DETOX LETS CROPS TAKE HERBICIDE | May 24, 2004 Issue - Vol. 82 Issue 21 | Chemical & Engineering News
Volume 82 Issue 21 | p. 10 | News of The Week
Issue Date: May 24, 2004

DETOX LETS CROPS TAKE HERBICIDE

Thanks to an evolved enzyme, engineered crops tolerate glyphosate
Department: Science & Technology
FIELD OF DREAMS
Corn containing Verdia's optimized glyphosate-detoxifying enzyme grows in Hawaii, having survived exposure to the herbicide.
Credit: COURTESY OF JEFF DERRY AND WAYNE MEHRE/PIONEER HI-BRED
8221notw2fields1
 
FIELD OF DREAMS
Corn containing Verdia's optimized glyphosate-detoxifying enzyme grows in Hawaii, having survived exposure to the herbicide.
Credit: COURTESY OF JEFF DERRY AND WAYNE MEHRE/PIONEER HI-BRED

Crops engineered to make an enzyme capable of N-acetylating the widely used, environmentally friendly herbicide glyphosate--a modification that renders glyphosate nontoxic--are resistant to the weed killer, according to a new study. If commercialized, this novel strategy could spark competition and further innovation in the lucrative market for glyphosate-tolerant crops, worth nearly $2.2 billion in 2002.

The world's top-selling herbicide, glyphosate--originally trademarked by Monsanto as Roundup--kills weeds by inhibiting an enzyme that plants rely on to biosynthesize the aromatic amino acids they require for growth. Glyphosate is widely used in combination with Monsanto-brand Roundup Ready crops, which are engineered to contain a glyphosate-immune microbial version of this enzyme. This allows farmers to spray entire fields with the herbicide, killing the weeds but not their crops.

DETOX
Verdia's optimized enzyme uses the acetyl donor acetyl coenzyme A to convert the herbicide glyphosate into nontoxic N-acetylglyphosate.
Credit: SCIENCE © 2004
8221notw2aa_ce
 
DETOX
Verdia's optimized enzyme uses the acetyl donor acetyl coenzyme A to convert the herbicide glyphosate into nontoxic N-acetylglyphosate.
Credit: SCIENCE © 2004

Now, plant scientist Linda A. Castle of Redwood City, Calif.-based Verdia and her colleagues at Verdia and Pioneer Hi-Bred of Johnston, Iowa, have developed what they believe is a promising alternative strategy for creating glyphosate-tolerant crops [Science, 304, 1151 (2004)]. Instead of relying on an enzyme that isn't susceptible to glyphosate inhibition, Castle's team created transgenic plants that can cleanse themselves of glyphosate by turning the herbicide into N-acetylglyphosate, which is harmless to the plant.

Castle's team screened only a few hundred common microbes before unearthing a family of enzymes from a soil bacterium capable of weakly catalyzing glyphosate acetylation. They then fragmented and recombined these enzymes' genetic sequences to create a better performing variant. After repeating this DNA shuffling process nearly a dozen times--and even including some additional genetic diversity from different but related microbial nzymes--the team managed to create a glyphosate N-acetyltransferase that's nearly 10,000 times more efficient than the original enzymes. Corn containing this optimized enzyme survives glyphosate applications six times the normal dose, Castle says.

Initial data suggest that although N-acetylglyphosate sticks around in these plants, it is no more toxic to the environment than glyphosate, she adds. Stephen O. Duke of USDA's Agricultural Research Service predicts, "Provided no toxicological problems are found with this metabolite, this achievement has good potential for commercial success." Verdia is currently evaluating the commercial potential of the trait in both corn and cotton, but products are still years off, Castle notes.

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society

Leave A Comment

*Required to comment