An acetohydroxy acid synthase mutant reveals a single site involved in multiple herbicide resistance

Hattori, Jiro; Brown, Douglas; Mourad, George; Labbé, Hélène; Ouellet, Thérèse; Sunohara, Glen; Rutledge, Robert G.; King, John; Miki, Brian

doi:10.1007/bf00290445

Cited by 81 publications

(60 citation statements)

References 41 publications

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“…Both S653N (19,20) and A122T (17) confer strong resistance to the imidazolinones but not to the sulfonylureas. A122 makes important hydrophobic contacts to the isopropyl, and methyl substituents of the dihydroimidazolone ring and mutation to a larger polar residue, such as threonine, would tend to dislodge the herbicide from its site.…”

Section: Sulfonylurea and Imidazolinone Binding To Atahasmentioning

confidence: 99%

Herbicide-binding sites revealed in the structure of plant acetohydroxyacid synthase

McCourt

Pang

King-Scott

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

321

340

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The sulfonylureas and imidazolinones are potent commercial herbicide families. They are among the most popular choices for farmers worldwide, because they are nontoxic to animals and highly selective. These herbicides inhibit branched-chain amino acid biosynthesis in plants by targeting acetohydroxyacid synthase (AHAS, EC 2.2.1.6). This report describes the 3D structure of Arabidopsis thaliana AHAS in complex with five sulfonylureas (to 2.5 Å resolution) and with the imidazolinone, imazaquin (IQ; 2.8 Å). Neither class of molecule has a structure that mimics the substrates for the enzyme, but both inhibit by blocking a channel through which access to the active site is gained. The sulfonylureas approach within 5 Å of the catalytic center, which is the C2 atom of the cofactor thiamin diphosphate, whereas IQ is at least 7 Å from this atom. Ten of the amino acid residues that bind the sulfonylureas also bind IQ. Six additional residues interact only with the sulfonylureas, whereas there are two residues that bind IQ but not the sulfonylureas. Thus, the two classes of inhibitor occupy partially overlapping sites but adopt different modes of binding. The increasing emergence of resistant weeds due to the appearance of mutations that interfere with the inhibition of AHAS is now a worldwide problem. The structures described here provide a rational molecular basis for understanding these mutations, thus allowing more sophisticated AHAS inhibitors to be developed. There is no previously described structure for any plant protein in complex with a commercial herbicide.inhibition ͉ sulfonylurea ͉ x-ray crystallography ͉ imidazolinone ͉ thiamin diphosphate T he sulfonylurea and imidazolinone herbicides are an essential part of the multibillion-dollar weed-control market. There are now Ͼ30 herbicides from these families registered for worldwide use. A major advantage of these compounds is that they are nontoxic to animals, highly selective, and very potent, thereby allowing low application rates. These herbicides act by inhibiting acetohydroxyacid synthase [AHAS; also known as acetolactate synthase; EC 2.2.1.6 (1)], the first common enzyme in the biosynthetic pathway of the branched-chain amino acids. The reaction carried out by this enzyme is the synthesis of either (S)-2-acetolactate from two molecules of pyruvate or (S)-2-aceto-2-hydroxybutyrate from a molecule each of pyruvate and 2-ketobutyrate.AHAS belongs to a superfamily of thiamin diphosphate (ThDP)-dependent enzymes that are capable of catalyzing a variety of reactions, including both the oxidative and nonoxidative decarboxylation of 2-ketoacids. This cofactor is bound by a divalent metal ion such as Mg 2ϩ , which coordinates to the diphosphate group of ThDP and to two highly conserved residues (2) in these proteins. AHAS also binds a molecule of FAD, although this cofactor does not participate in the principal reactions. To date, most AHAS enzymes that have been characterized have both a catalytic subunit (Ϸ65 kDa) and a smaller regulatory subunit, which varies in s...

