What We Have Learned from Atrazine – the Herbicide That Launched 1000 Careers.

Since its introduction into the environment in the 1950s, atrazine has become one of the most widely studies herbicides. The widespread use of atrazine and other s-triazine herbicides to control weeds in agricultural production fields has impacted surface and groundwater in the United States and elsewhere. Since its inception, the biodegradation of s-triazine herbicides has been widely studied, with reports of varying results and suggested sorption and degradation pathways. We previously reported the cloning, sequencing, and expression of six genes involved in the atrazine biodegradation pathway by Pseudomonas sp. strain ADP, which is initiated by atzA, encoding atrazine chlorohydrolase. This pathway appears to be the dominant one by which bacteria obtain N from this herbicide. Here we explored the use of enhanced expression of a modified bacterial atrazine chlorohydrolase, p-AtzA, in transgenic grasses (tall fescue, perennial ryegrass, and switchgrass) and the legume alfalfa for the biodegradation of atrazine. Enhanced expression of p-AtzA was obtained by using combinations of the badnavirus promoter, the maize alcohol dehydrogenase first intron, and the maize ubiquitin promoter. For alfalfa, we used the first intron of the 5'-untranslated region tobacco alcohol dehydrogenase gene and the cassava vein mosaic virus promoter. Resistance of plants to atrazine was correlated with in vivo levels of gene expression and atrazine degradation. The in planta expression of p-atzA enabled transgenic tall fescue to transform atrazine into hydroxyatrazine and other metabolites. Results of our studies highlight the potential use of transgenic plants for bioremediating atrazine in the environment.