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Discovery and Directed Evolution of a Glyphosate Tolerance Gene
Linda A. Castle,1*Daniel L. Siehl,1Rebecca Gorton,1Phillip A. Patten,2Yong Hong Chen,2Sean Bertain,1Hyeon-Je Cho,1Nicholas Duck,3James Wong,3Donglong Liu,3Michael W. Lassner1
The herbicide glyphosate is effectively detoxified by N-acetylation.We screened a collection of microbial isolates and discoveredenzymes exhibiting glyphosate N-acetyltransferase (GAT) activity.Kinetic properties of the discovered enzymes were insufficientto confer glyphosate tolerance to transgenic organisms. Eleveniterations of DNA shuffling improved enzyme efficiency by nearlyfour orders of magnitude from 0.87 mM–1 min–1 to8320 mM–1 min–1. From the fifth iteration and beyond,GAT enzymes conferred increasing glyphosate tolerance to Escherichiacoli, Arabidopsis, tobacco, and maize. Glyphosate acetylationprovides an alternative strategy for supporting glyphosate useon crops.
1 Verdia, Inc. Redwood City, CA 94063, USA. 2 Maxygen Inc., Redwood City, CA 94063, USA. 3 Pioneer Hi-Bred International, Inc., Johnston, IA 50131, USA.
Present address: Athenix Corporation, Research Triangle Park,NC 27709, USA.
* To whom correspondence should be addressed. E-mail: linda.castle{at}verdiainc.com.
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Present address: Athenix Corporation, Research Triangle Park, NC 27709, USA. 
