Acetolactate Synthase Overexpression in Mesosulfuron-Methyl-Resistant Shortawn Foxtail ( Alopecurus aequalis Sobol.): Reference Gene Selection and Herbicide Target Gene Expression Analysis

Metabolism-Based Nontarget-Site Mechanism Is the Main Cause of a Four-Way Resistance in Shortawn Foxtail (Alopecurus aequalis Sobol.)

Alopecurus aequalis Sobol. is a predominant grass weed in Chinese winter wheat fields, posing a substantial threat to crop production owing to its escalating herbicide resistance. This study documented the initial instance of an A. aequalis population (AHFT-3) manifesting resistance to multiple herbicides targeting four distinct sites: acetyl-CoA carboxylase (ACCase), acetolactate synthase, photosystem II, and 1-deoxy-d-xylulose-5-phosphate synthase. AHFT-3 carried an Asp-to-Gly mutation at codon 2078 of ACCase, with no mutations in the remaining three herbicide target genes, and exhibited no overexpression of any target gene. Compared with the susceptible population AHFY-3, AHFT-3 metabolized mesosulfuron-methyl, isoproturon, and bixlozone faster. The inhibition and comparison of herbicide-detoxifying enzyme activities indicated the participation of cytochrome P450s in the resistance to all four herbicides, with glutathione S-transferases specifically linked to mesosulfuron-methyl. Three CYP72As and a Tau class glutathione S-transferase, markedly upregulated in resistant plants, potentially played pivotal roles in the multiple-herbicide-resistance phenotype.

Target-site and non-target-site resistance mechanisms confer mesosulfuron-methyl resistance in Alopecurus aequalis

BACKGROUND

Shortawn foxtail (Alopecurus aequalis Sobol.) is a noxious weed in China. The resistance of A. aequalis developed rapidly due to the long-term application of acetolactate synthase (ALS)-inhibiting herbicides. Here, a suspected mesosulfuron-methyl-resistant A. aequalis population, Aa-R, was collected from a wheat field in China.

RESULTS

A dose‒response test showed that the Aa-R population has evolved a high level of resistance to mesosulfuron-methyl, and its growth was suppressed by imazamox, pyroxsulam and bispyribac-sodium. ALS gene sequence analysis revealed that a known resistance-related mutation (Pro-197-Thr) was present in the Aa-R population. Moreover, ALS gene overexpression was detected in the Aa-R population. The mesosulfuron-methyl resistance could be reversed by cytochrome P450 monooxygenase (CYP450) and glutathione S-transferase (GST) inhibitors. In addition, enhanced metabolism of mesosulfuron-methyl was detected in the Aa-R population compared with the susceptible population. NADPH-cytochrome P450 reductase and GST activities were strongly inducible in the Aa-R population. One CYP450 gene, CYP74A2, and one GST gene, GST4, were constitutively upregulated in the Aa-R population. Molecular docking results showed the binding affinity of CYP74A2 and GST4 for the tested ALS-inhibiting herbicides, respectively.

CONCLUSION

This study confirmed that target-site resistance and non-target-site resistance involving CYP450 and GST were the main mechanisms involved in resistance in the mesosulfuron-methyl-resistant A. aequalis population.

Cytochrome P450s-Involved Enhanced Metabolism Contributes to the High Level of Nicosulfuron Resistance in Digitaria sanguinalis from China

