A double EPSPS gene mutation endowing glyphosate resistance shows a remarkably high resistance cost

A novel glyphosate resistance double point mutation (T102I/P106S, TIPS) in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene has been recently identified for the first time only in the weed species Eleusine indica. Quantification of plant resistance cost associated with the TIPS and the often reported glyphosate resistance single P106S mutation was performed. A significant resistance cost (50% in seed number currency) associated with the homozygous TIPS but not the homozygous P106S EPSPS variant was identified in E.indica plants. The resistance cost associated with the TIPS mutation escalated to 85% in plants under resource competition with rice crops. The resistance cost was not detected in nonhomozygous TIPS plants denoting the recessive nature of the cost associated with the TIPS allele. An excess of 11-fold more shikimate and sixfold more quinate in the shikimate pathway was detected in TIPS plants in the absence of glyphosate treatment compared to wild type, whereas no changes in these compounds were observed in P106S plants when compared to wild type. TIPS plants show altered metabolite levels in several other metabolic pathways that may account for the expression of the observed resistance cost. In a novel evolutionary event, a double point mutation (TIPS) in the EPSPS gene has been shown to endow high levels of glyphosate resistance in Eleusine indica. However, in the absence of glyphosate treatment, plants carrying the glyphosate resistance EPSPS TIPS mutation exhibit profound ecophysiological changes leading to a remarkably fitness cost. We present empirical results that summarize the TIPS plant traits associated with the fitness cost in comparison with wild type and plants carrying only a single point mutation (Pro-106-Ser) in the EPSPS gene.