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Published January 1, 2010 | Version v1
Journal article Open

Gene amplification confers glyphosate resistance in Amaranthus palmeri

Creators

  • 1. Colorado State Univ, Dept Bioagr Sci & Pest Management, Ft Collins, CO 80523 USA
  • 2. Univ Wisconsin, Dept Hort, Madison, WI 53706 USA
  • 3. Monsanto Co, St Louis, MO 63167 USA
  • 4. ARS, Water Management Res Unit, USDA, Ft Collins, CO 80526 USA
  • 5. Univ Illinois, Dept Crop Sci, Urbana, IL 61801 USA
  • 6. Univ Georgia, Dept Crop & Soil Sci, Tifton, GA 31794 USA
  • 7. ARS, Crop Protect & Management Res Unit, USDA, Tifton, GA 31794 USA
  • 8. Univ Georgia, Dept Crop & Soil Sci, Athens, GA 30602 USA
  • 9. Univ Adelaide, Sch Agr Food & Wine, Glen Osmond, SA 5064, Australia

Description

The herbicide glyphosate became widely used in the United States and other parts of the world after the commercialization of glyphosate-resistant crops. These crops have constitutive overexpression of a glyphosate-insensitive form of the herbicide target site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Increased use of glyphosate over multiple years imposes selective genetic pressure on weed populations. We investigated recently discovered glyphosate-resistant Amaranthus palmeri populations from Georgia, in comparison with normally sensitive populations. EPSPS enzyme activity from resistant and susceptible plants was equally inhibited by glyphosate, which led us to use quantitative PCR to measure relative copy numbers of the EPSPS gene. Genomes of resistant plants contained from 5-fold to more than 160-fold more copies of the EPSPS gene than did genomes of susceptible plants. Quantitative RT-PCR on cDNA revealed that EPSPS expression was positively correlated with genomic EPSPS relative copy number. Immunoblot analyses showed that increased EPSPS protein level also correlated with EPSPS genomic copy number. EPSPS gene amplification was heritable, correlated with resistance in pseudo-F-2 populations, and is proposed to be the molecular basis of glyphosate resistance. FISH revealed that EPSPS genes were present on every chromosome and, therefore, gene amplification was likely not caused by unequal chromosome crossing over. This occurrence of gene amplification as an herbicide resistance mechanism in a naturally occurring weed population is particularly significant because it could threaten the sustainable use of glyphosate-resistant crop technology.

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