPSPS in GR populations. In contrast, the expression level of EPSPS gene was highly correlated with glyphosate resistance in E. indica with a Pearson coefficient of 0.73. These indicate that the glyphosate resistance in aforementioned E. indica populations was mainly caused by the overexpression of EPSPS, not by amino acid mutation in EPSPS.

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Salgotra, Romesh, and Bhagirath Singh Chauhan. "The First Report of Target-Site Resistance to Glyphosate in Sweet Summer Grass (Moorochloa eruciformis)." Plants 10, no. 9 (September 11, 2021): 1885. http://dx.doi.org/10.3390/plants10091885.

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Sweet summer grass is a problematic weed in the central Queensland region of Australia. This study found glyphosate resistance in two biotypes (R1 and R2) of sweet summer grass. The level of resistance in these biotypes was greater than 8-fold. The glyphosate dose required to reduce dry matter by 50% (GR50) for the resistant populations varied from 1993 to 2100 g ha−1. A novel glyphosate resistance double point mutation in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene was identified for the first time in sweet summer grass. Multiple mutations, including multiple amino acid changes at the glyphosate target site, as well as mutations involving two nucleotide changes at a single amino acid codon, were observed. Both resistant biotypes exhibited a nucleotide change of CAA to ACA in codon 106, which predicts an amino acid change of proline to a threonine (Pro-106-Thr). In addition, the R1 biotype also possessed a mutation at codon 100, where a nucleotide substitution of T for G occurred (GCT to TCT), resulting in a substitution of serine for alanine (Ala-100-Ser). Understanding the molecular mechanism of glyphosate resistance will help to design effective management strategies to control invasive weeds.

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Moehs, Charles P., William J. Austill, Daniel Facciotti, Aaron Holm, Dayna Loeffler, Zhongjin Lu, Jessica C. Mullenberg, et al. "Development of non-transgenic glyphosate tolerant wheat by TILLING." PLOS ONE 16, no. 9 (September 15, 2021): e0245802. http://dx.doi.org/10.1371/journal.pone.0245802.

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Glyphosate (N-phosphonomethyl-glycine) is the world’s most widely used broad spectrum, post-emergence herbicide. It inhibits the chloroplast-targeted enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS; EC 2.5.1.19), a component of the plant and microorganism-specific shikimate pathway and a key catalyst in the production of aromatic amino acids. Variants of EPSPS that are not inhibited by glyphosate due to particular amino acid alterations in the active site of the enzyme are known. Some of these variants have been identified in weed species that have developed resistance to glyphosate because of the strong selective pressure of continuous, heavy glyphosate use. We have used TILLING (Targeting Induced Local Lesions in Genomes), a non-transgenic, target-selected, reverse genetics, mutation breeding technique, and conventional genetic crosses, to identify and combine, through two rounds of mutagenesis, wheat lines having both T102I and P106S (so-called TIPS enzyme) mutations in both the A and the D sub-genome homoeologous copies of the wheat EPSPS gene. The combined effects of the T102I and P106S mutations are known from previous work in multiple species to minimize the binding of the herbicide while maintaining the affinity of the catalytic site for its native substrates. These novel wheat lines exhibit substantial tolerance to commercially relevant levels of glyphosate.

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Kaundun, Shiv S., Ian A. Zelaya, Richard P. Dale, Amy J. Lycett, Patrice Carter, Kate R. Sharples, and Eddie McIndoe. "Importance of the P106S Target-Site Mutation in Conferring Resistance to Glyphosate in a Goosegrass (Eleusine indica) Population from the Philippines." Weed Science 56, no. 5 (October 2008): 637–46. http://dx.doi.org/10.1614/ws-07-148.1.

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Few studies on herbicide resistance report data to establish unambiguously the correlation between genotype and phenotype. Here we report on the importance of the EPSPS prolyl106point mutation to serine (P106S) in conferring resistance to glyphosate in a goosegrass population from Davao, Mindanao Island, the Philippines (Davao). Initial rate-response studies showed clear survivors within the Davao population at glyphosate rates that completely controlled the standard sensitive goosegrass population (STD1). Assessment of potential resistance mechanisms identified the presence of P106S mutant individuals in the Davao population. Polymerase chain reaction (PCR) amplification of specific alleles (PASA) analysis established that the mixed-resistant Davao population was comprised of 39.1% homozygous proline wild-type (PP106), 3.3% heterozygous serine mutant (PS106), and 57.6% homozygous serine mutant (SS106) genotypes. Further rate-response studies on plants with a predetermined genotype estimated the Davao SS106 individuals to be approximately 2-fold more resistant to glyphosate compared to Davao PP106 individuals. Extensive analysis at different goosegrass growth stages and glyphosate rates established strong correlation (P < 0.001) between presence of P106S in EPSPS and the resistant phenotype. Importantly, no differences in the pattern of absorbed or translocated14C–glyphosate were observed between PP106 and SS106 Davao genotypes or Davao and STD1 individuals, suggesting that glyphosate resistance in the Davao population was attributable to an altered target site mechanism. This study demonstrates that whilst P106S in EPSPS confers a moderate resistance level to glyphosate, the mechanism is sufficient to endow glyphosate failure at the recommended field rates.

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Chatham, Laura A., Kevin W. Bradley, Greg R. Kruger, James R. Martin, Micheal D. K. Owen, Dallas E. Peterson, Jugulam Mithila, and Patrick J. Tranel. "A Multistate Study of the Association Between Glyphosate Resistance and EPSPS Gene Amplification in Waterhemp (Amaranthus tuberculatus)." Weed Science 63, no. 3 (September 2015): 569–77. http://dx.doi.org/10.1614/ws-d-14-00149.1.

