HAU16008-06-2 - Plant Protection Traits Lecture 6 Monday...

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1 Plant Protection Traits Lecture 6 Monday November 03, 2008 Herbicide Tolerance Core Concepts : Infinite germplasm Single dominant genes Chemical herbicide selectivity Tolerance vs detoxification 1. Well defined mode of action 2. Defined specific target, typically one step in an essential pathway binding to one site of the target protein 3. Lethal consequences that are reversible by adding the end product 4. Selective toxicity with low mammalian toxicity
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2 Glyphosate tolerance. 1. Molecular target 2. Mode of action 3. Strategies for herbicide tolerance 4. Altered target - Bacterial EPSP synthase 5. Over expression of plant EPSP synthase 6. Chloroplast targeting 7. Expression in the meristem Bacterial EPSP synthase from a bacterial aro A mutant Over Expression : Over expression of the target protein by either introducing another copy of the gene or altering the expression. This provides more target than the herbicide can bind, thus, keeping the pathway functional. Weak resistance is typically observed with this approach. Three mechanisms of resistance to herbicides: Altered Target : Alterations in the target enzyme such that it prevents the binding of the herbicide. The consequences of this could; affect the binding of the natural substrate if there is an overlap of the binding sites; Alterations in catalytic efficiency of the target enzyme/protein could occur. Detoxification : Introduction of a gene that breaks down or chemically alters the herbicide molecule such that it is rendered inactive. For this approach to work it is important that; it should involve a single gene; should not require complex cofactors to function in the plant cell; should exhibit suitable kinetic properties/parameters; should produce metabolites that have little or no toxicity to the plant cell and it should be highly specific so that other plant metabolites are not recognized
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3 Targetting amino acid biosynthesis: Essential amino acids : His, Isoleu, Phe, Thr, Leu, Met, Lys, Trp [9] Non Esential : Glu, Gln, Asp, Asn, Ala, Pro, Tyr, Cys, Gly [11] Herbicides inhibiting photosynthesis. Atrazine Tolerance to bromoxynil Detoxification/degradation approach
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4 Detox Mechanisms: Preferably a single gene. No complex cofactors to function in the plant cell. Suitable kinetic properties/parameters. Should produce metabolites that have little or no toxicity to the plant cell. Should be highly specific so that other plant metabolites are not recognized. Directed Evolution of a Glyphosate Tolerance Gene Castle et al., 2004 Castle et al., 2004
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5 Annual cost of weed control in the US is in excess of $5 billion. Herbicides are designed to kill plants and not other living things. Their utility is dependent upon the nature of the weeds, cost of treatment, value of the crop, its sensitivity to weed pressure and labor costs. Herbicides have a well designed mode of action. They are very specific: target one step of a metabolic
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This note was uploaded on 12/03/2010 for the course ECONOMY Eco 100 taught by Professor Taidat during the Spring '10 term at Hanoi University of Technology.

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HAU16008-06-2 - Plant Protection Traits Lecture 6 Monday...

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