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Development of Crop Plants - History• Domestication of crops• We have been modifying our crops
for 10,000 years through Selection.• All crops we grow today have
undergone extensive genetic change from their wild ancestors.
• Crops, strains and genes have moved around the globe.
Teosinte Hybrids Modern Corn
Teosinte Hybrids Modern Corn
Domestication ofcorn creating a new species in the process – Zea mays
Domestication ofcorn creating a new species in the process – Zea mays
Thanks to C.S. Prakash for some of the pictures on this and the next couple of slides.
The domestication of animals has also been accompanied by extensive human-directed genetic modification. This is exemplified with the domestic dog, Canis familiaris.
Modern genetics including genomics indicates that all domestic dogs are originally derived from the wolf, Canis lupus. Thus the Siberian Husky and Mexican Chihuahua are derived from the same original specie with the only difference being the extent of the genetic modification!
Traditional Breeding
Crossing individuals with desirablecharacteristics (e.g. yield) and selecting among the progeny. Genes recombine in a randomfashion and finding superior progeny has been as much art as science. Needs excellent management since it’s a numbers game and genotype often masked by environmental influences.
Traditional Breeding
Crossing individuals with desirablecharacteristics (e.g. yield) and selecting among the progeny. Genes recombine in a randomfashion and finding superior progeny has been as much art as science. Needs excellent management since it’s a numbers game and genotype often masked by environmental influences.
For specific characteristics such as fatty acid % of oil, naturally occurring mutants screened for and if not found induced by chemical mutagenesis or irradiation.
For specific characteristics such as fatty acid % of oil, naturally occurring mutants screened for and if not found induced by chemical mutagenesis or irradiation.
Conventional:
Wide Hybridization introduces 20,000 to 100,000 potentially negative genes in order to obtain one desirable disease resistance gene. Induced mutagenesis has been used for decades to creategenetic variants.
Genetic Engineering:Introduce one (or a few) foreign “good” genes into the best accepted cultivar background.
Genetic Engineering:Introduce one (or a few) foreign “good” genes into the best accepted cultivar background.The main thing that is new with genetic engineering is that species barriers can now readily be bridged.
Genetic Engineering:Introduce one (or a few) foreign “good” genes into the best accepted cultivar background.The main thing that is new with genetic engineering is that species barriers can now readily be bridged.This opens new opportunities and depending on how it is used requires
new safeguards.
Recombinant DNA?
Agrobacteriumtumefaciens
A. tumefaciens
Chromosome
T-DNA
Ti plasmid
T-DNA
ChromosomalDNA
CrownGall
Plant crown gall tissue naturally transgenic
Plant chromosomescontaining T-DNA
How Do You Introduce a Foreign Gene into
a Recipient Organism?
Overview
Methods Used to Date for Plant Transformation
Agrobacterium tumefaciens and rhizogenesGene Gun Microprojectiles (PDS)
Electroporation of protoplastsMicroinjectionPollen Tube PathwaySilica Carbide fibersMicrolaser
Viruses [some native genes replaced]
plasmid Desired DNA
Recombinantplasmid Agrobacterium
tumefaciens containing WtTi plasmid
A. tumefaciens containingengineered Ti plasmid
Plant cellinoculated withA. tumefaciens
Plant cell containing Desired DNA
Cultured plant cells
Regenerant
Adult plant expressingdesired trait (DNA)
Inserting foreign genes into plant cells. A plasmid containing DNA is cut with a restriction enzyme & DNA of desired gene (red) inserted. Desired gene then inserted into Ti (tumor-inducing) plasmid naturally found in A. tumefaciens. Plant cell inoculated with A. tumefaciens containing engineered Ti plasmid + the desired DNA transfers desired DNA + t-DNA into plant chromosomes. Plantlets with desired trait then regenerated.
The Gene Gun
PDS1000 Microparticle Delivery System
Helium chamber
Rupture disk
Macrocarrier
DNA coated gold particle
Stopping screen
Focusing device
Target tissue
Gene gunFrom Collins lab
Biolistic Transformation
Before impact
DNA coated gold particle
After impact
During impact
?
Plant Cell Wall
How do Genes do Their Job?
GENE EXPRESSION
DNA
Transcription
mRNA
Translation
Protein
Product A Product B
Structural Gene
Enzyme (Protein)
Roundup Ready Crops
Monsanto web page:
C
O-
O
OH
OH
O
Pi
C
O-
O
O
OH
O
Pi
C
CH2
C
O-
O
C
Pi
C
O-
O
CH2
+
CH2
Pi
C
O-
O
NH
+ Pi
Roundup (Glyphosate) is a very strong inhibitor of EPSP1 Synthase.
Glyphosate
Shikimate3-phosphate
EPSPPEP
1EPSP = 5-ENOLPYRUVYLSHIKIMATE 3-PHOSPHATE
Phe, Trp, Tyr
Sulfonylurea Tolerant Soybeans - STS -These cultivars are resistant to certain sulfonyl ureas (SUs), a family of herbicides which are most effective against broadleaf weeds. STS herbicides used over soybean varieties that have the STS gene offer the benefit of using broad spectrum sulfonylurea broadleaf herbicides without injuring young soybean plants.
Labeled sulfonylurea herbicides include Synchrony STS¹, Reliance STS¹, Classic¹, Pinnacle¹, Canopy¹, Canopy XL¹ and Concert¹.
The STS gene was incorporated into soybean germplasm using conventional breeding methods.
SU tolerant gene induced by EMS mutagenesis (US patent # 5,084,082).
Bx breeding
SUs inhibit the essential plant enzyme acetolactatesynthase or ALS. Animals do not have ALS.
Mechanism of action of SUs
-keto butyrate
pyruvate
acetolactate
ALS
isoleucine
CO2
HC
HC
CH2
CH3
O-
O
O HC
C
CH
CH3
O-
O
OH
HC
HC
CH3
O-
O
O
O
H2CH3C
HC
HC
CH
CH2
O-
O
NH2
CH3
H3C
+
+
Charles Darwin...“It is not the
strongest species that survive, nor the most intelligent, but the ones most responsive to change”
“I’m all for progress; it’s change I don’t like” - Mark Twain
Slide from C.S. Prakash
