By Flora Mauch, Checkbiotech

Herbicide tolerance is the most common transgenic crop trait in the world. Its importance might increase in the next years, as researchers discovered a new gene, providing a robust tolerance against glyphosate, one of the most important commercially sold herbicide active ingredients.

Glyphosate is the active ingredient in the herbicides Roundup from Monsanto and Touchdown by Syngenta. Generally, it is toxic to all kinds of weeds and crops. Thus for a long time, it was not possible to use it in agriculture. Only since glyphosate tolerant crops have been developed with the help of genetic engineering, has glyphosate been frequently used to increase crop yields. 80% of the U.S. market in soybeans and cotton are now plants that tolerate glyphosate.

The way glyphosate operates, is it inhibits the synthesis of essential aromatic amino acids. Under these conditions, plants are not able to survive. However, there is a similar enzyme in some microorganisms that does the same work, but is not affected by glyphosate. Researchers took this into account and inserted the resistant enzyme’s gene into crop plants. Thus, desired plants can even survive in the presence of high concentrations of herbicide. Regrettably, glyphosate remains in the plant and accumulates. In this way, it might interfere with reproductive development and may lower crop yield if plants are sprayed late in development.

Seeing this disadvantage, researchers from Pioneer Hi-Bred, International and Verdia Inc. in Redwood City searched for a method to detoxify glyphosate. One solution was to let an enzyme called glyphosate N-acetyltransferase (GAT) carry out the process. GAT modifies glyphosate and turns it into N-acetylglyphosate that is indeed stable as well, but no longer herbicidal.

With the process of DNA shuffling, the team obtained an enzyme that had a nearly 10,000-fold improvement over the parental enzyme. The improved enzyme confers glyphosate tolerance to corn plants in the field.

Before these plants will be brought out on the market, it will take at least five years, Dr Castle explained because, “It takes years to test trait efficacy in the field, convert the trait into elite varieties, and to assemble product safety data for the U.S. regulatory agencies. Pioneer Hi-Bred is evaluating corn plants now and the joint venture between Verdia and Delta and Pine Land is evaluating the trait in cotton.”

According to reports, Verdia Inc. also has projects underway in the areas of insect, herbicide and disease resistance. Probably we will hear a lot more in the future.

Flora Mauch is a Science Writer for Checkbiotech in Basel, Switzerland and is currently studying Biology.