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Section: Sulfonylurea and Imidazolinone Binding To Atahasmentioning

confidence: 99%

Herbicide-binding sites revealed in the structure of plant acetohydroxyacid synthase

McCourt

Pang

King-Scott

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

321

340

View full text Add to dashboard Cite

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“…The Arabidopsis AHAS gene [24] was obtained from Dr. B. Miki and Dr. J. Hattori (Plant Research Centre, Agriculture Canada) as the plasmid pALSTX containing a 5n5 kb fragment comprising the AHAS promoter region, the entire coding region and the 3h-non-coding region. The AHAS gene contains NcoI site at the first codon.…”

Section: Construction Of Recombinant Plasmidsmentioning

confidence: 99%

Expression, purification and characterization of Arabidopsis thaliana acetohydroxyacid synthase

Chang

Duggleby

1997

Biochemical Journal

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Acetohydroxyacid synthase (EC 4;1;3;18) is the enzyme that catalyses the first step in the synthesis of the branched-chain amino acids valine, leucine and isoleucine. The AHAS gene from Arabidopsis thaliana with part of the chloroplast transit sequence removed was cloned into the bacterial expression vector pT7-7 and expressed in the Escherichia coli strain BL21(DE3). The expressed enzyme was purified by an extensive procedure involving (NH % ) # SO % fractionation followed by hydrophobic and anion-exchange chromatography. The purified enzyme appears as a single band on SDS\PAGE with a molecular mass of about 61 kDa. On gel filtration the enzyme is a dimer, migrating as a single peak with molecular masses of 109 and 113 kDa in the absence and presence of FAD respectively. Ion spray MS analysis yielded a mass of 63 864 Da. The enzyme has optimum activity in

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“…Amino acid substitutions at Ala122 and Ser653 confer high levels of resistance to imidazolinone herbicides (IMIs), whereas substitutions at Pro197 endow high levels of resistance against sulfonylureas and provide low-level resistance against IMIs and triazolopyrimidine herbicides (18)(19)(20)(21)(22). Substitutions at Trp574 endow high levels of resistance to imidazolinones, sulfonylureas, and triazolopyrimidines (19,(23)(24)(25)(26), whereas substitutions at Ala205 provide resistance against all AHAS-inhibiting herbicides (24,27).…”

mentioning

confidence: 99%

Single nucleotide mutation in the barley acetohydroxy acid synthase ( AHAS ) gene confers resistance to imidazolinone herbicides

Lee¹,

Rustgi²,

Kumar³

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Induced mutagenesis can be an effective way to increase variability in self-pollinated crops for a wide variety of agronomically important traits. Crop resistance to a given herbicide can be of practical value to control weeds with efficient chemical use. In some crops (for example, wheat, maize, and canola), resistance to imidazolinone herbicides (IMIs) has been introduced through mutation breeding and is extensively used commercially. However, this production system imposes plant-back restrictions on rotational crops because of herbicide residuals in the soil. In the case of barley, a preferred rotational crop after wheat, a period of 9–18 mo is required. Thus, introduction of barley varieties showing resistance to IMIs will provide greater flexibility as a rotational crop. The objective of the research reported was to identify resistance in barley for IMIs through induced mutagenesis. To achieve this objective, a sodium azide-treated M 2 /M 3 population of barley cultivar Bob was screened for resistance against acetohydroxy acid synthase (AHAS)-inhibiting herbicides. The phenotypic screening allowed identification of a mutant line showing resistance against IMIs. Molecular analysis identified a single-point mutation leading to a serine 653 to asparagine amino acid substitution in the herbicide-binding site of the barley AHAS gene. The transcription pattern of the AHAS gene in the mutant (Ser653Asn) and WT has been analyzed, and greater than fourfold difference in transcript abundance was observed. Phenotypic characteristics of the mutant line are promising and provide the base for the release of IMI-resistant barley cultivar(s).

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An acetohydroxy acid synthase mutant reveals a single site involved in multiple herbicide resistance

Cited by 81 publications

References 41 publications

Herbicide-binding sites revealed in the structure of plant acetohydroxyacid synthase

Herbicide-binding sites revealed in the structure of plant acetohydroxyacid synthase

Expression, purification and characterization of Arabidopsis thaliana acetohydroxyacid synthase

Single nucleotide mutation in the barley acetohydroxy acid synthase ( AHAS ) gene confers resistance to imidazolinone herbicides

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