Herbicide resistance engineering

Friesen, L.F., Nelson, A.G. and Van Acker, R.C. (2003). Evidence of contamination of pedigreed canola (Brassica napus) seedlots in western Canada with genetically engineered herbicide resistance traits . Agron J, 95, 1342-1347. 

N.R., Thompson, C., Vanmontagu, M., and Leemans, J. 1987. Engineering herbicide resistance in plants by expression of a detoxifying enzyme. EMBO... 

Herbicides are classified as either selective or broad spectrum. Selective herbicides can be used in-crop to control weeds without significant crop damage. Broad spectrum herbicides such as glyphosate and glufosinate are limited to preplant or post-directed applications. The technology to engineer herbicide resistance has enabled in-crop use of broad spectrum herbicides for improved weed control and yield. 

The development of herbicides that inhibit photosynthetic electron transport has proved to be outstandingly successful. Furthermore, because of the efficiency of these compounds and their use as tools to study photosynthesis, our knowledge of photosystem II in particular has been greatly enhanced by their use. Recent developments involving X-ray structural analysis of photosynthetic bacterial reaction centers as well as the ability to engineer herbicide resistance into crop plants have been outstanding scientific achievements. 

The EPA is involved in the regulation process if the transgenic plant expresses a pest- or herbicide-resistant engineered trait in addition to a biopharmaceutical. 

Another major application of herbicide resistance is its utility as a selectable marker. Like antibiotic resistance in bacterial transformation, herbicide resistance should prove extremely useful for selecting transformants that are insect resistant, disease resistant, or engineered for other non-selectable traits. Many of these herbicide resistant markers have already been integrated into plant cloning vectors (32.43). 

One food safety concern about genetic engineering is that toxic components naturally found might be increased. Attempts to breed or genetically engineer plants with natural herbicides or pesticides or herbicide-resistant plants could increase the potential toxicity if many foods would carry a natural pesticide. Scientists must not be lured into the common belief that nature is benign and chemicals from the lab are noxious. 

The risk of passing resistance genes from a crop to a wild related species is not inconceivable. A number of crops, (e.g., rice, millets, sorghum, oats, rapeseed, sugar beets, sunflower, alfalfa, peas, and potatoes) could be involved in introgression. Therefore, as herbicide resistant crops are engineered, a genetic barrier between crops and weeds must be devised. 

Many of the characteristics which combine to make ALS an excellent target for engineering beneficial herbicide resistance in crop plants may also lead to the proliferation of herbicide-resistant weeds. These characteristics include the following sulfonylurea herbicide resistance is a semi-dominant trait that is carried on a nuclear gene(s) ALS is the single primary site of action there are multiple positions in ALS that can be mutated to confer herbicide resistance mutant ALS enzymes can possess full catalytic activity. The latter property results in engineered crop plants that are fit, but can equally well result in weed biotypes that are fit. 

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