modern approaches to crop improvement nir ohad tau
TRANSCRIPT
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Modern Approaches to Crop Improvement
Nir Ohad TAU
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Mechanisms of Asexual Reproduction
a)Fragmentation, separation of a parent plant into
parts that develop into whole plants, is a very
common type of asexual reproduction
b)In some species, a parent plant’s root system
gives rise to adventitious shoots that become
separate shoot systems
strawberries produce runners
which take root and form new strawberry plants
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Nir Ohad, Department of Plant
Sciences, Tel Aviv University
Plant reproduction through
Double Fertilization
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Root apical
meristems
Lateral
meristems
Vascular
cambium
Cork
cambium Axillary bud
meristem
Shoot tip
(shoot apical
meristem and
young leaves)
Plants maintain ability to grow from shoot and
root throughout their life
Embryo
Endosperm
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Ohad N., Dep. of Plant Sciences, TAU
כול הזכויות שמורות
Ave rage precen composition
Protein Oil Carbohydra te Major Storage organ
Cereals
Maize 10 5 80 Endosperm
Wheat 12 2 75 Endosperm
Legumes
Garden pea 25 6 52 Cotyledons
Soybean 37 22 12 Cotyledons
Other
Caster bean 18 64 / Endosperm
Storage reserves of Some important crop species
Most of our Nutrition Derives from Cereals
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Modifying crops by breeding & genetic engineering
a) People have intervened in the reproduction and
genetic makeup of plants for thousands of years
b) Hybridization is common in nature and has been used
by breeders to introduce new genes
c) Maize, a product of artificial selection, is a staple in
many developing countries
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Plant Breeding
a) Mutations can arise spontaneously or
can be induced by breeders
b) Plants with beneficial mutations are
used in breeding experiments
c) Desirable traits can be introduced from
different species or genera
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The hard casings around many grains were eliminated
Photo by Hugh Iltis; Reprinted from Doebley, J.F., Gaut, B.S., and Smith, B.D. (2006). The Molecular
Genetics of Crop Domestication. Cell 127: 1309-1321, with permission from Elsevier.
Teosinte, the wild
relative of maize,
has hard
coverings over
each grain.
Humans selected
against these
during maize
domestication.
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Decrease in branching and increase in seed size were also selected for
Image credit Nicolle Rager Fuller,
National Science Foundation
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Domestication through genome modification gave us modern crops
From Dubcovsky, J. and Dvorak, J. (2007). Genome Plasticity a Key Factor in the Success of Polyploid Wheat Under Domestication. Science.
316: 1862-1866. Reprinted with permission from AAAS.
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Breading Wheat
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Tomato Breading
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Example: Introgression of a disease resistance gene
We cross the two plants.
Some of their progeny
inherit the disease
resistance trait, some don’t
– how can we tell the
difference?
Photo by Stephen Ausmus USDA
We want to add a
disease resistance
trait to an “elite”
tomato plant.
Poor tomato but disease resistant (resistance gene indicated)
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Example: Introgression of a disease resistance gene
After several
generations, elite,
disease resistant
tomato
Markers greatly
accelerate breeding
programs
Implication- Time
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Genetic Modification (GM) is another breeding method
Elite tomato Poor tomato but disease
resistant
Elite, disease resistant tomato
Recombinant DNA (or
GM) allows a single
gene to be introduced
into a genome. This
method can be faster
than conventional
breeding
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Plant Biotechnology and Genetic Engineering
a) Plant biotechnology has two meanings
a)In a general sense, it refers to innovations in the use of
plants to make useful products
b)In a specific sense, it refers to use of GM organisms in
agriculture and industry
b)Transgenic organisms are those that have been
engineered to express a gene from another species
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איך יוצרים צמח טרנסגני
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Agrobacterium tumefaciens are bacteria that live in the soil and transform plants
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Crown gall disease
Edward L. Barnard, Florida Department of Agriculture and Consumer Services, Bugwood.org; Mike Ellis, Ohio State University; University
of Georgia Plant Pathology Archive, University of Georgia, Bugwood.org; Wikimedia commons
The first written record of
crown gall disease, on
grape, dates from 1853
Fridiano Cavara
(1897) found that a
bacterium causes
crown gall in grape
Crown gall induces growths at
wound sites and severely limits
crop yields and growth vigor
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The major steps in plants transformation by
Agrobacterium 1. Recognition
2. Infection
3. Transformation
4. Taking over /inducing Galls
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Ti plasmid Chromosome
T-DNA
Agrobacterium
tumefaciens Transformed
Plant Cell
How do Agrobactrium transform plant cells?