Large crabgrass (Digitaria sanguinalis (L.) Scop.) is one of the major malignant grass weeds in Chinese maize (Zea mays L.) fields, and it has recently developed resistance to the acetolactate synthase (ALS)-inhibiting herbicide nicosulfuron. This study focused on a suspected nicosulfuron-resistant (R) population (LJ-01) of D. sanguinalis, collected from Lujiang County in Anhui Province, China, to explore the resistance level and potential resistance mechanism. Whole-plant dose-response testing confirmed that the LJ-01 population evolved a high level of resistance to nicosulfuron (11.5-fold) compared to the susceptible (S) population, DY-02. The ALS gene sequencing and relative expression assay of the R plants indicated that target gene mutation and overexpression were not responsible for the resistance phenotype. However, pretreatment with malathion, a known cytochrome P450 monooxygenase (P450) inhibitor, alleviated the resistance of the R population to nicosulfuron by approximately 36%. High-performance liquid chromatography (HPLC) analysis revealed that the R plants metabolized nicosulfuron faster than the S plants. Moreover, cross-resistance testing suggested that the R population exhibited low levels of resistance to thifensulfuron-methyl and pyrazosulfuron-ethyl, but it remained susceptible to rimsulfuron. Multiple resistance patterns showed that the R population evolved low resistance to the photosystem inhibitors bromoxynil octanoate and atrazine and sensitivity to the acetyl-CoA carboxylase (ACCase) inhibitor cyhalofop-butyl and the 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors tembotrione, mesotrione, and topramezone. This study reports, for the first time, the simultaneous resistance to ALS and different photosystem inhibitors in D. sanguinalis. The nicosulfuron resistance observed in the R population could primarily be attributed to an enhanced metabolism involving P450 enzymes.

Investigation of resistance mechanisms to fomesafen in Ipomoea nil from China

Recently, the herbicide fomesafen has frequently failed to control the troublesome weed Ipomoea nil in soybean fields in Liaoning Province, China. Hence, we collected 10 suspected resistant populations and evaluated their sensitivity to fomesafen. The results revealed various degrees of Ipomoea nil resistance to fomesafen, with a resistance index of 2.88 to 22.43; the highest value occurred in the LN3 population. Therefore, the mechanisms of the resistance in LN3 to fomesafen were explored. After fomesafen treatment, the expression levels of InPPX1 and InPPX2 genes were 4.19- and 9.29-fold higher, respectively, in LN3 than those in the susceptible (LN1) population. However, mutations and copy number variations were not detected between the two populations. Additionally, malathion pretreatment reduced the dose necessary to halve the growth rate of LN3 by 58%. Liquid chromatography with tandem mass spectrometry demonstrated that metabolism of fomesafen was significantly suppressed by malathion. Moreover, LN3 displayed increased reactive oxygen species scavenging capacity, which was represented by higher superoxide dismutase and peroxidase activities after fomesafen application than those in LN1. An orthogonal partial least squares-discriminant analysis revealed that the high resistance in LN3 could be attributed mainly to enhanced metabolism. Fortunately, the fomesafen-resistant I. nil remained sensitive to 2,4-D-ethylhexylester and bentazon, providing methods for its control.

Selection and verification of reliable internal reference genes in stem development of herbaceous peony (Paeonia lactiflora Pall.)

Herbaceous peony (Paeonia lactiflora Pall.) has emerged in the cut flower market due to its beautiful appearance. The bending flower stems caused by a lack of mechanical strength is the main problem restricting the development of the cut P. lactiflora industry. So it is of great worth to reveal the basis of stem development changes in P. lactiflora to improve its cut flower quality. Quantitative research on gene expression characteristics can provide clues for understanding their biological functions, and the screening of relatively stable expression genes is a prerequisite for the quantitative study of gene expression characteristics. Thus, it is necessary to find appropriate genes during stem development so as to analyze the qRT‒PCR results. In this study, 10 genes were screened, and these genes expressed stably in stems of different stem strengths at three different developmental stages. Then, their expressions were evaluated by RefFinder, BestKeeper, NormFinder, and GeNorm programs. The results demonstrated that γ-tubulin (γ-TUB) was the most suitable gene, followed by α-tubulin (α-TUB) and β-D-glucosidase (β-GUS), whereas histone H3 (His) was the least suitable gene. Besides, the temporal and spatial expression characteristics of PlCOMT1, the key gene concerned with the synthesis of cell wall fillers in P. lactiflora, were also used to evaluate the suitability of genes. Consequently, γ-TUB and α-TUB are the two best combinations during stem development, and their combination can be used for the stem development of P. lactiflora. These findings will provide a reference for the selection of genes related to stem development and the study of molecular mechanisms related to stem development in P. lactiflora.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01325-5.

