Glutamine synthetase mutation conferring target‐site‐based resistance to glufosinate in soybean cell selections

Abstract

Glufosinate-resistant soybean cells were achieved through direct selection of diploid cells in the suspension culture. Here, the mutations in the glutamine synthetase (GS) gene are described to understand the evidence pointing to the functional role of the GS gene in the herbicide sensitivity of the mutant cells. Based on the I(50) values, dose-response experiments at the cell level showed that the resistance ratio of the resistant cell was 50-fold, whereas the in vitro inhibition of GS activity required a 4.56-fold greater concentration of glufosinate in the resistant cell than in the untreated control. Comparison of the nucleotide sequences identified nine point differences in the GS gene between the resistant and untreated cells, leading to eight amino acid substitutions in the deduced polypeptide sequence. Northern hybridization of the GS mRNA showed that the accumulation of GS gene mRNA transcript in resistant cells was higher than that in the untreated cells. Changes in sensitivity to glufosinate have been related to mutations at the binding site of the herbicide on the glutamine synthetase. His(249) is one of the residues implicated in the binding domain for the substrate and inhibitor, and hence the exchange of this residue with tyrosine plays a role in lowering the sensitivity of the mutated enzyme.