Catabolism of Glutathione Conjugates in Arabidopsis thaliana

Abstract

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)-␥-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-Nacetylcysteine 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 ␤-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.

Metabolism and Photolysis of 2,4-Dinitroanisole in Arabidopsis

“…This process has been described for glutathione conjugates of the herbicide safener, fenclorim, among other compounds, and has been attributed to intra-vacuolar peptidases, which successively cleave the glycinyl and glutamyl moieties from the attached glutathione (Figure 2B). 21, 42 Although the mass fragments enabled us to classify these metabolites as glutathione and cysteine conjugates, the transformation pathways and ultimate molecular structures could not be definitively determined.…”

The C-Glycosylation of Flavonoids in Cereals

“…Benzyl-2,4,6-trihydroxybenzoate (20) and 2-hydroxyflavanones (18) were prepared using previously described methods and purified by reversed-phase HPLC, and their identities were confirmed by mass spectrometry (MS) (21). Glucosyltransferase (CGT and OGT) activity was determined by incubating flavonoid acceptors (66 M) with UDP-[…”

“…Nipponbare) and wheat (T. aestivum cv. Einstein) seedlings were grown at 25°C for 10 days, and the shoots were extracted as described (21). Ammonium sulfate (0 -80% saturation) protein precipitates were resuspended in buffer A (20 mM Tris-HCl, pH 8.0, containing 2 mM dithiothreitol, adjusted to 1 M (NH 4 ) 2 SO 4 ) and applied (4 ml min Ϫ1 ) onto a phenylSepharose column (40 ml).…”

Genetic analysis of molecular markers for propamocarb residue in Cucumis sativus using quantitative trait locus mapping

“…For example, several studies have concentrated on the regulatory effects of cytochrome P450, glutathione, and the ABC transporter protein on pesticide metabolism in plants (Shiota et al, 1996;Brazier-Hicks et al, 2008;Meng et al, 2016). The GC technique has been widely used to analyze pesticide residues of relatively small molecular weight, high volatility, and heat-stability (González-Rodríguez et al, 2008;Swarnam and Velmurugan, 2013).…”