Identification and expression pattern of a glutathione S-transferase in Echinochloa crus-galli

Plant glutathione S-transferase (GST) forms a major part of the herbicide detoxification enzyme network in plants. A GST cDNA was isolated from Echinochloa crus-galli and characterised. The gene, designated EcGST1 (E.crus-galli GeneBank no: ), has a 684bp open reading frame predicted to encode a 25kD protein. Sequence alignment showed that EcGST1 is a GST homologue. Its expression in response to quinclorac treatment was monitored in seedlings (leaves and roots) and adult plants (leaves, roots, stems and seeds) of quinclorac-resistant (R) and susceptible (S) biotypes of E.crus-galli. EcGST1 expression was 1.5-3 times greater in the R plants than in the S plants. However, after exposure to quinclorac, the difference in the expression levels of EcGST1 in R plants, compared with S plants, increased to a ratio of 6-10. Enhanced EcGST1 levels should enable greater quinclorac detoxification following quinclorac stimulation in R plants. GST-based metabolism may be partially responsible for resistance to quinclorac in E.crus-galli. The results suggest a new resistance mechanism for this R biotype in Chinese rice fields.