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) which 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 were prepared and tested for their 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 RNA-array study, Arabidopsis cultures were treated with closely-related compounds which elicited rapid (fenclorim) and slow (4-chloro-6-methyl-2-phenylpyrimidine;CMPP) XRs. Both chemicals induced major changes in gene expression, including a coordinated suppression in cell wall biosynthesis and an upregulation in detoxification pathways, while 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, while 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 which elicited a rapid XR proved effective in increasing herbicide tolerance (safening) in rice.