Weed Employs Gene Amplification to Resist Glyphosate

Weeds have evolved a new form of resistance to the world's most important herbicide, glyphosate, according to research conducted by scientists from the Colorado State University and University of Western Australia. Todd Gaines and colleagues, studying glyphosate-resistant Amaranthus palmeri populations from Georgia, discovered an evolutionary tool employed by Amaranthus to resist the herbicide: gene amplification. Details of their finding appear in the current issue of the Proceedings of the National Academy of Sciences (PNAS).

Glyphosate is toxic because it inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). So far, weeds that are resistant to the herbicide exhibit either a mutated ESPS gene or a trait that inhibits transport of glyphosate within the plant. The finding by Gaines and colleagues presents an entirely different case. The researcher found that the genomes of glyphosate resistant Amaranthus plants contained from 5-fold to more than 160-fold more copies of the EPSPS gene than did genomes of susceptible plants. Massive overproduction of EPSPS produced by the additional EPSPS gene copies allows the plant to cope despite the presence of glyphosate.

In a commentary in the same issue of PNAS, UWA Winthrop Professor and WAHRI Director Stephen Powles, noted that "the potential loss of glyphosate to significant areas of world cropping is a threat to global food production" and to avert "To avert this situation requires that glyphosate be used more judiciously and with more diversity than is currently the case."

The paper published by PNAS is available at http://www.pnas.org/content/early/2009/12/10/0906649107 Read the commentary at http://www.pnas.org/content/107/3/955.full