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Waterhemp is an increasingly problematic weed in the U.S. Midwest, having now evolved resistances to herbicides from six different site-of-action groups. Glyphosate-resistant waterhemp in the Midwest is especially concerning given the economic importance of glyphosate in corn and soybean production. Amplification of the target-site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) was found to be the mechanism of glyphosate resistance in Palmer amaranth, a species closely related to waterhemp. Here, the relationship between glyphosate resistance and EPSPS gene amplification in waterhemp was investigated. Glyphosate dose response studies were performed at field sites with glyphosate-resistant waterhemp in Illinois, Kansas, Kentucky, Missouri, and Nebraska, and relative EPSPS copy number of survivors was determined via quantitative real-time polymerase chain reaction (qPCR). Waterhemp control increased with increasing glyphosate rate at all locations, but no population was completely controlled even at the highest rate (3,360 g ae ha−1). EPSPS gene amplification was present in plants from four of five locations (Illinois, Kansas, Missouri, and Nebraska) and the proportion of plants with elevated copy number was generally higher in survivors from glyphosate-treated plots than in plants from the untreated control plots. Copy number magnitude varied by site, but an overall trend of increasing copy number with increasing rate was observed in populations with gene amplification, suggesting that waterhemp plants with more EPSPS copies are more resistant. Survivors from the Kentucky population did not have elevated EPSPS copy number. Instead, resistance in this population was attributed to the EPSPS Pro106Ser mutation. Results herein show a quantitative relationship between glyphosate resistance and EPSPS gene amplification in some waterhemp populations, while highlighting that other mechanisms also confer glyphosate resistance in waterhemp.

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Kaundun, Jackson, Hutchings, Galloway, Marchegiani, Howell, Carlin, Mcindoe, Tuesca, and Moreno. "Evolution of Target-Site Resistance to Glyphosate in an Amaranthus palmeri Population from Argentina and Its Expression at Different Plant Growth Temperatures." Plants 8, no. 11 (November 16, 2019): 512. http://dx.doi.org/10.3390/plants8110512.

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The mechanism and expression of resistance to glyphosate at different plant growing temperatures was investigated in an Amaranthus palmeri population (VM1) from a soybean field in Vicuña Mackenna, Cordoba, Argentina. Resistance was not due to reduced glyphosate translocation to the meristem or to EPSPS duplication, as reported for most US samples. In contrast, a proline 106 to serine target-site mutation acting additively with EPSPS over-expression (1.8-fold increase) was respectively a major and minor contributor to glyphosate resistance in VM1. Resistance indices based on LD50 values generated using progenies from a cross between 52 PS106 VM1 individuals were estimated at 7.1 for homozygous SS106 and 4.3 for heterozygous PS106 compared with homozygous wild PP106 plants grown at a medium temperature of 24 °C day/18 °C night. A larger proportion of wild and mutant progenies survived a single commonly employed glyphosate rate when maintained at 30 °C day/26 °C night compared with 20 °C day/16 night in a subsequent experiment. Interestingly, the P106S mutation was not identified in any of the 920 plants analysed from 115 US populations, thereby potentially reflecting the difference in A. palmeri control practices in Argentina and USA.

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Okumu, Martha N., Petrus J. Robbertse, Barend J. Vorster, and Carl F. Reinhardt. "The Molecular, Morphological and Genetic Characterization of Glyphosate Resistance in Conyza bonariensis from South Africa." Plants 11, no. 21 (October 24, 2022): 2830. http://dx.doi.org/10.3390/plants11212830.

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Six Conyza bonariensis (L.) Cronquist populations were screened in a pot experiment at the University of Pretoria’s Hatfield experimental farm to evaluate and confirm the degree of glyphosate response. Resistance factors ranged from 2.7- to 24.8-fold compared to the most susceptible biotype. Partial sequencing of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene found no mutation at the Thr102, Ala103 or Pro106 positions. EPSPS mRNA expression levels in glyphosate-resistant biotypes (Swellendam and Piketberg seed sampling sites) were comparable or lower than those in susceptible biotypes (George and Fauresmith sites). Additionally, the highest expression level was reported in the susceptible Fauresmith biotype. These results indicate that glyphosate resistance in the tested resistant biotypes is not caused by target-site mutations and EPSPS gene amplification. Leaf surface characteristics can influence the spread and subsequent absorption of glyphosate. The study established non-significant results in the amount of leaf wax and insufficient mean separations in cuticle thickness and trichome density data. Therefore, the observed differences in response of biotypes to glyphosate treatment could not be attributed conclusively to differences in the leaf morphological characteristics investigated. Results from the inheritance study were consistent with glyphosate resistance being inherited in an incompletely dominant manner when plants were treated with glyphosate herbicide at 900 g ae ha−1.

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Kutasy, Barbara, Zoltán Farkas, Balázs Kolics, Kincső Decsi, Géza Hegedűs, Judit Kovács, János Taller, et al. "Detection of Target-Site Herbicide Resistance in the Common Ragweed: Nucleotide Polymorphism Genotyping by Targeted Amplicon Sequencing." Diversity 13, no. 3 (March 10, 2021): 118. http://dx.doi.org/10.3390/d13030118.