Mutation at the 197 site and P450-mediated metabolic resistance are involved in bensulfuron-methyl resistance in Sagittaria trifolia

Sagittaria trifolia control is threatened by the emergence of resistance to acetolactate synthase (ALS)-inhibiting herbicides. Hence, we systematically uncovered the molecular mechanism of resistance to the main herbicide (bensulfuron-methyl) in Liaoning Province from target-site and non-target-site resistance perspectives. The suspected resistant population (TR-1) exhibited high-level resistance. A new amino acid substitution (Pro-197-Ala) in resistant Sagittaria trifolia for ALS was detected, and the molecular docking results showed that the spatial structure of ALS changed significantly after the substitution, manifested by an increase in the number of contacted amino acid residues and the disappearance of hydrogen bonds. Dose-response test of transgenic Arabidopsis thaliana further demonstrated that the Pro-197-Ala substitution conferred bensulfuron-methyl resistance. The assays found that the sensitivity of the ALS enzyme in TR-1 to this herbicide was decreased in vitro; and this population had developed resistance to other types of ALS-inhibiting herbicides. Furthermore, the resistance of TR-1 to bensulfuron-methyl was significantly alleviated after co-treatment with a P450-inhibitor (malathion). TR-1 metabolized bensulfuron-methyl significantly faster than sensitive population (TS-1) did, but this gap was narrowed after malathion treatment. Overall, the resistance of Sagittaria trifolia to bensulfuron-methyl was derived from the mutation of the target-site gene and the enhancement of the P450s-mediated detoxification metabolism.

Occurrence and mechanism of target-site resistance to bensulfuron-methyl in Monochoria korsakowii from China

Monochoria korsakowii is an increasingly significant threat to rice production across China, particularly in Liaoning province. Few studies have reported herbicide resistance in M. korsakowii, and resistance status and mechanisms are poorly understood. Here, thirty field populations of M. korsakowii were collected from 11 rice-growing regions of Liaoning, and 97% of populations had evolved resistance to bensulfuron-methyl (BM), with majority (24 of 28) showing high resistance levels (RI > 10). The first in-depth analysis of molecular features of AHAS1 and AHAS2 in BM-resistant populations showed that four Pro197 mutations (Pro197 to His, Ala, Leu or Ser) in AHAS1 and one mutation (Pro197Ser) in AHAS2 were identified. Notably, novel double Pro197Ser mutations co-occurred in both AHAS1 and AHAS2 in the most resistant line LN-20. Furthermore, resistant mutants were used to investigate the effect of Pro197 mutations on AHAS functionality, binding modes, gene expression and cross-resistance in M. korsakowii. All the detected Pro197 mutations considerably reduced in vitro AHAS sensitivity to BM by weakening hydrogen bonds and hydrophobic interactions in the predicted BM-AHAS complexes, especially the double Pro197Ser mutations. This novel resistance mutation combination slightly impacted the extractable AHAS activity, and increased the affinity and catalytic rate of pyruvate. Also, the AHAS expression level was significantly up-regulated. Moreover, all mutations provided resistance only to other sulfonylureas herbicides but not triazolopyrimidine or pyrimidinyl-benzoates herbicides. In conclusion, bensulfuron-methyl resistance in M. korsakowii was grim in Liaoning, China, and amino acid mutations on AHAS isozymes were the primary resistance mechanism. Double Pro197Ser mutations in both AHAS1 and AHAS2 confer higher herbicide resistance than single mutations in AHAS1. Thus, this work deepens our understanding of resistance status and mechanisms of M. korsakowii.

Comparative analysis of fungal communities between herbicide-resistant and -susceptible Alopecurus aequalis

Introduction

Alopecurus aequalis is a grass species invading Chinese canola and wheat fields. An A. aequalis KMN-R population surviving mesosulfuron-methyl treatment with recommended rates was acquired from wheatland. Here, we aimed to confirm the resistance profiles of KMN-R to acetolactate synthetase (ALS) inhibiting herbicides and explore the possible resistance mechanisms to mesosulfuron-methyl in this weed population.

Methods

The dose-response tests performed in our study were used to test the toxicity of A. aequalis to ALS-inhibiting herbicides. Sanger sequencing was used to analyze the ALS gene of mesosulfuron-methyl -resistant and -susceptible A. aequalis. RNA sequencing analysis was used to find candidate genes that may confer metabolic resistance to the mesosulfuron-methyl in resistant A. aequalis population. Mesosulfuron-methyl -resistant and -susceptible A. aequalis populations fungal composition was measured via Illumina MiSeq Sequencing.

