title: Concerted action of target-site mutations and high EPSPS activity in glyphosate-resistant junglerice (Echinochloa colona) from California.
abstract: BACKGROUND
  Echinochloa colona is an annual weed affecting field crops and orchards in California. An E. colona population carrying a mutation in the EPSPS gene endowing resistance to glyphosate, the most widely used non-selective herbicide, was recently identified in the Northern Sacramento Valley of California. Plants from this population, from a suspected glyphosate-resistant (GR) population, and from one susceptible (S) population collected in the Northern Sacramento Valley of California, were used to generate three GR and one S selfed lines to study possible mechanisms involved in glyphosate resistance.
  
  
  RESULTS
  Based on the amount of glyphosate required to kill 50% of the plants (LD50 ), GR lines were 4-9-fold more resistant than S plants and accumulated less shikimate after glyphosate treatment. GR and S lines did not differ in glyphosate absorption, translocation or metabolism. A different target-site mutation was found in each of two of the GR lines corresponding to Pro106Thr and Pro106Ser substitutions; the mutations were found in different homoeologous EPSPS genes. No mutation was found in the third GR line, which exhibited 1.4-fold higher basal EPSPS activity and a fivefold greater LD50 than S plants. Quantitative RT-PCR revealed that GR lines had similar or lower EPSPS expression than S plants.
  
  
  CONCLUSIONS
  It is demonstrated that individuals with different glyphosate resistance mechanisms can coexist in the same population, individuals from different populations may carry different resistance mechanisms and different mechanisms can act in concert within single E. colona plants. However, other plant factors or resistance mechanisms appear to modulate plant expression of EPSPS sensitivity to glyphosate.
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA, USA.
authors.forename: Rocío
authors.initials: R
authors.lastname: Alarcón-Reverte
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA, USA.
authors.forename: Alejandro
authors.initials: A
authors.lastname: García
authors.affiliation: Natural Products Utilization Research Unit, USDA-ARS, University, MS, USA.
authors.forename: Susan B
authors.initials: SB
authors.lastname: Watson
authors.affiliation: Department of Pesticides, Faculty of Agriculture, University of Cairo, Giza, Egypt.
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Abdallah
authors.affiliation: Estación Experimental Agroindustrial 'Obispo Colombres', Tucumán, Argentina.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Sabaté
authors.affiliation: Departmento de Ciencias Vegetales, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: María J
authors.initials: MJ
authors.lastname: Hernández
authors.affiliation: Natural Products Utilization Research Unit, USDA-ARS, University, MS, USA.
authors.forename: Franck E
authors.initials: FE
authors.lastname: Dayan
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA, USA.
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Fischer
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase / Q000235:genetics; D002140:California; D031747:Echinochloa / Q000235:genetics*; D014644:Genetic Variation; D005998:Glycine / Q000031:analogs & derivatives*; D053209:Herbicide Resistance / Q000235:genetics*; D006540:Herbicides; D009154:Mutation; D057685:Plant Weeds / Q000235:genetics*; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D005998:Glycine; D006540:Herbicides; D000097797:Glyphosate
keywords: 5-enolpyruvylshikimate-3-phosphate synthase; EPSPS expression; EPSPS inhibition assay; polyploidy; resistance mechanism