Herbicides that Inhibit Acetohydroxyacid Synthase

Abstract

Acetohydroxyacid synthase was discovered as the site of action of imidazolinone and sulfonylurea herbicides over 6 yr ago. In recent years, advances have been made in the understanding of this enzyme as a herbicide target site. Derivatives of both imidazolinones and sulfonylureas have yielded new herbicide chemistry. AH of the herbicides display unusual “slow-binding” behavior with the enzyme, and this behavior may help explain efficacy of the herbicides. Resistance to these herbicides has been developed through a number of different procedures, and the mechanism of resistance is through changes in sensitivity of the enzyme to the herbicides. The changes are either selective to only one class of chemistry, or broad to a number of classes of chemistry. These data support the idea that binding sites for the herbicides on the enzyme are only partially overlapping. Progress in purification of AHAS from corn includes discovery of the existence of the enzyme in monomer and oligomer aggregation states. The interaction of the enzyme with the herbicides is affected by enzyme aggregation state.

A novel amino acid substitution Trp574Arg in acetolactate synthase (ALS) confers broad resistance to ALS‐inhibiting herbicides in crabgrass (Digitaria sanguinalis)

“…ALS is a key enzyme in biosynthesis of the branched‐chain amino acids – valine, leucine and isoleucine – and is the target site of many commercial herbicides. Five structurally distinct chemical classes of herbicides inhibit ALS activity: sulfonylureas (SUs), imidazolinones (IMIs), triazolopyrimidines (TPs), pyrimidinylthiobenzoates (PTBs) and sulfonylamino‐carbonyl‐triazolinones (SCTs) . The first ALS‐resistant weed species ( Lolium rigidum ) was found in 1982 .…”

A novel Pro197Glu substitution in acetolactate synthase (ALS) confers broad-spectrum resistance across ALS inhibitors

“…ALS is the common target site of five commercially used herbicides, including sulfonylurea (SU), pyrimidinylthiobenzoate (PTB), triazolopyrimidine (TP), sulfonylaminocarbonyltriazolinone (SCT) and imidazolinone (IMI) [3][4][5][6][7]. ALS inhibitors bind at the substrate access channel of ALS, blocking the path of the substrate to the active site and inhibiting ALS, with subsequent plant death [8][9][10].…”

Development and Genetic Characterization of A Novel Herbicide (Imazethapyr) Tolerant Mutant in Rice (Oryza sativa L.)

“…In weeds, Ala122, Pro197, Ala205, Asp 376 , Arg 377 , Trp574, Ser653 and Gly 654 are the eight confirmed target sites reported across genera and countries so far (http://www.weedscience.com/Mutations/MutationDisplayAll.aspx; accessed on 21 Nov 2016). In weedy rice alone, three mutations, G654E, S653D and A122T are known (Roso et al 2010). Among them, the change S653D (S627D in rice) is common across crops and weeds (Croughan 2002) whereas the rice Clearfield events released in USA had mutation G654E (G628E in rice) as known from the patent search (US 20070028318 A1).…”