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Background: The spread of herbicide-resistance Ambrosia artemisiifolia threatens not only the production of agricultural crops, but also the composition of weed communities. The reduction of their spread would positively affect the biodiversity and beneficial weed communities in the arable habitats. Detection of resistant populations would help to reduce herbicide exposure which may contribute to the development of sustainable agroecosystems. Methods: This study focuses on the application of target-site resistance (TSR) diagnostic of A. artemisiifolia caused by different herbicides. We used targeted amplicon sequencing (TAS) on Illumina Miseq platform to detect amino acid changes in herbicide target enzymes of resistant and wild-type plants. Results: 16 mutation points of four enzymes targeted by four herbicide groups, such as Photosystem II (PSII), Acetohydroxyacid synthase (AHAS), 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) and protoporphyrinogen IX oxidase (PPO) inhibitors have been identified in common ragweed populations, so far. All the 16 mutation points were analyzed and identified. Out of these, two mutations were detected in resistant biotypes. Conclusions: The applied next-generation sequencing-targeted amplicon sequencing (NGS-TAS) method on A. artemisiifolia resistant and wild-type populations enable TSR detection of large sample numbers in a single reaction. The NGS-TAS provides information about the evolved herbicide resistance that supports the integrated weed control through the reduction of herbicide exposure which may preserve ecological properties in agroecosystems.

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Alarcón-Reverte, Rocío, Alejandro García, Jaime Urzúa, and Albert J. Fischer. "Resistance to Glyphosate in Junglerice (Echinochloa colona) from California." Weed Science 61, no. 1 (March 2013): 48–54. http://dx.doi.org/10.1614/ws-d-12-00073.1.

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A suspected glyphosate-resistant (R) junglerice population was collected from a glyphosate-R corn field near Durham in northern California where glyphosate had been applied at least twice a year for over 6 yr. Based on the amount of glyphosate required to reduce growth by 50% (ED50), the R population was 6.6 times more R than the susceptible (S) standard population. Based on the glyphosate concentration that inhibits EPSPS by 50% based on shikimate accumulation (I50) in leaf discs, R plants were four times more R than S plants. By 3 d after treatment with 0.42 kg ae ha−1glyphosate, the S population had accumulated approximately five times more shikimate than the R population. No differences in [14C]-glyphosate uptake and translocation were detected between R and S plants. However, partial sequencing of theEPSPSgene revealed a mutation in R plants causing a proline to serine change at EPSPS position 106 (P106S). Our results reveal the first case of a P106S target site mutation associated with glyphosate resistance in junglerice.

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Deng, Wei, Zhiwen Duan, Yang Li, Cheng Peng, and Shuzhong Yuan. "Multiple Resistance Mechanisms Involved in Glyphosate Resistance in Eleusine indica." Plants 11, no. 23 (November 23, 2022): 3199. http://dx.doi.org/10.3390/plants11233199.

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Glyphosate is a non-selective herbicide and is widely used for weed control in non-cultivated land in China. One susceptible (S) and five putative glyphosate-resistant (R1, R2, R3, R4, and R5) Eleusine indica biotypes were selected to investigate their resistance levels and the potential resistance mechanisms. Based on the dose–response assays, the R3 and R5 biotypes showed a low-level (2.4 to 3.5-fold) glyphosate resistance, and the R1, R2, and R4 biotypes exhibited a moderate- to high-level (8.6 to 19.2-fold) resistance, compared with the S biotype. The analysis of the target-site resistance (TSR) mechanism revealed that the P106A mutation and the heterozygous double T102I + P106S mutation were found in the R3 and R4 biotypes, respectively. In addition, the similar EPSPS gene overexpression was observed in the R1, R2, and R5 biotypes, suggesting that additional non-target-site resistance (NTSR) mechanisms may contribute to glyphosate resistance in R1 and R2 biotypes. Subsequently, an RNA-Seq analysis was performed to identify candidate genes involved in NTSR. In total, ten differentially expressed contigs between untreated S and R1 or R2 plants, and between glyphosate-treated S and R1 or R2 plants, were identified and further verified with RT-qPCR. One ATP-binding cassette (ABC) transporter gene, one aldo-keto reductases (AKRs) gene and one cytochrome P450 monooxygenase (CytP450) gene were up-regulated in R1 or R2 plants. These results indicated that EPSPS overexpression, single or double mutation was a common TSR mechanisms in E. indica. Additional NTSR mechanisms could play an essential role in glyphosate resistance. Three genes, ABCC4, AKR4C10, and CYP88, could serve as important candidate genes and deserve further functional studies.

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Takano, Hudson K., Rafael R. Mendes, Leonardo B. Scoz, Ramiro F. Lopez Ovejero, Jamil Constantin, Todd A. Gaines, Philip Westra, Franck E. Dayan, and Rubem S. Oliveira. "Proline-106 EPSPS Mutation Imparting Glyphosate Resistance in Goosegrass (Eleusine indica) Emerges in South America." Weed Science 67, no. 1 (December 18, 2018): 48–56. http://dx.doi.org/10.1017/wsc.2018.71.

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AbstractGlyphosate-resistant (GR) goosegrass [Eleusine indica(L.) Gaertn.] was recently identified in Brazil, but its resistance mechanism was unknown. This study elucidated the resistance mechanism in this species and developed a molecular marker for rapid detection of this target-site resistance trait. The resistance factor for the resistant biotype was 4.4-fold compared with the glyphosate-susceptible (GS) in greenhouse dose–response experiments. This was accompanied by a similar (4-fold) difference in the levels of in vitro andin plantashikimate accumulation in these biotypes. However, there was no difference in uptake, translocation, or metabolism of glyphosate between the GS and GR biotypes. Moreover, both biotypes showed similar values for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) copy number and transcription. Sequencing of a 330-bp fragment of theEPSPSgene identified a single-nucleotide polymorphism that led to a Pro-106-Ser amino acid substitution in the enzyme from the GR biotype. This mutation imparted a 3.8-fold increase in the amount of glyphosate required to inhibit 50% of EPSPS activity, confirming the role of this amino acid substitution in resistance to glyphosate. A quantitative PCR–based genotyping assay was developed for the rapid detection of resistant plants containing this Pro-106-Ser mutation.

