Objectives of applied plant physiology:
Increase productivity via:
– Enhanced efficiency or resistance
– Reduce losses to pests, stress, weeds
How do we increase yield despite marginal environments?
– Traditional breeding; artificial selection
• Hybrids (2 species or cultivars crossed; generally close relatives)
• Induce mutations  tissue culture mutations
• Find unique genotypes; propagate; use DNA markers that are tightly-linked
to target loci (marker assisted selection)
Time intensive, but effective
CONVENTIONAL PLANT BREEDING
P1
x
P2
Donor
Recipient
F1
F2
large populations consisting of
thousands of plants
PHENOTYPIC SELECTION
Salinity screening in phytotron
Glasshouse trials
Bacterial blight screening
Phosphorus deficiency plot
Field trials
MARKER-ASSISTED BREEDING
Susceptible
P1
x
P2
Resistant
F1
F2
large populations consisting of
thousands of plants
MARKER-ASSISTED SELECTION (MAS)
Advantages - Selection at seedling stage, no environmental effects and can discriminate
between homozygotes and heterozygotes
Disadvantages – cost, technical expertise, marker must be tightly linked to trait of interest
(<5cM of marker)
Objectives of applied plant physiology:
Increase productivity via:
– Enhanced efficiency or resistance
– Reduce losses to pests, stress, weeds
How do we increase yield despite marginal environments?
– Traditional breeding; artificial selection
• Hybrids (2 species or cultivars crossed; generally close relatives)
• Induce mutations  tissue culture mutations
• Find unique genotypes; propagate; use DNA markers that are tightly-linked
to target loci (marker assisted selection)
Time intensive, but effective
– GMOs; transgenic plants
• Recombinant DNA technology
• Tissue culture of transformed cells
– Time and $$ intensive
– Concerns by public (explore on T)
What traits could we modify?
What traits are we modifying?
Herbicide resistance (so we can spray fields with herbicide and not kill the crop)
Insect resistance (so we don’t spray pesticides, the plants make the toxins)
Disease resistance
Enhanced shelf life, oil or nutritional content (golden rice)
– All of these are generally single gene traits
Hyperaccumulators – clean pollution
Stress tolerance to drought, heat, cold, salt, pollution
N fixation, C4 PSN
– Problem with these = multiple genes or they involve symbiotic interactions,
which are harder to transform
Agrobacterium tumifaciens
Crown gall disease – a bacterium
–
–
–
–
Widespread
enters plant via wounds
causes cancer-like tumors (crown gall disease)
can reduce productivity
– Gall grows and divides (even if bacteria
dies)
• Gall tissues have high [CK] and [IAA]
• Opines (unusual a.a.) made (C source)
– Agrobacterium transfers its plasmid into
plant’s DNA
• Interkingdom horizontal DNA/gene transfer!
Lateral gene transfer by A. tumifaciens
Tumor inducing = (Ti) plasmid:
– Vir genes activated in response to plant wound signals
– T-DNA (endonuclease) cuts host DNA and then inserts its genes into host DNA!
– Bacterial DNA w/ eukaryotic gene promoters code for:
• IAA, CK synthesis; causes cell proliferation = home for bacterium
• Modified amino acids; unique C and N source for bacterium
Is this useful?
We can make transgenic plants:
Remove aa and hormone synthesis genes; Keep endonuclease
Gene added from another species; new trait (e.g. herbicide, pest resistance)
Selectable marker added (usually antibiotic resistance gene or GFP)
Plant cells (tissue discs) exposed to transformed Ti plasmid
New gene(s) integrated into plant DNA
– Transformed individuals selected on antibiotic plates
Whole plants regenerated w/ tissue culture
A. tumifaciens transformation:
Only works well on dicots
Most of the world’s crop plants are monocots
How could we transform them?
Some approved commercial releases of transgenic plants
Crop /release date
Name
Company
Novel properties
Tomato (1994)
Flavr Savr
Calgene
Vine-ripened flavor, shelf life
Zeneca
Consistency of tomato paste
Tomato (1995)
Cotton
Potato
Maize (1996-97)
Bollgard
NewLeaf
YieldGuard
Monsanto
Bacillus thuringiensis toxin for insect
feeding resistance
Soybean
Canola (rape)
Cotton (1995-96)
Roundup Ready
Monsanto
Glyphosate herbicide resistance
Simplot
Reduced acrylamide when cooked
Monsanto
Drought resistance
Potato (2014)
Maize (2011)
Papaya, potato,
squash
DroughtGard
Viral resistance
How widespread (acreage) are transgenic crops in the world?
Benefits and costs/objections
Find diversity of opinions that relate to benefits and costs
Find data on:
– Benefits of transgenic crops. Include data.
– Disadvantages/concerns about GM crops. Include data.
– How transgenic organisms are regulated; who?
– Effect on beneficial or non-target insects. Include data.
– Crop to weed gene transfer
– Selecting for resistant insects/pathogens
– Consumer health
– Impact on genetic diversity of crops
– Is there is a reduction in herbicide or pesticide use w/ GMOs?
– What are concerns among people in other nations, esp.
developing nations?
– Colorado State University has a good, but dated website with links.
http://cls.casa.colostate.edu/transgeniccrops/index.html