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

BACKGROUND: Glyphosate‐resistant goosegrass has recently evolved and is homozygous for the double mutant of EPSPS (T(102)I, P(106)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‐T(102)I, P(106)A (TIPA K (i) = 150 μM) to determine the resistance magnitude for a more potent variant EPSPS that might evolve in weeds. RESULTS: Transgenic A. thaliana plants, homozygous for one, two or four copies of AtEPSPS‐TIPA, had resistance (IC(50) 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. CONCLUSIONS: 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.