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Bostamam, Yazid, Jenna M. Malone, Fleur C. Dolman, Peter Boutsalis, and Christopher Preston. "Rigid Ryegrass (Lolium rigidum) Populations Containing a Target Site Mutation in EPSPS and Reduced Glyphosate Translocation Are More Resistant to Glyphosate." Weed Science 60, no. 3 (September 2012): 474–79. http://dx.doi.org/10.1614/ws-d-11-00154.1.

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Glyphosate is widely used for weed control in the grape growing industry in southern Australia. The intensive use of glyphosate in this industry has resulted in the evolution of glyphosate resistance in rigid ryegrass. Two populations of rigid ryegrass from vineyards, SLR80 and SLR88, had 6- to 11-fold resistance to glyphosate in dose-response studies. These resistance levels were higher than two previously well-characterized glyphosate-resistant populations of rigid ryegrass (SLR77 and NLR70), containing a modified target site or reduced translocation, respectively. Populations SLR80 and SLR88 accumulated less glyphosate, 12 and 17% of absorbed glyphosate, in the shoot in the resistant populations compared with 26% in the susceptible population. In addition, a mutation within the target enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) where Pro106had been substituted by either serine or threonine was identified. These two populations are more highly resistant to glyphosate as a consequence of expressing two different resistance mechanisms concurrently.

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García, Maria J., Candelario Palma-Bautista, Antonia M. Rojano-Delgado, Enzo Bracamonte, João Portugal, Ricardo Alcántara-de la Cruz, and Rafael De Prado. "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 20, no. 10 (May 15, 2019): 2396. http://dx.doi.org/10.3390/ijms20102396.

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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.

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Desai, Het Samir, Michael Thompson, and Bhagirath Singh Chauhan. "Target-Site Resistance to Glyphosate in Chloris Virgata Biotypes and Alternative Herbicide Options for its Control." Agronomy 10, no. 9 (August 27, 2020): 1266. http://dx.doi.org/10.3390/agronomy10091266.

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Due to the overdependence on glyphosate to manage weeds in fallow conditions, glyphosate resistance has developed in various biotypes of several grass weeds, including Chloris virgata Sw. The first case of glyphosate resistance in C. virgata was found in 2015 in Australia, and since then several cases have been confirmed in several biotypes across Australia. Pot studies were conducted with 10 biotypes of C. virgata to determine glyphosate resistance levels. The biotypes were identified as either susceptible, moderately resistant or highly resistant based on the glyphosate dose required to kill 50% of plants. Two glyphosate-susceptible (GS) and two glyphosate-resistant (GR) biotypes were identified by the dose-response study and analyzed for the presence of target-site mutation in the 5–enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. Performance of alternative herbicides to glyphosate as well as the double-knock herbicide approach was evaluated on the two GS (Ch and SGM2) and two GR (SGW2 and CP2) biotypes. Three herbicides, clethodim, haloxyfop and paraquat, were found to be effective (100% control) against all four biotypes when applied at the 4–5 leaf stage. All the sequential herbicide treatments, such as glyphosate followed by paraquat and glufosinate-ammonium followed by paraquat, provided 100% control of all four biotypes of C. virgata. This study identified effective herbicide options for the control of GR C. virgata and showed that target-site mutations were involved in the resistance of two biotypes to glyphosate (SGW2 and CP2). Results could aid farmers in selecting herbicides to manage C. virgata in their fields.

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Bell, Michael S., Aaron G. Hager, and Patrick J. Tranel. "Multiple Resistance to Herbicides from Four Site-of-Action Groups in Waterhemp (Amaranthus tuberculatus)." Weed Science 61, no. 3 (September 2013): 460–68. http://dx.doi.org/10.1614/ws-d-12-00166.1.

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In 2006 and 2007, farmers from two counties in Illinois reported failure to control waterhemp with glyphosate. Subsequent onsite field experiments revealed that the populations might be resistant to multiple herbicides. Greenhouse experiments therefore were conducted to confirm glyphosate resistance, and to test for multiple resistance to other herbicides, including atrazine, acifluorfen, lactofen, and imazamox. In glyphosate dose-response experiments, both populations responded similarly to a previously characterized glyphosate-resistant population (MO1). Both Illinois populations also demonstrated high frequencies of resistance to the acetolactate synthase (ALS) inhibitor, imazamox. Additionally, one of the populations demonstrated high frequencies of resistance to both atrazine and the protoporphyrinogen oxidase (PPO) inhibitor, lactofen. Furthermore, using combinations of sequential and tank-mix herbicide applications, individual plants resistant to herbicides spanning all four site-of-action groups were identified from one population. Molecular experiments were performed to provide an initial characterization of the resistance mechanisms and to provide confirmation of the presence of multiple resistance traits within the two populations. Both populations contained the W574L ALS mutation and the ΔG210 PPO mutation, previously shown to confer resistance to ALS and PPO inhibitors, respectively. Atrazine resistance in both populations is suspected to be metabolism-based, because a triazine target-site mutation was not identified. A P106S EPSPS mutation, previously reported to confer glyphosate resistance, was identified in one population. This mutation was identified in both resistant and sensitive plants from the population; however, and so more research is needed to determine the glyphosate-resistance mechanism(s). This is the first known case of a weed population in the United States possessing multiple resistance to herbicides from four site-of-action groups.

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McElroy, J. Scott, and Nathan D. Hall. "Echinochloa colona with Reported Resistance to Glyphosate Conferred by Aldo-Keto Reductase Also Contains a Pro-106-Thr EPSPS Target Site Mutation." Plant Physiology 183, no. 2 (April 21, 2020): 447–50. http://dx.doi.org/10.1104/pp.20.00064.

