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

Abstract

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.

Re-registration Challenges of Glyphosate in the European Union

“…As for emerging plant resistance against glyphosate, glyphosate itself and glyphosate-based herbicides have been shown to affect the disease resistance and health of plants by undermining their innate physiological defenses in mechanisms related to the mode of action of glyphosate, even in crops engineered for glyphosate-tolerance, and by interferences with the local microbial ecology in the rhizosphere (Martinez et al, 2018). The evolution of resistance was shown to occur due to gene amplification (Chen et al, 2017;Dolatabadian et al, 2017;Fernandez-Escalada et al, 2017;Han et al, 2017;Jugulam and Gill, 2018). Epigenetic alterations through increased levels of DNA and histone methylation were identified in response to exposure to glyphosate (Nardemir et al, 2015;Kim et al, 2017;Margaritopoulou et al, 2018;Markus et al, 2018).…”

A novel TIPT double mutation in EPSPS conferring glyphosate resistance in tetraploid Bidens subalternans

“…A similar double mutation, TIPS (Thr102Ile and Pro106Ser), has been reported in E. indica and B. pilosa . E. indica plants homozygous for the TIPS mutation are highly resistant to glyphosate, but also display the strong fitness cost associated with it . Therefore, most of the TIPS mutant E. indica plants in nature tend to disappear under low glyphosate selection pressure or occur as heterozygous plants due to the fitness cost associated with the TIPS resistance allele .…”

“…In E. indica , single Pro106 and double TIPS mutants can coexist in the population and their proportion may vary depending on the levels of glyphosate selection pressure. Additionally, the Thr102Ile mutation may have evolved more recently from previous Pro106Ser single mutant plants . The absence of Pro106 single mutants within 30 GR B. subalternans individuals may suggest that these plants have been under intense glyphosate selection pressure, leading to the extinction of single mutant genotype.…”

“…The first case of an EPSPS TIPS double mutation evolved in a weedy species was documented in diploid Eleusine indica highly resistant to glyphosate (> 180‐fold) . In addition to providing high GR levels, the TIPS mutation also imparts a remarkably high fitness cost for homozygous plants . We report a different EPSPS double amino acid substitution – Thr102Ile and Pro106Thr (TIPT), conferring high level of glyphosate resistance in the tetraploid B. subalternans .…”

EPSPS duplication and mutation involved in glyphosate resistance in the allotetraploid weed species Poa annua L.

“…At the whole‐plant level, SNPs at position 106 commonly confer variable levels of resistance in the order of three‐ to nine‐fold compared to susceptible biotypes . Conversely, double amino acid mutations at position 102 and 106 may confer resistance levels up to 180‐fold, commonly accompanied by high fitness costs …”