Results

Dose-response results indicated that KMN-R population evolved resistance to mesosulfuron-methyl and other tested ALS-inhibiting herbicides. Known resistance-conferring Trp-574-Leu gene mutation in A. aequalis ALS was detected in the KMN-R population. Pretreatment with 4-chloro-7-nitrobenzoxadiazole reversed mesosulfuron-methyl resistance in KMN-R. Glutathione S-transferases (GST) gene GSTZ2 and GSTT3 were highly expressed in KMN-R population. In addition, we evaluated the alpha diversity in A. aequalis, centering on OTU abundance, equality, and multiplicity, and found that the fungal community composition had more unexplained variance between KMN-R and KMN-S A. aequalis. We also observed higher abundances of specific fungi in KMN-R A. aequalis.

Discussion

The results proved that resistance to mesosulfuron-methyl in A. aequalis KMN-R population is probably caused by target site- and non-target site-based relating GST and provided the basis for further research between fungal interaction and herbicide resistance.

First Report of the Molecular Mechanism of Resistance to Tribenuron-Methyl in Silene conoidea L

Silene conoidea L. is an annual troublesome broadleaf weed in winter wheat fields in China. In recent years, field applications of tribenuron-methyl have been ineffective in controlling S. conoidea in Hebei Province, China. The aim of this study was to determine the molecular basis of tribenuron-methyl resistance in S. conoidea. Whole-plant response assays revealed that the resistant population (R) exhibited a higher level of resistance (382.3-fold) to tribenuron-methyl. The R population also showed high cross-resistance to other acetolactate synthase (ALS) inhibitors, including imazethapyr, bispyribac-sodium and florasulam. However, the R population could be controlled by the field-recommended rates of bentazone, MCPA, fluroxypyr, carfentrazone-ethyl and bromoxynil. In vitro ALS activity assays indicated that the tribenuron-methyl I₅₀ value for the R population was 18.5 times higher than those for the susceptible population (S). ALS gene sequencing revealed an amino acid mutation, Trp-574-Leu, in the R population. Pretreatment with the P450 inhibitor malathion indicated that the R population might have cytochrome P450-mediated metabolic resistance. These results suggest that the Trp-574-Leu mutation and P450-mediated enhanced metabolism coexist in S. conoidea to generate tribenuron-methyl resistance. This is the first time that target-site and non-target-site resistance to tribenuron-methyl has been reported in S. conoidea.

Resistance to ALS inhibitors conferred by non-target-site resistance mechanisms in Myosoton aquaticum L

Myosoton aquaticum L. is a competitive broadleaf weed commonly found in wheat fields in China and has become challenging due to its evolving herbicide resistance. In this study, one subpopulation, RF1 (derived from the tribenuron-methyl-resistant population HN10), with none of the known acetolactate synthase (ALS) resistance mutations was confirmed to exhibit resistance to tribenuron-methyl (SU), pyrithiobac‑sodium (PTB), florasulam (TP), flucarbazone-Na (SCT), and diflufenican (PDS). In vitro ALS activity assays showed that the total ALS activity of RF1 was lower than that of the susceptible (S) population. However, there was no difference in ALS gene expression induced by tribenuron-methyl between the two populations. The combination of the cytochrome P450 monooxygenase (P450) inhibitor malathion and tribenuron-methyl resulted in the RF1 population behaving like the S population. The rapid P450-mediated tribenuron-methyl metabolism in RF1 plants was also confirmed by liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. In addition, approximately equal glutathione S-transferase (GST) activity was observed in RF1 and S plants of untreated and tribenuron-methyl treated groups. This study reported one M. aquaticum L. population without ALS resistance mutations exhibiting resistance to ALS inhibitors and the PDS inhibitor diflufenican, and the non-target-site resistance mechanism played a vital role in herbicide resistance.

