Herbicide Safener-Binding Protein of Maize1

Abstract

Herbicide safeners, also known as antidotes, are used to protect crops from herbicide injury (Hatzios, 1983(Hatzios, , 1989Fuerst, 1987). One important class of safeners is the dichloroacetamides, such as dichlormid, which are used in combination with thiocarbamate and chloroacetanilide herbicides on maize (Zea mays L.) and sorghum. Examples of these classes of compound are shown in Figure 1. Although it is well established that in maize dichloroacetamide safeners elevate GSH levels and induce novel GSH S-transferases, the mechanism by which they do so is not known (Lay et al., 1975;Fuerst et al., 1993).Etiolated maize seedlings contain a soluble, highaffinity-binding activity (K d , 0.12 m) for a tritiated form of the dichloroacetamide safener Saf (Fig. 1) (Walton and Casida, 1995). Although present in all tissues, SafBA is highest in the coleoptile. There is a good correlation between inhibition of Saf binding in vitro and safener action in vivo among a series of Saf analogs, with dichlormid, a widely used dichloroacetamide safener, being the strongest binding antagonist of any compound tested (IC 50 , 10 nm). Chloroacetanilide and thiocarbamate herbicides, which dichloroacetamide safeners protect against, are also strong competitive inhibitors of Saf binding; metolachlor and EPTC (Fig. 1) have IC 50 values of 110 and 40 nm, respectively (Walton and Casida, 1995). Despite their intensive use in agriculture for more than 30 years, the mode of action of these herbicides is currently unknown.To begin to address the question of the role of SafBA in the response of maize seedlings to dichloroacetamide safeners and, possibly, to the two classes of herbicides, we have further characterized SafBA. Here we report the purification of SafBP, immunological studies of its tissue and species distribution, and the cloning, sequencing, and expression in Escherichia coli of a cDNA encoding SafBP. MATERIALS AND METHODSGenotypes and sources of plant materials are as described by Walton and Casida (1995). The Arabidopsis thaliana ecotype was Columbia and the tobacco (Nicotiana tabacum) cultivar was SR-1. Plants were grown in the dark on wet paper towels for 4 to 7 d. Binding Assay Racemic Saf and [3 H]Saf (specific activity, 15 Ci/mmol) were prepared according to the method of Latli and Casida 1 This project was supported by Novartis, Inc., the Department of Energy, Division of Energy Biosciences (grant no. DEFG02-91ER20021 to J.D.W.), and the National Institute of Environmental Health Sciences (grant no. P01 ES00049 to J.E.C.).2 These two authors contributed equally to the experimental work.* Corresponding author; e-mail walton@pilot.msu.edu; fax 1-517-353-9168.Abbreviations: EPTC, S-ethyl dipropylthiocarbamate; IC 50 , inhibitor concentration that reduces specific binding by 50%; IPTG, isopropyl-␤-d-thiogalactopyranoside; OMT, O-methyltransferase; Saf, the dichloroacetamide safener (R,S)-3-dichloroacetyl-2,2,5-trimethyloxazolidine (also known as R-29148); SafBA, safenerbinding activity; SafBP, safener-binding protein.

Response of maize (Zea mays L.) to rimsulfuron under salt conditions

“…The analysis of total protein content indicates that accumulation of free amino compounds is not associated with protein degradation. An increase in total protein content in leaves may be due to synthesis and accumulation of stress proteins (Clayton and Reynolds 1991;Riccardi et al 1998;Scott-Craig et al 1998;Campalans et al 1999;Hasegawa et al 2000). In maize roots, a high concentration of free amino compounds was observed in the presence of 1 nmol·dm -3 rimsulfuron and 1 nmol·dm -3 rimsulfuron plus NaCl, whereas 100 nmol·dm -3 rimsulfuron plus NaCl had no effect.…”

Xenobiotic Responsiveness of Arabidopsis thaliana to a Chemical Series Derived from a Herbicide Safener

“…Similarly, other attempts to identify plant proteins that bind to safeners have proved inconclusive. In studies with the radiolabeled safener dichlormid (N,N-diallyl-2,2-dichloroacetamide), an apparently selective binding interaction to a methyltransferase of unknown function was determined in maize seedlings (8). However, the functional significance of this binding to eliciting safening in maize was not determined.…”

“…In agriculture, this response is exploited using safeners, a group of crop protection agents that increase the rates of detoxification of herbicides in cereal crops, thereby enhancing the selectivity of graminicides used to control competing grass weeds (7). Over the last 30 years a diverse range of safener chemistries have been developed, with each compound used in partnership with a herbicide for use in a specific crop (4,8). Although safening activity toward herbicides is only observed in cereals and some non-domesticated grasses (9), the ability of these compounds to selectively induce xenome enzymes also extends to dicotyledenous plants, such as poplar and Arabidopsis thaliana (6, 10 -12).…”

Daphnetin Methylation by a Novel O-Methyltransferase Is Associated with Cold Acclimation and Photosystem II Excitation Pressure in Rye

“…1B). However, the highest identity (57%) is observed with the maize herbicide Safener-binding protein, SafBP (22). A sequence alignment of these proteins shows five regions in the C-terminal portion (regions I to V, Fig.…”

“…This novel gene exhibits 26 to 40% amino acid sequence identity to a number of plant OMTs and is most closely related to SafBP, a Safener-binding protein that may protect maize against injury from chloroacetanilide and thiocarbamate herbicides (22), although it did not exhibit any enzymatic activity. This is not surprising because ScOMT1, but not SafBP, possesses in the first motif, the conserved aspartic acid residue proposed to be involved in the binding to AdoMet (29).…”