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Reinhardt, Carl, Juan Vorster, Anita Küpper, Falco Peter, Adelaide Simelane, Stephanus Friis, Jacques Magson, and Chandrashekar Aradhya. "A nonnative Palmer amaranth (Amaranthus palmeri) population in the Republic of South Africa is resistant to herbicides with different sites of action." Weed Science 70, no. 2 (February 14, 2022): 183–97. http://dx.doi.org/10.1017/wsc.2022.9.

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AbstractPalmer amaranth (Amaranthus palmeri S. Watson) is not native to Africa. Based on the presence and persistence of A. palmeri populations, its invasive status in southern Africa is classified as “naturalized.” Globally, A. palmeri is one of the most troublesome weed species in several crops, including soybean [Glycine max (L.) Merr.], maize (Zea mays L.), and cotton (Gossypium hirsutum L.). Certain populations of A. palmeri in various countries were reported to be resistant to herbicides with different sites of action (SOAs). Two biotypes of A. palmeri in the United States reportedly each have resistance to herbicides representing five different SOAs, and between them a total of eight different SOAs are involved. Resistance mechanisms in these biotypes involve target-site and/or non–target site resistance. Here we characterize a specific A. palmeri population that was found in the Douglas district in South Africa and showed resistance to various herbicide SOAs. Initially, this A. palmeri population was discovered in a glyphosate-tolerant cotton field, where it survived glyphosate treatment. Subsequently, greenhouse experiments were conducted to characterize this A. palmeri population for potential resistance to herbicides of additional SOAs, and molecular analyses were conducted to reveal the mechanisms of herbicide resistance. Results indicated resistance to chlorimuron-ethyl and glyphosate in this population, while <90% control (decreased sensitivity) was observed at the label rate for mesotrione, atrazine, saflufenacil, and S-metolachlor. However, glufosinate, tembotrione, acifluorfen, dicamba, 2,4-D, metribuzin, acetochlor, isoxaflutole, diflufenican, and pyroxasulfone were effective at controlling this population. This profiling of herbicide sensitivity has allowed development of programs to control and potentially minimize the spread of this weed. In addition, molecular analysis of EPSPS revealed the role of higher copy number as a mechanism for glyphosate resistance in this population and a Ser-653-Asn target-site mutation likely conferring resistance to the acetolactate synthase–inhibitor chlorimuron-ethyl. No known target-site mutations were identified for the protoporphyrinogen oxidase–inhibitor group.

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Loddo, Donato, Gaetano Imperatore, Andrea Milani, Silvia Panozzo, Silvia Farinati, Maurizio Sattin, and Giuseppe Zanin. "First Report of Glyphosate-Resistant Biotype of Eleusine Indica (L.) Gaertn. in Europe." Agronomy 10, no. 11 (October 31, 2020): 1692. http://dx.doi.org/10.3390/agronomy10111692.

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Glyphosate-resistant biotypes of Eleusine indica (L.) Gaertn. have been detected in Asia, the Americas but not in Europe. The aim of this study was to evaluate resistance levels and possible target site resistance mechanisms of an E. indica biotype (19-1) collected from a plant nursery in Southern Italy where poor glyphosate efficacy was reported. Two dose-response experiments were conducted to evaluate the sensitivity of biotype 19-1 to glyphosate in comparison with two susceptible checks. 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) sequencing was performed to identify possible mutations conferring the resistance. The susceptible biotypes were completely controlled at the glyphosate recommended field dose of 360 g ae ha−1, while 50% of the plants of biotype 19-1 survived at 1440 g ae ha−1. The resistance index of biotype 19-1 ranged between 5.8 and 7.3 for the response variables of fresh weight reduction and plant survival, respectively. All the plants surviving glyphosate application and sampled for DNA analyses had the point mutation P106A. The biotype 19-1 can be confirmed as glyphosate-resistant, representing the first glyphosate-resistant population of E. indica in Europe.

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Kumar, Vipan, Prashant Jha, Darci Giacomini, Eric P. Westra, and Philip Westra. "Molecular Basis of Evolved Resistance to Glyphosate and Acetolactate Synthase-Inhibitor Herbicides in Kochia (Kochia scoparia) Accessions from Montana." Weed Science 63, no. 4 (December 2015): 758–69. http://dx.doi.org/10.1614/ws-d-15-00021.1.

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The rapid evolution and spread of glyphosate-resistant (GR) kochia in the Northern Great Plains is an increasing threat to GR cropping systems and conservation tillage practices common in this region. GR kochia accessions with 4.6- to 11-fold levels of resistance to glyphosate have recently been reported in Montana. Those GR kochia accessions were also suspected to be resistant to acetolactate synthase (ALS) inhibitors, i.e., multiple herbicide-resistant (MHR) kochia. In this research, the level of resistance to the ALS-inhibitor herbicides (sulfonylureas) and the molecular mechanisms conferring resistance to glyphosate and ALS-inhibitor herbicides in MHR kochia was investigated. On the basis of whole-plant dose–response assays, MHR kochia accessions (GIL01, JOP01, and CHES01) were 9.3- to 30-fold more resistant to premixed thifensulfuron methyl + tribenuron methyl + metsulfuron methyl than the susceptible (SUS) accession. In an in vivo leaf-disk shikimate assay, MHR plants accumulated less shikimate than the SUS plants at a discriminate dose of 100 μM glyphosate. Sequencing of the conserved region ofEPSPSrevealed no target-site mutation at Thr102or Pro106residue. MHR kochia accessions had increased relativeEPSPSgene copies (~ 4 to 10) compared with the SUS accession (single copy). Furthermore, MHR kochia accumulated higher EPSPS protein compared with the SUS plants. Resistance to the ALS-inhibitor herbicides was conferred by Pro197amino acid substitution (proline to glutamine).EPSPSgene amplification and a single target-site mutation at Pro197inALSgene confer resistance to glyphosate and ALS-inhibitor herbicides, respectively, in MHR kochia accessions from Montana. This is the first confirmation of occurrence of MHR kochia in Montana.