Expression Pattern of Entire Cytochrome P450 Genes and Response of Defenses in a Metabolic-Herbicide-Resistant Biotype of Polypogon fugax

Enhanced herbicide metabolism mediated by cytochrome P450s has been proposed as one of the major mechanisms of resistance to fenoxaprop-P-ethyl in a metabolic-herbicide-resistant biotype of Asia minor bluegrass (Polypogon fugax Nees ex Steud.). Upon pre-treatment with the P450 inhibitor piperonyl butoxide, a remarkable reduction in metabolic rates of the phytotoxic fenoxaprop-P has been observed in the resistant plants, implying that constitutive and/or fenoxaprop-P-ethyl-induced up-regulation of specific P450 isoforms are involved in the fenoxaprop-P-ethyl resistance. However, which P450 gene(s) were responsible for the metabolic resistance is still unknown. In this present study, based on the abundant gene resources of P. fugax established previously, a total of 48 putative P450 genes were isolated from the metabolic-herbicide-resistant plants and used for gene expression analysis. The most suitable reference genes for accurate normalization of real-time quantitative PCR data were first identified in P. fugax and recognized as actin (ACT), 18S rRNA (18S), and ribulose-1,5-bisphosphate carboxylase oxygenase (RUBP) under fenoxaprop-P-ethyl stress, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and elongation factor 1α (EF1α) under mesosulfuron-methyl stress, and ACT, EF1α, eukaryotic initiation factor 4a (EIF4A), and 25S rRNA (25S) at different growth stages. Expression analysis of the putative P450 genes revealed that six genes, respectively, annotated as CYP709B1, CYP71A1-4, CYP711A1, CYP78A9, P450-11, and P450-39 were up-regulated more than 10-fold in the resistant plants by fenoxaprop-P-ethyl treatment, and all of them exhibited constitutively and/or herbicide-induced higher transcript levels in the fenoxaprop-P-ethyl-resistant than in the susceptible plants. Three genes, respectively, annotated as CYPRO4, CYP313A4, and CYP51H11 constantly up-regulated in the resistant than in the susceptible plants after fenoxaprop-P-ethyl treatment. Up-regulated expressions of these specific P450 genes were consistent with the higher P450 contents determined in the resistant plants. These results will help to elucidate the mechanisms for P450-mediated metabolic-herbicide resistance in P. fugax as well as other grass weed species.

Cytochrome P450 CYP709C56 metabolizing mesosulfuron-methyl confers herbicide resistance in Alopecurus aequalis

Multiple herbicide resistance in diverse weed species endowed by enhanced herbicide detoxification or degradation is rapidly growing into a great threat to herbicide sustainability and global food safety. Although metabolic resistance is frequently documented in the economically damaging arable weed species shortawn foxtail (Alopecurus aequalis Sobol.), relevant molecular knowledge has been lacking. Previously, we identified a field population of A. aequalis (R) that had evolved metabolic resistance to the commonly used acetolactate synthase (ALS)-inhibiting herbicide mesosulfuron-methyl. RNA sequencing was used to discover potential herbicide metabolism-related genes, and four cytochrome P450s (CYP709C56, CYP71R18, CYP94C117, and CYP94E14) were identified with higher expressions in the R vs. susceptible (S) plants. Here the full-length P450 complementary DNA transcripts were each cloned with identical sequences between the S and R plants. Transgenic Arabidopsis overexpressing CYP709C56 became resistant to the sulfonylurea herbicide mesosulfuron-methyl and the triazolo-pyrimidine herbicide pyroxsulam. This resistance profile generally but does not completely in accordance with what is evident in the R A. aequalis. Transgenic lines exhibited enhanced capacity for detoxifying mesosulfuron-methyl into O-demethylated metabolite, which is in line with the detection of O-demethylated herbicide metabolite in vitro in transformed yeast. Structural modeling predicted that mesosulfuron-methyl binds to CYP709C56 involving amino acid residues Thr-328, Thr-500, Asn-129, Gln-392, Phe-238, and Phe-242 for achieving O-demethylation. Constitutive expression of CYP709C56 was highly correlated with the metabolic mesosulfuron-methyl resistance in A. aequalis. These results indicate that CYP709C56 degrades mesosulfuron-methyl and its up-regulated expression in A. aequalis confers resistance to mesosulfuron-methyl.