Tumor synthesizes opines On which bacterium can grow
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The Ti plasmid can be used to introduce any gene into plants
Hoekema, A., Hirsch, P.R., Hooykaas, P.J.J. and Schilperoort, R.A. (1983). A binary plant vector strategy based
.180-179: 303plasmid. Nature. -Ti Agrobacterium tumefaciensregion of the -and T -on separation of vir
The discovery that T-DNA was inserted into
the plant genome raised the possibility that
“any gene” could be transferred into plants T-DNA
pTi
Tumor-inducing and opine
synthesis genes on T-DNA can be
” gene of interestby a “ replaced
selectable marker and
Gene of interest Selectable
marker
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GM Example: Insect resistance through introduction of the Bt gene
Wild-type peanut plant Peanut plant expressing the Bt gene
Photo by Herb Pilcher USDA
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The effect of Bt toxin is highly specific
Bacillus
thuringiensis
expressing Bt
toxin
Plant cell
expressing Bt
toxin
Pore
assembly
Intestine
After binding, the insecticidal
proteins assemble to form a pore in
the lining of the insect intestine
which kills the insect
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Reducing World Hunger and Malnutrition
a)Genetically modified plants may increase the
quality and quantity of food worldwide
b)Some transgenic crops have been developed to
produce the Bt toxin, which is toxic to insect
pests
c) Other crops are able to tolerate herbicides or
resist specific diseases
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Photo credit: Doug Buhler, Bugwood.org
Plants compete
with other plants for
sunlight and
nutrients. Many
farmers use
herbicides to
eliminate weeds
(undesired plants)
from their fields.
Left – corn rows sprayed with herbicide to eliminate competing plants
Right – corn being choked by giant foxtail (Setaria faberi) זיפן ירוק
GM Example: Herbicide resistance
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Herbicide tolerant plants are environmentally friendly
Cerdeira, A.L. and Duke, S.O. (2006). The Current Status and Environmental Impacts of Glyphosate-Resistant Crops. J.
Environ. Qual. 35: 1633-1658. Photo credit Hunt Sanders, University of Georgia, bugwood.org.
Farmers that plant herbicide-
tolerant crop plants use less
herbicide, herbicides that are less
toxic, and till (plow) less, saving
soil and fuel.
Soybean
*
*
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GM Use includes among other:
• Biofortification as a Weapon Against Malnutrition
• “Golden Crops” (pro-Vit A)
• Hi Iron/zinc Crops
• Biotic and Abiotic Stress resistance.
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Vitamin A
Essential for the immune system
Deficiency affects more than 100m children and is responsible
for up to one quarter of child deaths in affected areas
Providing Vitamin A can increase survival rates by about 23%
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Sources of Vitamin A
Humans cannot make Vitamin A (retinol)
but can get it from eating meat, fish, dairy
A second source comes from eating
plants rich in carotenoids—often called
Pro-Vit A
Humans can convert carotenoids to Vit A
Carotenoids are colored pigments that
can absorb light. Accessory pigments in
photosynthesis. They are also powerful
anti-oxidants
Most commonly associated with orange-
fleshed vegetables such as carrots and
sweetpotatoes
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Engineering Golden Rice
Only 2 genes are lacking in rice endosperm to make B-carotene (Pro VitA) In first version of Golden Rice (GR1), phytoene synthase came from daffodil; In current version (GR2), it comes from maize In both GR1 and GR2, crt1 gene (encodes a desaturase), comes from the bacterium Erwinia Both are expressed on an endosperm-specific promoter so only expressed in endosperm of rice.
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The Outcome
GR1 1.6 ug/ GR2 37 ug/g
The team:
Ingo Potrykus, ETH, Zurich
Peter Beyer, University Frieburg)
Adrian Dubock, Syngenta
A new variety of golden rice
with that contains 23X more b-
carotene compared to golden
rice-1.
Golden rice has been
introduced into common rice
varieties
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Good News, Bad News
• As a result of intense global
opposition, work has been
set back many years
• Some serious development
mistakes at IRRI o Backcrossing into local lines before
they were sure they had a good
event
o Put all their eggs in too few events;
now it turns out these events show a
yield penalty in field trial—something
not seen in greenhouse
• Engineering expression took a
long time but is a great technical
success
• Intellectual property agreement
between scientists and Syngenta
finally agreed upon
• After many years of subsequent
development at IRRI, golden rice
has finally been allowed into field
trials in Philippines and
Bangladesh
• Human feeding trials indicate
that the B-carotein is absorbed at
high efficiency in humans
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The Debate over Plant Biotechnology
Some people are concerned about risks of releasing
GM organisms (GMOs) into the environment
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Possible Effects on Nontarget Organisms
a)Many ecologists are concerned that the growing
of GM crops might have unforeseen effects on
nontarget organisms
PNAS , 2015
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CRISPR Cas9 Genome Editing
Plants
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CRISPR Cas9 Genome Editing
a) The CRISPR/Cas system is a prokaryotic immune
system that confers resistance to foreign genetic
elements such as those present within plasmids and
phages that provides a form of acquired immunity
b) A simple version of the CRISPR/Cas system,
CRISPR/Cas9, has been modified to edit genomes.
By delivering the Cas9 nuclease complexed with a
synthetic guide RNA (gRNA) into a cell, the
cell's genoe can be cut at a desired location, allowing
existing genes to be removed and/or new ones added
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The Challenge for regulators is to identify a single nucleotide change