Biochemical characterization of metabolism‐based atrazine resistance in <i>Amaranthus tuberculatus</i> and identification of an expressed <i><scp>GST</scp></i> associated with resistance

Abstract

Summary Rapid detoxification of atrazine in naturally tolerant crops such as maize ( Zea mays ) and grain sorghum ( Sorghum bicolor ) results from glutathione S ‐transferase ( GST ) activity. In previous research, two atrazine‐resistant waterhemp ( Amaranthus tuberculatus ) populations from Illinois, U.S.A. (designated ACR and MCR ), displayed rapid formation of atrazine‐glutathione ( GSH ) conjugates, implicating elevated rates of metabolism as the resistance mechanism. Our main objective was to utilize protein purification combined with qualitative proteomics to investigate the hypothesis that enhanced atrazine detoxification, catalysed by distinct GST s, confers resistance in ACR and MCR . Additionally, candidate Atu GST expression was analysed in an F 2 population segregating for atrazine resistance. ACR and MCR showed higher specific activities towards atrazine in partially purified ammonium sulphate and GSH affinity‐purified fractions compared to an atrazine‐sensitive population ( WCS ). One‐dimensional electrophoresis of these fractions displayed an approximate 26‐ kD a band, typical of GST subunits. Several phi‐ and tau‐class GST s were identified by LC ‐ MS / MS from each population, based on peptide similarity with GST s from Arabidopsis . Elevated constitutive expression of one phi‐class GST , named Atu GSTF 2 , correlated strongly with atrazine resistance in ACR and MCR and segregating F 2 population. These results indicate that Atu GSTF 2 may be linked to a metabolic mechanism that confers atrazine resistance in ACR and MCR .