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Franci, Julop, Kok Wai Lam, Tse Seng Chuah, and Thye San Cha. "Genetic diversity and in silico evidence of target-site mutation in the EPSPS gene in endowing glyphosate resistance in Eleusine indica (L.) from Malaysia." Pesticide Biochemistry and Physiology 165 (May 2020): 104556. http://dx.doi.org/10.1016/j.pestbp.2020.104556.

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Jasieniuk, Marie, Riaz Ahmad, Anna M. Sherwood, Jeffrey L. Firestone, Alejandro Perez-Jones, W. Thomas Lanini, Carol Mallory-Smith, and Zachary Stednick. "Glyphosate-Resistant Italian Ryegrass (Lolium multiflorum) in California: Distribution, Response to Glyphosate, and Molecular Evidence for an Altered Target Enzyme." Weed Science 56, no. 4 (August 2008): 496–502. http://dx.doi.org/10.1614/ws-08-020.1.

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Selection by herbicides has resulted in widespread evolution of herbicide resistance in agricultural weeds. In California, resistance to glyphosate was first confirmed in rigid ryegrass in 1998. Objectives of this study were to determine the current distribution and level of glyphosate resistance in Italian ryegrass, and to assess whether resistance could be due to an altered target site. Seeds were sampled from 118 populations and seedlings were treated with glyphosate at 866 g ae ha−1. Percentage of survivors ranged from 5 to 95% in 54 populations. All plants from 64 populations died. One susceptible (S) population, four putatively resistant (R) populations, and one S accession from Oregon were used for pot dose–response experiments, shikimic acid analyses, and DNA sequencing. Seedlings were treated with glyphosate at eight rates, ranging from 108 to 13,856 g ae ha−1. Shoot biomass was evaluated 3 wk after treatment and fit to a log-logistic regression equation. On the basis of GR50(herbicide rate required to reduce growth by 50%) values, seedlings from putatively R populations were roughly two to 15 times more resistant to glyphosate than S plants. Shikimic acid accumulation was similar in all plants before glyphosate treatment, but at 4 and 7 DAT, S plants from California and Oregon accumulated approximately two and three times more shikimic acid, respectively, than R plants. Sequencing of a cDNA fragment of the EPSPS coding region revealed two different codons, both of which encode proline at amino acid position 106 in S individuals. In contrast, all R plants sequenced exhibited missense mutations at site 106. Plants from one population revealed a mutation resulting in a proline to serine substitution. Plants from three R populations exhibited a mutation corresponding to replacement of proline with alanine. Our results indicate that glyphosate resistance is widespread in Italian ryegrass populations of California, and that resistance is likely due to an altered target enzyme.

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Han, Heping, Qin Yu, Michael J. Widderick, and Stephen B. Powles. "Target-site EPSPS Pro-106 mutations: sufficient to endow glyphosate resistance in polyploidEchinochloa colona?" Pest Management Science 72, no. 2 (June 1, 2015): 264–71. http://dx.doi.org/10.1002/ps.4038.

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Fonseca, Emily C. M., Kauê S. da Costa, Jerônimo Lameira, Cláudio Nahum Alves, and Anderson H. Lima. "Investigation of the target-site resistance of EPSP synthase mutants P106T and T102I/P106S against glyphosate." RSC Advances 10, no. 72 (2020): 44352–60. http://dx.doi.org/10.1039/d0ra09061a.

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Alarcón-Reverte, Rocío, Alejandro García, Susan B. Watson, Ibrahim Abdallah, Sebastián Sabaté, María J. Hernández, Franck E. Dayan, and Albert J. Fischer. "Concerted action of target-site mutations and high EPSPS activity in glyphosate-resistant junglerice (Echinochloa colona) from California." Pest Management Science 71, no. 7 (September 5, 2014): 996–1007. http://dx.doi.org/10.1002/ps.3878.

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Powles, Stephen B., and Christopher Preston. "Evolved Glyphosate Resistance in Plants: Biochemical and Genetic Basis of Resistance." Weed Technology 20, no. 2 (June 2006): 282–89. http://dx.doi.org/10.1614/wt-04-142r.1.

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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.

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González-Torralva, Fidel, Javier Gil-Humanes, Francisco Barro, José A. Domínguez-Valenzuela, and Rafael De Prado. "First evidence for a target site mutation in the EPSPS2 gene in glyphosate-resistant Sumatran fleabane from citrus orchards." Agronomy for Sustainable Development 34, no. 2 (July 4, 2013): 553–60. http://dx.doi.org/10.1007/s13593-013-0163-8.

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Preston, Christopher, Angela M. Wakelin, Fleur C. Dolman, Yazid Bostamam, and Peter Boutsalis. "A Decade of Glyphosate-ResistantLoliumaround the World: Mechanisms, Genes, Fitness, and Agronomic Management." Weed Science 57, no. 4 (August 2009): 435–41. http://dx.doi.org/10.1614/ws-08-181.1.

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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.

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Torra, Joel, José M. Montull, Isabel M. Calha, María D. Osuna, Joao Portugal, and Rafael de Prado. "Current Status of Herbicide Resistance in the Iberian Peninsula: Future Trends and Challenges." Agronomy 12, no. 4 (April 13, 2022): 929. http://dx.doi.org/10.3390/agronomy12040929.

