A role for glutathione transferases functioning as glutathione peroxidases in resistance to multiple herbicides in black-grass.
Black-grass (Alopecurus myosuroides) is a major weed of wheat in Europe, with several populations having acquired resistance to multiple herbicides of differing modes of action. As compared with herbicide-susceptible black-grass, populations showing herbicide cross-resistance contained greatly elevated levels of a specific type I glutathione transferase (GST), termed AmGST2, but similar levels of a type III GST termed AmGST1. Following cloning and expression of the respective cDNAs, AmGST2 differed from AmGST1 in showing limited activity in detoxifying herbicides but high activities as a glutathione peroxidase (GPOX) capable of reducing organic hydroperoxides. In contrast to AmGST2, other GPOXs were not enhanced in the herbicide-resistant populations. Treatment with a range of herbicides used to control grass weeds in wheat resulted in increased levels of hydroperoxides in herbicide-susceptible populations but not in herbicide-resistant plants, consistent with AmGST2 functioning to prevent oxidative injury caused as a primary or secondary effect of herbicide action. Increased AmGST2 expression in black-grass was associated with partial tolerance to the peroxidizing herbicide paraquat. The selective enhancement of AmGST2 expression resulted from a constitutively high expression of the respective gene, which was activated in herbicide-susceptible black-grass in response to herbicide safeners, dehydration and chemical treatments imposing oxidative stress. Our results provide strong evidence that GSTs can contribute to resistance to multiple herbicides by playing a role in oxidative stress tolerance in addition to detoxifying herbicides by catalysing their conjugation with glutathione.
Cummins
I
I
Department of Biological Sciences, University of Durham, UK.
Cole
D J
DJ
Edwards
R
R
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D018432:Drug Resistance, Multiple; D015870:Gene Expression; D017343:Genes, Plant; D005979:Glutathione Peroxidase / Q000235:genetics / Q000378:metabolism*; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism*; D006540:Herbicides / Q000494:pharmacology; D008969:Molecular Sequence Data; D018384:Oxidative Stress; D006109:Poaceae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D017386:Sequence Homology, Amino Acid
D006540:Herbicides; D005979:Glutathione Peroxidase; D005982:Glutathione Transferase