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Background: Echinochloa crus-galli is the most troublesome and widespread weed of most rice-growing regions of the world. Cyhalofop-butyl, a herbicide within the acetyl-CoA carboxylase (ACCase) chemical group, has been extensively used to control barnyardgrass in rice. The repeated exposure to cyhalofop-butyl has led to resistance evolution in E. crus-galli populations., Results: In this study, we identified a population of E. crus-galli (R-HN) in a rice field in Hunan, China, that developed resistance to cyhalofop-butyl at 4.49-fold the recommended field dose. No known target mutation was detected in the ACCase gene of the R-HN population by ACCase sequencing compared to sensitive populations. Both cytochrome P450 (CYP450) and glutathione S-transferase (GST) inhibitors could not significantly reverse the resistance to cyhalofop-butyl. The nontarget-site resistance (NTSR) mechanism was investigated by transcriptome sequencing. Validation of the screened candidate genes by quantitative real-time (qRT)-PCR revealed that six glycosyltransferases (GTs) and four ATP-binding cassette (ABC) transporter genes were consistently upregulated in the R-HN population. Five GTs and one ABC transporter genes were constitutively upregulated after cyhalofop-butyl treatment in the R-HN population. Molecular docking results showed that the significant binding energy of GT79, GT75L6 and GT74E among all candidate genes., Conclusion: Thus, the GT genes appear to be directly implicated in NTSR to cyhalofop-butyl in the R-HN populations through metabolic enhancement, but their functional characterization needs to be studied. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

BACKGROUND: Barnyardgrass (Echinochloa crus‐galli (L.) P. Beauv) has evolved resistance to the acetolactate synthase (ALS) inhibitor penoxsulam which is used to control weeds in rice fields in China. The present study is conducted to identify the target‐site resistance (TSR) mechanisms conferring resistance in a penoxsulam‐resistant population. RESULTS: The ALS sensitivity in vitro of the resistant population was sixfold lower to penoxsulam than that of the sensitive population. ALS sequencing revealed that no known mutation conferring ALS herbicide resistance was detected. However, a novel mutation Phe‐206‐Leu was identified in the ALS gene. Additionally, ALS gene expression level of the resistant population was lower than that of the sensitive population. Therefore, the penoxsulam resistance was not due to the overexpression of ALS gene. Molecular docking revealed that this mutation may change the interaction of the penoxsulam‐ALS binding and weaken its mutual affinity by approximately 10%. Arabidopsis thaliana transformed with mutant ALS had fourfold greater resistance to penoxsulam and varied cross‐resistance to other ALS herbicides than those transformed with sensitive ALS. Mutant and sensitive ALS proteins expressed by the baculovirus system exhibited different in vitro penoxsulam sensitivity levels. Mutant ALS had eightfold lower sensitivity to penoxsulam than sensitive ALS. CONCLUSION: This report provides clear evidence that the ALS mutation at position 206 (Phe‐206‐Leu) confers penoxsulam resistance in barnyardgrass. Phe‐206 was confirmed to be the ninth amino acid residue related to ALS herbicide resistance in weeds. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Echinochloa crus-galli is a major weed in rice fields in China, and quinclorac has been long used for its control. Over-reliance of quinclorac has resulted in quinclorac resistance in E. crus-galli. Two resistant (R) E. crus-galli populations from Hunan, China were confirmed to be at least 78-fold more resistant to quinclorac than the susceptible (S) population. No difference in foliar uptake of 14C-labelled quinclorac was detected between the R and S plants. However, a higher level of 14C translocation and a lower level of quinclorac metabolism were found in the R plants. Basal and induced expression levels of β-cyanoalanine synthase (β-CAS) gene and β-CAS activity were not significantly different between the R and S plants. However, the induction expression of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO1) gene by quinclorac treatment was evident in the S plants but not in the R plants. Quinclorac resistance in the two resistant E. crus-galli populations was not likely to be related to foliar uptake, translocation or metabolism of quinclorac, nor to cyanide detoxification via β-CAS. Thus, target-site based quinclorac signal reception and transduction and regulation of the ethylene synthesis pathway should be the focus for further research. [ABSTRACT FROM AUTHOR]

Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.), one of the worst weeds in paddy fields in China, has been frequently reported evolving resistance to acetyl-CoA carboxylase (ACCase) inhibiting herbicides. However, in the previous research, more attention was paid to target-site resistance (TSR) mechanisms, the non-target-site resistance (NTSR) mechanisms have not been well-established. In this study, the potential mechanism of resistance in a metamifop-resistant E. crus-galli collected from Kunshan city, Jiangsu Province, China was investigated. Dose-response assays showed that the phenotypic resistant population (JS-R) has evolved 4.3-fold resistance to metamifop compared with the phenotypic susceptible population (YN-S). The ACCase CT gene sequencing and relative ACCase gene expression levels studies showed that no mutations were detected in the ACCase CT gene in both YN-S and JS-R, and there was no significant difference in the relative ACCase gene expression between YN-S and JS-R. After the pre-processing of glutathione-S-transferase (GSTs) inhibitor NBD-Cl, the resistance level of JS-R to metamifop was reversed 18.73%. Furthermore, the GSTs activity of JS-R plants was significantly enhanced compared to that of YN-S plants. UPLC-MS/MS revealed that JS-R plants had faster metabolic rates to metamifop than YN-S plants. Meanwhile, the JS-R popultion exhibited resistant to cyhalofop-butyl and penoxsulam. In summary, this study presented a novel discovery regarding the global emergence of metabolic resistance to metamifop in E. crus-galli. The low-level resistance observed in the JS-R population was not found to be related to TSR but rather appeared to be primarily associated with the overexpression of genes in the GSTs metabolic enzyme superfamily. [Display omitted] • Echinochloa crus-galli evolved resisitant to metamifop in China. • The resistance of Echinochloa crus-galli to metamifop was not related to target-site resistance. • We provide evidence of the metabolic resistance to metamifop mediated by GSTs in Echinochloa crus-galli in China. • Echinochloa crus-galli metamifop-resistant population also evolved resisitant to cyhalofop-butyl and penoxsulam. [ABSTRACT FROM AUTHOR]

Barnyardgrass ( Echinochloa crus-galli) proliferation seriously threatens rice production worldwide. Whole-plant bioassays were conducted in order to test the sensitivity to penoxsulam of 52 barnyardgrass populations and the resistance of six penoxsulam-resistant populations to 12 other herbicides that are commonly used in rice fields. Among the 48 populations that had escaped penoxsulam control in the rice fields, 8.3% showed a very high level of resistance, 58.3% showed a high level of resistance and 10.4% showed a moderate level of resistance. Multiple resistance was confirmed in all six penoxsulam-resistant populations that were tested further. They exhibited at least a moderate level of resistance; that is, to 6-10 of the total of 13 herbicides that was tested. Most of the six penoxsulam-resistant populations showed at least a moderate level of resistance to bispyribac-sodium, quinclorac, metamifop, cyhalofop-butyl and oxadiazon, three populations held at least a moderate level of resistance to oxyfluorfen and pretilachlor, two populations also held at least a moderate level of resistance to pyrazosulfuron-ethyl, pyribenzoxim and fenoxaprop-P-ethyl, but the resistance indices of the six populations to pendimethalin were all low. This study has confirmed resistance to pretilachlor and oxadiazon in weeds for the first time. [ABSTRACT FROM AUTHOR]

A quizalofop-resistant Echinochloa crus-galli biotype (RR) was collected from Geqiushan Farm in Heilongjiang Province. Gramineae acetyl-CoA carboxylase (ACCase) in plastid is the target site of quizalofop. Two full-length cDNAs of the plastid ACCase from RR and sensitive Echinochloa crusgalli (SS) were cloned. Plastid ACCase cDNA from RR encodes a protein of 2316 amino acids with an estimated isoelectric point of 5.97 and a calculated molecular mass of 256 kD. The two sequences were compared with their homologs from other plants and the deduced proteins were analyzed to identify plastid ACCase. It was found that the amino acid at position 1781 (standardized to Alopecurus myosuroides) was Leu in RR, while Ile in SS and other cereal plastid ACCases. It was suspected that the change of Ile to Leu residue related to the resistance to quizalofop of RR. [ABSTRACT FROM AUTHOR]