Effect of mutations on acetohydroxyacid synthase(AHAS)function in Cyperus difformis L.

Cyperus difformis L.is a troublesome weed in paddy fields and has attracted attention due to its resistance to acetohydroxyacid synthase(AHAS)inhibitors.It was found that the amino acid mutation in AHAS was the primary cause for the resistance of Cyperus difformis.However,the effect of different mutations on AHAS function is not clear in Cyperus difformis.To confirm the effect of mutations on AHAS function,six biotypes were collected,including Pro197Arg,Pro197Ser,Pro197Leu,Asp376Glu,Trp574Leu and wild type,from Hunan,Anhui,Jiangxi and Jiangsu provinces,China and the function of AHAS was characterized.The AHAS in vitro inhibition assay results indicated that the mutations decreased the sensitivity of AHAS to pyrazosulfuron-ethyl,in which the I_(50)(the half maximal inhibitory concentration)of wild type AHAS was 0.04μmol L^(-1)and Asp376Glu,Pro197Leu,Pro197Arg,Pro197Ser and Trp574Leu mutations were 3.98,11.50,40.38,38.19 and 311.43μmol L^(-1),respectively.In the determination of enzyme kinetics parameters,the Km and the maximum reaction velocity(Vmax)of the wild type were 5.18 mmol L^(-1)and 0.12 nmol mg^(-1)min^(-1),respectively,and the Km values of AHAS with Asp376Glu,Trp574Leu,Pro197Leu and Pro197Ser mutations were 0.38-0.93 times of the wild type.The Km value of the Pro197Arg mutation was 1.14times of the wild type,and the Vmax values of the five mutations were 1.17-3.33-fold compared to the wild type.It was found that the mutations increased the affinity of AHAS to the substrate,except for the Pro197Arg mutation.At a concentration of 0.0032-100 mmol L^(-1)branched-chain amino acids(BCAAs),the sensitivity of the other four mutant AHAS biotypes to feedback inhibition decreased,except for the Pro197Arg mutation.This study elucidated the effect of different mutations on AHAS function in Cyperus difformis and provided ideas for further study of resistance development.

Development and molecular analysis of a novel acetohydroxyacid synthase rapeseed mutant with high resistance to sulfonylurea herbicides

With the increasing promotion of simplified rapeseed cultivation in recent years,the development of cultivars with high resistance to herbicides is urgently needed.We previously developed M342,which shows sulfonylurea herbicide resistance,by targeting acetohydroxyacid synthase(AHAS),a key enzyme in branched-chain amino acid synthesis.In the present study,we used a progeny line derived from M342 for an additional round of ethyl methane sulfonate mutagenesis,yielding the novel mutant DS3,which harbored two mutations in AHAS genes and showed high sulfonylurea resistance.One mutation was the substitution Trp574 Leu,as in M342,according to Arabidopsis protein sequencing.The other site was a newly recognized substitution,Pro197 Leu.A KASP marker targeting Pro197 Leu was developed and reliably predicted the response to sulfonylurea herbicides in the F2 population.The combination of Trp574 Leu and Pro197 Leu in DS3 produced a synergistic effect that greatly increased herbicide resistance.Analysis of the protein structures of AHAS1 and AHAS3 in wild-type and single-gene mutant plants revealed three-dimensional protein conformational changes that could account for differences in herbicide resistance characteristics including toxicity tolerance,AHAS enzyme activity,and AHAS gene expression.

Synthesis and Characterization of Novel Acetohydroxyacid Synthase Inhibitors

A novel kind of acetohydroxyacid synthase（AHAS） inhibitors, arylsulfonylaminocarbonyl-2-thiohydantoins, was synthesized based on biorational design. The structures of these compounds were confirmed by IR, MS, NMR, and elemental analysis. The results of the preliminary activity tests indicate that most of the arylsulfonylamidecarbonyl-5- methyl-2-thiohydantoins have a higher biological activity than those without 5-methyl substituent.

Molecular Drug Resistance Prediction for Acetohydroxyacid Synthase Mutants Against Chlorsulfuron Using MB-QSAR

Chlorsulfuron is the first commercialized sulfonylurea herbicide, which targets acetohydroxyacid synthase （AHAS）. Mutations in AHAS have caused serious herbicide resistance to chlorsulfuron. Quantitative description of the herbicide resistance in molecular level will benefit the understanding of the resistance mechanism and aid the design of resistance-evading herbicide. We have recently established a MB-QSAR （Mutation-dependent Biomac- romolecular Quantitative Structure-Activity Relationship） method to conduct the 3D-QSAR study in biomacro- molecules. Herein, based on the herbicide resistance data measured for a series of AHAS mutants against chlorsul- furon, we constructed MB-QSAR models to quantitatively predict the herbicide resistance and interpret the struc- ture resistance relationships for AHAS mutants against chlorsulfuron. Quite well correlations between the experi- mental and the predicted pKi values were achieved for MB-QSAR/CoMFA （q^2=0.705, r^2=0.918, r^2pred=0.635） and MB-QSAR/CoMSIA （q^2=0.558, r^2=0.940, r^2pred=0.527） models, and interpretation of the MB-QSAR models gave chemical intuitive information to guide the resistance-evading herbicide design.

Synthesis and Characterization of Novel-4-Methyl-3-isoxazolidinone Derivatives

A novel type of aeetohydrexyacid synthase inhibitors, 4-methyl-3-isoxazolidinone derivatives of sulfonylurea, was designed and synthesized. The structures of these compounds were confirmed by using MS, NMR, and elemental analysis. The results of preliminary active tests indicate that the compounds show a herbicidal activity.

Synthesis and Herbicidal Activity of Novel Phenoxysulfonylureas Derivatives

Thirteen novel phenoxysulfonylureas derivatives were synthesized, and their structures were confirmed by MS, NMR and element analysis. The herbicidal activity and structure-activity relationship were also investigated. The results of preliminary active tests indicate that the compounds show moderate herbicidal activity.

Design, Syntheses and Biological Activities of Novel Sulfonylureas Containing an Oxime Ether Moiety

Since sulfonylurea is one of the most potent acetohydroxyacid synthase（AHAS） inhibitors, a series of novel sulfonylureas containing an oxime ether moiety was designed and synthesized and their chemical structures were determined by means of 1H nuclear magnetic resonance（NMR）, 13C NMR and high-resolution mass spectrometry（HRMS）. In the herbicidal bioassay, several compounds showed moderate to good herbicidal activities against dicotyledons, but their activities against monocotyledons decreased. The in vitro antifungal activity was tested at a dosage of 50 mg/L. And the results show that compounds 71, 7m and 7n exhibit promising antifungal activities against six common plant pathogenic fungi. Further investigations on molecular modification are in progress.

Synthesis and Evaluation of Novel N-（4＇-Arylpyrimidin-2＇-yl） Sulfonylurea Derivatives as Potential Antifungal Agents

Sulfonylureas（SUs） are potent and selective inhibitors of acetohydroxyacid synthase and has been used as herbicides. Some SUs also displayed other biological activities. In order to discuss the antifungal activity of SUs, a series of novel SUs containing aryl-substituted pyrimidine moieties was designed and synthesized. The preliminary bioassay showed that the title compounds exhibited moderate to favorable fungicidal activities in vivo. Especially, compound 9b exhibited more efficacy than the controls against five fungi at 25 mg/L. These promising results indicate that an aryl group on pyrimidine ring is favorable for antifungal activity and SUs are potential inhibitors for some phytopathogenic fungi.