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The evolution of herbicide resistance in weeds has emerged as one of the most serious threats to sustainable food production systems, which necessitates the evaluation of herbicides to determine their efficacy. The first herbicide resistance case in the Iberian Peninsula was reported about 50 years ago, wherein Panicum dichotomiflorum was found to be resistant (R) to atrazine in Spanish maize fields. Since then, herbicide resistance has evolved in 33 weed species, representing a total of 77 single-herbicide-resistance cases in this geographic area: 66 in Spain and 11 in Portugal. Changes in agricultural practices, namely the adoption of non-tillage systems and the increased use of herbicides, led to the selection of weed biotypes resistant to a wide range of herbicides. Nowadays the most important crops in Spain and Portugal (maize, winter cereals, rice, citrus, fruits, and olive orchards) are affected, with biotypes resistant to several mechanisms of action (MoAs), namely: ALS inhibitors (20 species), ACCase inhibitors (8 species), PS II inhibitors (18 species), and synthetic auxin herbicides (3 species). More recently, the fast increase in cases of resistance to the EPSPS-inhibiting herbicide glyphosate has been remarkable, with 11 species already having evolved resistance in the last 10 years in the Iberian Peninsula. The diversity of resistance mechanisms, both target-site and non-target-site, are responsible for the resistance to different MoAs, involving point mutations in the target site and enhanced rates of herbicide detoxification, respectively. More serious are the 13 cases reported with multiple-herbicide resistance, with three cases of resistance to three–four MoAs, and one case of resistance to five MoAs. Future research perspectives should further study the relationship between management strategies and the occurrence of TSR and NTSR resistance, to improve their design, develop monitoring and diagnostic tools for herbicide resistance, and deepen the study of NTSR resistance.

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Singh, Shilpa, Vijay Singh, Amy Lawton-Rauh, Muthukumar V. Bagavathiannan, and Nilda Roma-Burgos. "EPSPSGene Amplification Primarily Confers Glyphosate Resistance among Arkansas Palmer amaranth (Amaranthus palmeri) Populations." Weed Science 66, no. 3 (January 26, 2018): 293–300. http://dx.doi.org/10.1017/wsc.2017.83.

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AbstractResearch was conducted to determine whether resistance to glyphosate among Palmer amaranth (Amaranthus palmeriS. Watson) populations within the U.S. state of Arkansas was due solely to increasedEPSPSgene copy number and whether gene copy number is correlated with resistance level to glyphosate. One hundred and fifteenA. palmeriaccessions were treated with 840 g ae ha−1glyphosate. Twenty of these accessions, selected to represent a broad range of responses to glyphosate, underwent further testing. Seven of the accessions were controlled with this dose; the rest were resistant. The effective dose to cause 50% injury (ED50) for susceptible accessions ranged from 28 to 207 g ha−1. The glyphosate-resistant (GR) accessions had ED50values ranging from 494 to 1,355 g ha−1, a 3- to 48-fold resistance level compared with the susceptible standard (SS). The 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene relative copy number was determined for 20 accessions, 4 plants accession−1. Resistant plants from five GR accessions (38% of resistant plants tested) did not have increasedEPSPSgene copies. Resistant plants from the remaining eight GR accessions (62% of resistant plants tested) had 19 to 224 moreEPSPSgene copies than the SS. Among the accessions tested, injury declined 4% with every additionalEPSPScopy. ED50values were directly correlated withEPSPScopy number. The highly resistant accession MIS11-B had an ED50of 1,355 g ha−1and 150 gene copies. Partial sequences ofEPSPSfrom GR accessions withoutEPSPSamplification did not contain any of the known resistance-conferring mutations. Nearly 40% of GR accessions putatively harbor non–target site resistance mechanisms. Therefore, elevatedEPSPSgene copy number is associated with glyphosate resistance amongA. palmerifrom Arkansas.

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Liu, Chun, Lucy V. Jackson, Sarah-Jane Hutchings, Daniel Tuesca, Raul Moreno, Eddie Mcindoe, and Shiv S. Kaundun. "A holistic approach in herbicide resistance research and management: from resistance detection to sustainable weed control." Scientific Reports 10, no. 1 (November 26, 2020). http://dx.doi.org/10.1038/s41598-020-77649-z.

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AbstractAgricultural weeds can adapt rapidly to human activities as exemplified by the evolution of resistance to herbicides. Despite its multi-faceted nature, herbicide resistance has rarely been researched in a holistic manner. A novel approach combining timely resistance confirmation, investigation of resistance mechanisms, alternative control solutions and population modelling was adopted for the sustainable management of the Amaranthus palmeri weed in soybean production systems in Argentina. Here, we show that resistance to glyphosate in the studied population from Cordoba province was mainly due to a P106S target-site mutation in the 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) gene, with minor contributions from EPSPS gene duplication/overexpression. Alternative herbicides, such as fomesafen, effectively controlled the glyphosate-resistant plants. Model simulations revealed the tendency of a solo herbicidal input to primarily select for a single resistance mechanism and suggested that residual herbicides, alongside chemical diversity, were important for the sustainable use of these herbicides. We also discuss the value of an interdisciplinary approach for improved understanding of evolving weeds.

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Beres, Zachery T., Laura A. Giese, David M. Mackey, Micheal D. K. Owen, Eric R. Page, and Allison A. Snow. "Target-site EPSPS Pro-106-Ser mutation in Conyza canadensis biotypes with extreme resistance to glyphosate in Ohio and Iowa, USA." Scientific Reports 10, no. 1 (May 5, 2020). http://dx.doi.org/10.1038/s41598-020-64458-7.

