Detoxified!

scientists have engineered plants capable of detoxifying lethal doses of the widely used herbicide glyphosate. Commercialisation of this trait will challenge biotech giant Monsanto's dominance of the genetically modified crop market. Monsanto markets glyphosate under the brand name 'Roundup'; the company also sells crops engineered to resist the herbicide.

Normally, when sprayed on a large scale, glyphosate inhibits the function of a key plant enzyme that helps make amino acids. Therefore, Monsanto engineered resistance by adding the gene for a similar microbial enzyme that isn't affected. But traces of the herbicide remain in the modified plants. This interferes with the reproductive development of the crops, reducing their yields.

To find another way to protect the plants, researchers of us-based Verdia Incorporation, Maxygen Incorporation and Pioneer Hi-Bred International Incorporation took their cue from a technology wherein a microbial enzyme is used to modify the herbicide glufosinate.

The researchers searched their microbial collection to find a similar enzyme for glyphosate. In 2000, they found glyphosate n-acetyltransferase (gat) enzymes in Bacillus licheniformis. The enzymes had weak glyphosate detoxifying capabilities. Therefore, the gene variants encoding the gat enzymes were isolated for use in a 'dna shuffling' process. The researchers selected the gene variants that encoded the most active gat enzymes. After 11 generations of recombination, they created enzymes that are nearly 10,000 times more active than the original parents (Science, Vol 304, No 5674, May 21, 2004).

The potential of the enzymes was tested in corn plants. The crop tolerated six times the concentration of glyphosate than what is normally applied, with no effect on the yield. According to Linda Castle, one of the researchers, gat should work in other crops as well. It will take at least five years to commercialise the technology.