Identification of essential genes involved in metabolism-based resistance mechanism to fenoxaprop-P-ethyl in Polypogon fugax

BACKGROUND

Metabolic resistance is a worldwide concern for weed control but has not yet been well-characterized at the genetic level. Previously, we have identified an Asia minor bluegrass (Polypogon fugax Nees ex Steud.) population AHHY exhibiting cytochrome P450 (P450)-involved metabolic resistance to fenoxaprop-P-ethyl. In this study, we aimed to confirm the metabolic fenoxaprop-P-ethyl resistance in AHHY and uncover the potential herbicide metabolism-related genes in this economically damaging weed species.

RESULTS

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays indicated the metabolic rates of fenoxaprop-P-ethyl were significantly faster in resistant (R, AHHY) than in susceptible (S, SDTS) plants. The amount of phytotoxic fenoxaprop-P peaked at 12 h after herbicide treatment (HAT) and started to decrease at 24 HAT in both biotypes. R and S plants at 24 HAT were sampled to conduct isoform-sequencing (Iso-Seq) and RNA-sequencing (RNA-Seq). A reference transcriptome containing 24 972 full-length isoforms was obtained, of which 24 329 unigenes were successfully annotated. Transcriptomic profiling identified 28 detoxifying enzyme genes constitutively and/or herbicide-induced up-regulated in R than in S plants. Real-time quantitative polymerase chain reaction (RT-qPCR) confirmed 17 genes were consistently up-regulated in R and its F1 generation plants. They were selected as potential fenoxaprop-P-ethyl metabolism-related genes, including ten P450s, one glutathione-S-transferase, one UDP-glucosyltransferase, and five adenosine triphosphate (ATP)-binding cassette transporters.

CONCLUSION

This study revealed that the enhanced rates of fenoxaprop-P-ethyl metabolism in P. fugax were very likely driven by the herbicide metabolism-related genes. The transcriptome data generated by Iso-Seq combined with RNA-Seq will provide abundant gene resources for understanding the molecular mechanisms of resistance in P. fugax.

Accumulation of Target Gene Mutations Confers Multiple Resistance to ALS, ACCase, and EPSPS Inhibitors in Lolium Species in Chile

Different Lolium species, common weeds in cereal fields and fruit orchards in Chile, were reported showing isolated resistance to the acetyl CoA carboxylase (ACCase), acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibiting herbicides in the late 1990s. The first case of multiple resistance to these herbicides was Lolium multiflorum found in spring barley in 2007. We hypothesized that other Lolium species may have evolved multiple resistance. In this study, we characterized the multiple resistance to glyphosate, diclofop-methyl and iodosulfuron-methyl-sodium in Lolium rigidum, Lolium perenne and Lolium multiflorum resistant (R) populations from Chile collected in cereal fields. Lolium spp. populations were confirmed by AFLP analysis to be L. rigidum, L. perenne and L. multiflorum. Dose-response assays confirmed multiple resistance to glyphosate, diclofop-methyl and iodosulfuron methyl-sodium in the three species. Enzyme activity assays (ACCase, ALS and EPSPS) suggested that the multiple resistance of the three Lolium spp. was caused by target site mechanisms, except the resistance to iodosulfuron in the R L. perenne population. The target site genes sequencing revealed that the R L. multiflorum population presented the Pro-106-Ser/Ala (EPSPS), Ile-2041-Asn++Asp-2078-Gly (ACCase), and Trp-574-Leu (ALS) mutations; and the R L. rigidum population had the Pro-106-Ser (EPSPS), Ile-1781-Leu+Asp-2078-Gly (ACCase) and Pro-197-Ser/Gln+Trp-574-Leu (ALS) mutations. Alternatively, the R L. perenne population showed only the Asp-2078-Gly (ACCase) mutation, while glyphosate resistance could be due to EPSPS gene amplification (no mutations but high basal enzyme activity), whereas iodosulfuron resistance presumably could involve non-target site resistance (NTSR) mechanisms. These results support that the accumulation of target site mutations confers multiple resistance to the ACCase, ALS and EPSPS inhibitors in L. multiflorum and L. rigidum from Chile, while in L. perenne, both target and NTSR could be present. Multiple resistance to three herbicide groups in three different species of the genus Lolium in South America represents a significant management challenge.

