Key Role of Glutathione s-Transferase in Multiple-Herbicide Resistance in Grass Weeds

Abstact

Multiple-herbicide resistance (MHR) in black-grass (Alopecurus myosuroides ) and annual rye-grass (Lolium rigidum) is a global problem leading to a loss of chemical weed control in cereal crops. Although poorly understood, in common with multiple-drug resis- tance (MDR) in tumors, MHR is associated with an enhanced ability to detoxify xenobiotics. In humans, MDR is linked to the overex- pression of a pi class glutathione transferase (GSTP1), which has both detoxification and signaling functions in promoting drug re- sistance. In both annual rye-grass and black-grass, MHR was also associated with the increased expression of an evolutionarily dis- tinct plant phi (F) GSTF1 that had a restricted ability to detoxify herbicides. When the black-grass A. myosuroides (Am) AmGSTFI was expressed in Arabidopsis thaliana, the transgenic plants ac- quired resistance to multiple herbicides and showed similar changes in their secondary, xenobiotic, and antioxidant metabo- lism to those determined in MHR weeds. Transcriptome array experiments showed that these changes in biochemistry were not due to changes in gene expression. Rather, A/nGSTFI exerted a direct regulatory control on metabolism that led to an accumu- lation of protective flavonoids. Further evidence for a key role for this protein in MHR was obtained by showing that the GSTP1- and MDR-inhibiting pharmacophore 4-chloro-7-nitro-benzoxadiazole was also active toward AmGSTFI and helped restore herbicide control in MHR black-grass. These studies demonstrate a central role for specific GSTFs in MHR in weeds that has parallels with similar roles for unrelated GSTs in MDR in humans and shows their potential as targets for chemical intervention in resistant weed management.

Discussion/Key Point

• I chose to utilize this article in my blog post due to its importance to my personal research. I am currently conducting/creating an independent experimental protocol in the topic of biochemistry to perform over the summer. It follows my interests in phytoremediation/bioremediation and improving chemical exposure to the environment.
• The evolution of herbicide resistance in weeds is a global problem with serious implications to sustainable arable agriculture. The best-characterized resistance mechanisms arise from mutations in the proteins targeted by herbicides that lead to a reduced sensitivity to inhibition (target site-based resistance TSR). Mutations leading to TSR have been well described for the plastoquinone-binding protein of photosystem II and the acetyl CoA carboxylases and acetolactate synthases involved in fatty acid and branched chain amino acid biosynthesis, respectively.
• When functioning in a regulatory role, plant GSTs represent a tractable central mechanism for controlling plant stress responses and are already implicated in assuming similar roles in development processes. In black-grass, GSTFl is known to be in- duced by multiple inputs, which include both biotic (drought, heat) and abiotic (herbicide, safener) treatments. We speculate that in black-grass, biotypes showing elevated levels of expression of genes regulating each of these signaling pathways could be sequentially selected for through a combination of repeated herbicide treatments or adverse weather conditions, effectively ramping up the expression of GSTFl over generations to the point that MHR is invoke
• • This indicates that additional regulatory systems are particularly likely to have evolved to control MHR in annual rye-grass relative to black-grass, which is consistent with the relative greater diversity of resistance mechanisms described in this weed.