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García, Maria J., Candelario Palma-Bautista, José G. Vazquez-Garcia, Antonia M. Rojano-Delgado, María D. Osuna, Joel Torra, and Rafael De Prado. "Multiple mutations in the EPSPS and ALS genes of Amaranthus hybridus underlie resistance to glyphosate and ALS inhibitors." Scientific Reports 10, no. 1 (October 19, 2020). http://dx.doi.org/10.1038/s41598-020-74430-0.

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Abstract Amaranthus hybridus is one of the main weed species in Córdoba, Argentina. Until recently, this weed was effectively controlled with recurrent use of glyphosate. However, a population exhibiting multiple resistance (MR2) to glyphosate and imazamox appeared in a glyphosate resistant (GR) soybean field, with levels of resistance up to 93 and 38-fold higher to glyphosate and imazamox, respectively compared to the susceptible (S) population. In addition to imidazolinones, MR2 plants showed high resistance levels to sulfonylamino-carbonyl (thio) benzoates and moderate resistance to sulfonylureas and triazolopyrimidines. Multiple amino acid substitutions were found in both target genes, acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), responsible for conferring high herbicides resistance levels in this A. hybridus population. In the case of EPSPS, the triple amino acid substitution TAP-IVS was found. In addition, MR2 plants also showed increased EPSPS gene expression compared to susceptible plants. A Ser653Asn substitution was found in the ALS sequence of MR2, explaining the pattern of cross-resistance to the ALS-inhibitor herbicide families found at the ALS enzyme activity level. No other mutations were found in other conserved domains of the ALS gene. This is the first report worldwide of the target site resistance mechanisms to glyphosate and ALS inhibitors in multiple herbicide resistance Amaranthus hybridus.

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Yang, So Hee, Euyeon Kim, Hyosun Park, and Yeonjong Koo. "Selection of the high efficient sgRNA for CRISPR-Cas9 to edit herbicide related genes, PDS, ALS, and EPSPS in tomato." Applied Biological Chemistry 65, no. 1 (February 9, 2022). http://dx.doi.org/10.1186/s13765-022-00679-w.

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AbstractHerbicide resistance is one of the main crop traits that improve farming methods and crop productivity. CRISPR-Cas9 can be applied to the development of herbicide-resistant crops based on a target site resistance mechanism, by editing genes encoding herbicide binding proteins. The sgRNAs capable of editing the target genes of herbicides, pds (phytoene desaturase), ALS (acetolactate synthase), and EPSPS (5-Enolpyruvylshikimate-3-phosphate synthase), were designed to use with the CRISPR-Cas9 system in tomato (Solanum lycopersicum cv. Micro-Tom). The efficiency of the sgRNAs was tested using Agrobacterium mediated transient expression in the tomato cotyledons. One sgRNA designed for editing the target site of PDS had no significant editing efficiency. However, three different sgRNAs designed for editing the target site of ALS had significant efficiency, and one of them, ALS2-P sgRNA, showed over 0.8% average efficiency in the cotyledon genome. The maximum efficiency of ALS2-P sgRNA was around 1.3%. An sgRNA for editing the target site of EPSPS had around 0.4% editing efficiency on average. The sgRNA efficiency testing provided confidence that editing of the target sites could be achieved in the transformation process. We confirmed that 19 independent transgenic tomatoes were successfully edited by ALS2_P or ALS1_W sgRNAs and two of them had three base deletion mutations, which are expected to have altered herbicide resistance. In this study, we demonstrated the usefulness of performing an sgRNA efficiency test before crop transformation, and confirmed that the CRISPR-Cas9 system is a valuable tool for breeding herbicide-resistant crops.

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Li, Zhiling, Xiangju Li, Hailan Cui, Guodong Zhao, Dan Zhai, and Jingchao Chen. "Vegetative and Fecundity Fitness Benefit Found in a Glyphosate-Resistant Eleusine indica Population Caused by 5-Enolpyruvylshikimate-3-Phosphate Synthase Overexpression." Frontiers in Plant Science 12 (November 19, 2021). http://dx.doi.org/10.3389/fpls.2021.776990.

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Fitness is an important trait in weed species that have developed herbicide resistance, including resistance to the popular herbicide glyphosate. Fitness cost is commonly found in weeds with glyphosate resistance, which is caused by target-site mutations. In this study, the vegetative and fecundity fitness traits in a glyphosate-resistant (GR) Eleusine indica population caused by 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) overexpression were investigated under glyphosate-free conditions. The results showed that the resistance index of the population resistant (R) to glyphosate compared with that of the population susceptible (WT) to it was approximately 4.0. Furthermore, EPSPS expression level in the R plants was 20.1–82.7 times higher than that in the WT plants. The dry weight of the R population was significantly higher than that of the WT population at the later growth stage after planting; a similar trend was observed for leaf area. In addition, seed production in the R population was 1.4 times higher than that in the WT population. The R and WT populations showed similar maximum germination rates and T50 values. UPLC-MS/MS was performed for the metabolic extracts prepared from the leaves of R and WT populations to address changes in the metabolome. A total of 121 differential metabolites were identified between R and WT individuals. The levels of 6-hydroxy-1H-indole-3-acetamide and indole acetaldehyde, which are associated with auxin synthesis, were significantly higher in plants of the R population than in those of the WT population. However, some secondary metabolite levels were slightly lower in the R population than in the WT population. To conclude, in this study, vegetative and fecundity fitness benefits were found in the GR E. indica population. The results of metabolome analysis indicate that the increase in 6-hydroxy-1H-indole-3-acetamide and indole acetaldehyde levels may be the result of fitness benefit. Further studies should be conducted to confirm the functions of these metabolites.

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Journal articles on the topic 'EPSPS target-site mutation'

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