Herbicide resistant weeds: A call to integrate conventional agricultural practices, molecular biology knowledge and new technologies

Herbicide resistant (HR) weeds are of major concern in modern agriculture. This situation is exacerbated by the massive adoption of herbicide-based technologies along with the overuse of a few active ingredients to control weeds over vast areas year after year. Also, many other anthropological, biological, and environmental factors have defined a higher rate of herbicide resistance evolution in numerous weed species around the world. This review focuses on two central points: 1) how these factors have affected the resistance evolution process; and 2) which cultural practices and new approaches would help to achieve an effective integrated weed management. We claim that global climate change is an unnoticed factor that may be acting on the selection of HR weeds, especially those evolving into non-target-site resistance mechanisms. And we present several new tools -such as Gene Drive and RNAi technologies- that may be adopted to cope with herbicide resistance spread, as well as discuss their potential application at field level. This is the first review that integrates agronomic and molecular knowledge of herbicide resistance. It covers not only the genetic basis of the most relevant resistance mechanisms but also the strengths and weaknesses of traditional and forthcoming agricultural practices.

A Trp-574-Leu mutation in the acetolactate synthase (ALS) gene of Lithospermum arvense L. confers broad-spectrum resistance to ALS inhibitors

Lithospermum arvense is a troublesome dicotyledonous winter annual weed of wheat in China. A L. arvense population (HN01) suspected of being resistant to acetolactate synthase (ALS) inhibitors was found in Henan Province, China. This study aimed to testify the sensitivity of this HN01 population to eight herbicides from 3 different modes of action, and to explore the potential target-site-resistance mechanism to tribenuron-methyl. The whole-plant bioassays indicated that the population was highly resistant to tribenuron-methyl (SU, 350-fold), pyrithiobac sodium (PTB, 151-fold), pyroxsulam (TP, 62.7-fold), florasulam (TP, 80.6-fold), and imazethapyr (IMI, 136-fold), but was sensitive to carfentrazone-ethyl and fluroxypyr-meptyl. ALS gene sequencing revealed that the Trp (TGG) was substituted by Leu (TTG) at codon 574 in resistant plants. In in vitro ALS assays, the concentration of tribenuron-methyl required to inhibit 50% ALS activity (I₅₀) for HN01 was 117-fold greater than that required to inhibit a susceptible population (HN05), indicating that resistance was due to reduced sensitivity of the ALS enzyme to tribenuron-methyl. To the best of our knowledge, this is the first report of ALS gene Trp-574-Leu amino acid mutation confer resistance to tribenuron-methyl in L. arvense.

Unravelling mesosulfuron-methyl phytotoxicity and metabolism-based herbicide resistance in Alopecurus aequalis: Insight into regulatory mechanisms using proteomics

Non-target-site based resistance (NTSR), a poorly understood multigenic trait, has evolved as the greatest threat to crop production worldwide, by endowing weed plants an unpredictable pattern of resistance to herbicides. Our recent work with multiple-herbicide-resistant shortawn foxtail (Alopecurus aequalis Sobol.) biotype has preliminary indicated that cytochrome P450s-involved enhanced rate of mesosulfuron-methyl metabolism may involve in the NTSR. Here by further determining the differences in glutathione S-transferase (GST) activity and uptake and metabolic rates of mesosulfuron between resistant (R) and susceptible (S) A. aequalis plants, and associating them with endogenous differently regulated proteins (DEPs) identified from combinational proteomics analyses, we provided direct evidences on the enhanced herbicide degradation in resistant plants. Subsequently, the physiological phenotypes of photosynthesis, chlorophyll fluorescence, and antioxidation were compared between R and S plants and linked with correlative DEPs, indicating a series of key pathways including solar energy capture, photosynthetic electron transport, redox homeostasis, carbon fixation, photorespiration, and reactive oxygen species scavenging in susceptible plants were broken or severely damaged by mesosulfuron stress. In comparison, resistant plants have evolved enhanced herbicide degradation to minimize the accumulation of mesosulfuron and protect the photosynthesis and ascorbate-glutathione cycle against the adverse effects of chemical injury, giving A. aequalis plants a NTSR phenotype. Additionally, three key proteins respectively annotated as esterase, GST, and glucosyltransferase were identified and enabled as potential transcriptional markers for quick diagnosing the metabolic mesosulfuron resistance in A. aequalis species.