Evaluation of glyphosate resistance in Arabidopsis thaliana expressing an altered target site EPSPS

Glyphosate-resistant goosegrass has recently evolved and is homozygous for the double mutant of EPSPS (T₁₀₂ I, P₁₀₆ S or TIPS). These same mutations combined with EPSPS overexpression, have been used to create transgenic glyphosate-resistant crops. Arabidopsis thaliana (Wt EPSPS K_i ∼ 0.5 μM) was engineered to express a variant AtEPSPS-T₁₀₂ I, P₁₀₆ A (TIPA K_i = 150 μM) to determine the resistance magnitude for a more potent variant EPSPS that might evolve in weeds.

Transgenic A. thaliana plants, homozygous for one, two or four copies of AtEPSPS-TIPA, had resistance (IC₅₀ values, R/S) as measured by seed production ranging from 4.3- to 16-fold. Plants treated in reproductive stage were male sterile with a range of R/S from 10.1- to 40.6-fold. A significant hormesis (∼ 63% gain in fresh weight) was observed for all genotypes when treated at the initiation of reproductive stage with 0.013 kg ha^-1 . AtEPSPS-TIPA enzyme activity was proportional to copy number and correlated with resistance magnitude.

A. thaliana, as a model weed expressing one copy of AtEPSPS-TIPA (300-fold more resistant), had only 4.3-fold resistance to glyphosate for seed production. Resistance behaved as a single dominant allele. Vegetative tissue resistance was 4.7-fold greater than reproductive tissue resistance and was linear with gene copy number. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.