Modern Approaches to Crop Improvement Nir Ohad TAU

© 2015 Pearson Education Ltd

Modern Approaches to Crop Improvement

Nir Ohad TAU


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

Nir Ohad, Department of Plant

Sciences, Tel Aviv University

Plant reproduction through

Double Fertilization


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

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


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


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


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.

http://teosinte.wisc.edu/images.html

http://dx.doi.org/doi:10.1016/j.cell.2006.12.006




Decrease in branching and increase in seed size were also selected for

Image credit Nicolle Rager Fuller,

National Science Foundation

http://www.nsf.gov/news/news_images.jsp?cntn_id=114445&org=NSF


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.

http://www.sciencemag.org/content/316/5833/1862.abstract




Breading Wheat


Tomato Breading


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)

http://www.ars.usda.gov/is/graphics/photos/jul03/k10498-2.htm


Example: Introgression of a disease resistance gene

After several

generations, elite,

disease resistant

tomato

Markers greatly

accelerate breeding

programs

Implication- Time


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


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


איך יוצרים צמח טרנסגני


Agrobacterium tumefaciens are bacteria that live in the soil and transform plants


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

http://www.forestryimages.org/browse/detail.cfm?imgnum=4823037

http://plantpath.osu.edu/people-and-programs/faculty-directory/ellis-michael-a/

http://fruit.cfans.umn.edu/grape/pictures/crowngall.jpg



http://ru.wikipedia.org/wiki/%D0%A4%D0%B0%D0%B9%D0%BB:Acta_Horti_berg._-_1905_-_tafl._135._-_Fridiano_Cavara.jpg


The major steps in plants transformation by

Agrobacterium 1. Recognition

2. Infection

3. Transformation

4. Taking over /inducing Galls


Ti plasmid Chromosome

T-DNA

Agrobacterium

tumefaciens Transformed

Plant Cell

How do Agrobactrium transform plant cells?

Tumor synthesizes opines On which bacterium can grow


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

http://www.nature.com/nature/journal/v303/n5913/abs/303179a0.html




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

http://ars.usda.gov/is/ar/archive/nov99/pest1199.htm


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


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


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



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

*

*

https://www.agronomy.org/publications/jeq/articles/35/5/1633





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.


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%

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

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.

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

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


The Debate over Plant Biotechnology

Some people are concerned about risks of releasing

GM organisms (GMOs) into the environment


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


CRISPR Cas9 Genome Editing

Plants


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


The Challenge for regulators is to identify a single nucleotide change

Modern Approaches to Crop Improvement Nir Ohad TAU

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