Messenger RNA encoding a glutathione-S-transferase responsible for herbicide tolerance in maize is induced in response to safener treatment.

Glutathione-S-transferases (GST's) in maize represent a family of enzymes which conjugate glutathione to several major classes of pre-emergent, selective herbicides. Chemicals termed safeners have been demonstrated to increase the tolerance of maize toward such herbicides when the maize seed has been previously treated with safeners. It has subsequently been shown that corresponding increases in glutathione-S-transferase species occur. To determine whether these compounds act at a transcriptional level we have used synthetic oligonucleotide probes to isolate cDNA clones encoding the major GST polypeptide subunit, designated GST A. The identity of the clones has been confirmed by hybrid-selected mRNA translation and immunoprecipitation using antibodies made against this GST species as well as by production of active GST in yeast cells transformed with an expression vector containing the cloned DNA. GST A has been found to be encoded in a mRNA of 1.1 kb. Sequencing of cDNA products obtained by primer extension of maize mRNA using our oligonucleotide probes is consistent with this mRNA corresponding to the isolated cDNA clone. Using the clone as a probe for Northern analysis we have found a three to four-fold increase in the steady state level of this mRNA in maize tissue grown from safener-treated seeds. The level of safener which gives this induction is comparable to that required to obtain herbicide tolerance in the field.