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Xenobiotic responsiveness of Arabidopsis thaliana to a chemical series derived from a herbicide safener.

ABSTRACT: Plants respond to synthetic chemicals by eliciting a xenobiotic response (XR) that enhances the expression of detoxifying enzymes such as glutathione transferases (GSTs). In agrochemistry, the ability of safeners to induce an XR is used to increase herbicide detoxification in cereal crops. Based on the responsiveness of the model plant Arabidopsis thaliana to the rice safener fenclorim (4,6-dichloro-2-phenylpyrimidine), a series of related derivatives was prepared and tested for the ability to induce GSTs in cell suspension cultures. The XR in Arabidopsis could be divided into rapid and slow types depending on subtle variations in the reactivity (electrophilicity) and chemical structure of the derivatives. In a comparative microarray study, Arabidopsis cultures were treated with closely related compounds that elicited rapid (fenclorim) and slow (4-chloro-6-methyl-2-phenylpyrimidine) XRs. Both chemicals induced major changes in gene expression, including a coordinated suppression in cell wall biosynthesis and an up-regulation in detoxification pathways, whereas only fenclorim selectively induced sulfur and phenolic metabolism. These transcriptome studies suggested several linkages between the XR and oxidative and oxylipin signaling. Confirming links with abiotic stress signaling, suppression of glutathione content enhanced GST induction by fenclorim, whereas fatty acid desaturase mutants, which were unable to synthesize oxylipins, showed an attenuated XR. Examining the significance of these studies to agrochemistry, only those fenclorim derivatives that elicited a rapid XR proved effective in increasing herbicide tolerance (safening) in rice.

SUBMITTER: Skipsey M

PROVIDER: S-EPMC3173150 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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Xenobiotic responsiveness of Arabidopsis thaliana to a chemical series derived from a herbicide safener.

Skipsey Mark M Knight Kathryn M KM Brazier-Hicks Melissa M Dixon David P DP Steel Patrick G PG Edwards Robert R

The Journal of biological chemistry 20110721 37

Plants respond to synthetic chemicals by eliciting a xenobiotic response (XR) that enhances the expression of detoxifying enzymes such as glutathione transferases (GSTs). In agrochemistry, the ability of safeners to induce an XR is used to increase herbicide detoxification in cereal crops. Based on the responsiveness of the model plant Arabidopsis thaliana to the rice safener fenclorim (4,6-dichloro-2-phenylpyrimidine), a series of related derivatives was prepared and tested for the ability to i ...[more]

PMID: 21778235

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Project description:The safener fenclorim (4,6-dichloro-2-phenylpyrimidine) increases tolerance to chloroacetanilide herbicides in rice by enhancing the expression of detoxifying glutathione S-transferases (GSTs). Fenclorim also enhances GSTs in Arabidopsis thaliana, and while investigating the functional significance of this induction in suspension cultures, we determined that these enzymes glutathionylated the safener. The resulting S-(fenclorim)-glutathione conjugate was sequentially processed to S-(fenclorim)-gamma-glutamyl-cysteine and S-(fenclorim)-cysteine (FC), the latter accumulating in both the cells and the medium. FC was then either catabolized to 4-chloro-6-(methylthio)-phenylpyrimidine (CMTP) or N-acylated with malonic acid. These cysteine derivatives had distinct fates, with the enzymes responsible for their formation being induced by fenclorim and FC. Fenclorim-N-malonylcysteine was formed from FC by the action of a malonyl-CoA-dependent N-malonyltransferase. A small proportion of the fenclorim-N-malonylcysteine then underwent decarboxylation to yield a putative S-fenclorim-N-acetylcysteine intermediate, which underwent a second round of GST-mediated S-glutathionylation and subsequent proteolytic processing. The formation of CMTP was catalyzed by the concerted action of a cysteine conjugate beta-lyase and an S-methyltransferase, with the two activities being coordinately regulated. Although the fenclorim conjugates tested showed little GST-inducing activity in Arabidopsis, the formation of CMTP resulted in metabolic reactivation, with the product showing good enhancing activity. In addition, CMTP induced GSTs and herbicide-safening activity in rice. The bioactivated CMTP was in turn glutathione-conjugated and processed to a malonyl cysteine derivative. These results reveal the surprisingly complex set of competing catabolic reactions acting on xenobiotics entering the S-glutathionylation pathway in plants, which can result in both detoxification and bioactivation.

Project description:The use of herbicide safeners can significantly alleviate herbicide injury to protect crop plants and expand the application scope of the existing herbicides in the field. Sanshools, which are well known as spices, are N-alkyl substituted compounds extracted from the Zanthoxylum species and have several essential physiological and pharmacological functions. Sanshools display excellent safener activity for the herbicide metolachlor in rice seedlings. However, the high cost of sanshools extraction and difficulties in the synthesis of their complicated chemical structures limit their utilization in agricultural fields. Thus, the present study designed and synthesized various N-alkyl amide derivatives via the scaffold-hopping strategy to solve the challenge of complicated structures and find novel potential safeners for the herbicide metolachlor. In total, 33 N-alkyl amide derivatives (2a-k, 3a-k, and 4a-k) were synthesized using amines and saturated and unsaturated fatty acids as starting materials through acylation and condensation. The identity of all the target compounds was well confirmed by 1H-NMR, 13C-NMR, and high-resolution mass spectrometry (HRMS). The primary evaluation of safener activities for the compounds by the agar method indicated that most of the target compounds could protect rice seedlings from injury caused by metolachlor. Notably, compounds 2k and 4k displayed excellent herbicide safener activities on plant height and demonstrated relatively similar activities to the commercialized compound dichlormid. Moreover, we showed that compounds 2k and 4k had higher glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO) activities in rice seedlings, compared to the metolachlor treatment. In particular, 2k and 4k are safer for aquatic organisms than dichlormid. Results from the current work exhibit that compounds 2k and 4k have excellent crop safener activities toward rice and can, thus, be promising candidates for further structural optimization in rice protection.

Dataset Information

Xenobiotic responsiveness of Arabidopsis thaliana to a chemical series derived from a herbicide safener.

Publications

Xenobiotic responsiveness of Arabidopsis thaliana to a chemical series derived from a herbicide safener.

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