title: Mechanism of resistance of evolved glyphosate-resistant Palmer amaranth (Amaranthus palmeri).
abstract: Evolved glyphosate resistance in weedy species represents a challenge for the continued success and utility of glyphosate-resistant crops. Glyphosate functions by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). The resistance mechanism was determined in a population of glyphosate-resistant Palmer amaranth from Georgia (U.S.). Within this population, glyphosate resistance correlates with increases in (a) genomic copy number of EPSPS, (b) expression of the EPSPS transcript, (c) EPSPS protein level, and (d) EPSPS enzymatic activity. Dose response results from the resistant and an F(2) population suggest that between 30 and 50 EPSPS genomic copies are necessary to survive glyphosate rates between 0.5 and 1.0 kg ha(-1). These results further confirm the role of EPSPS gene amplification in conferring glyphosate resistance in this population of Palmer amaranth. Questions remain related to how the EPSPS amplification initially occurred and the occurrence of this mechanism in other Palmer amaranth populations and other glyphosate-resistant species.
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University, 1177 Campus Delivery, Fort Collins, Colorado 80523, USA. todd.gaines@uwa.edu.au
authors.forename: Todd A
authors.initials: TA
authors.lastname: Gaines
authors.forename: Dale L
authors.initials: DL
authors.lastname: Shaner
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Ward
authors.forename: Jan E
authors.initials: JE
authors.lastname: Leach
authors.forename: Christopher
authors.initials: C
authors.lastname: Preston
authors.forename: Philip
authors.initials: P
authors.lastname: Westra
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D027721:Amaranthus / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018628:Gene Dosage; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D057685:Plant Weeds / Q000187:drug effects*; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D004791:Enzyme Inhibitors; D005998:Glycine; D006540:Herbicides; D010940:Plant Proteins; D000097797:Glyphosate