Plant Biotechnology Chapter 6. Motivation for genetically engineered crops Agriculture is the biggest industrial sector in the world –$1.3 trillion of.

Plant Biotechnology

Chapter 6

Motivation for genetically engineered crops

• Agriculture is the biggest industrial sector in the world– $1.3 trillion of products/year

• Over past 40 years, world population has doubled while agricultural land area has increased by only 10%

Plant transgenics

• Transfer of genes to plants directly accelerates selective breeding practices used in the past.– Cotton fiber strength

• increased 1.5% per year through conventional breeding

• Increased 60% by inserting a single gene into the plant

– Corn and soybean have been targets of much genetic engineering

• Cloning– Many types of plants can regenerate from a

single cell, similar to a bacterium.– The resulting plant is a clone or replica of

plant from which original cell was taken.

• Protoplast fusion– Introducing a gene into a “denuded” plant cell

and generating a new plant

Genetic engineering techniques applied to plants

Protoplast fusion

Callus cells

Plant A Plant B Hybrid plantLeaf fragment technique

Agrobacterium tumefaciens as a vector for transferring foreign genes into plant

chromosome• This bacterium naturally infects plant cells

causing cancerous growths - crown gall disease

• Infection (vir) genes carried on Ti plasmid

Infection Process

• Vir genes copy T-DNA• Open channel in bacterial

cell membrane for T-DNA to pass through

• T-DNA enters plant through wound, integrates itself into plant chromosome

http://www.bio.davidson.edu/people/kabernd/seminar/2002/method/dsmeth/ds.htm

Leaf fragment technique used to introduce foreign genes into plant

• Small discs are cut from plant leaf• Discs are cultured to start a new plant• Early in the regeneration process, the bacterium

Agrobacterium tumefaciens carrying a Ti plasmid is introduced into the culture

• The plasmid DNA combines with the plant chromosome

• Discs are treated with hormones to encourage shoot and root development and then the new plant is planted in the soil

Make leaf discs

Briefly culturediscs withgeneticallymodified Agrobacterium

Transfer to filterpaper over nursecells

Culture 2-3 days

Transfer to shoot stimulating medium

Leaf fragment technique

Agrobacteriumwith Ti plasmidwith foreign gene

Gene guns

Gene gun

stopped

Antisense technology• Used to produce the Flavr-Savr tomato in 1994.• Enzyme polygalacturonase breaks down

structural polysaccharide pectin in wall of a plant.

• This is part of the natural decay process in a plant

• Monsanto identified the gene than encodes the enzyme and made another gene that blocked the production of the enzyme.

Antisense molecules

Natural insecticide produced by soil bacterium

• The bacterium Bacillus thuringiensis produces a crystalline protein that if ingested by insects acts as a toxin and kills the insect

• Farmers used to spray their fields with spores of the bacteria to inoculate the plant leaf surface before it is attacked by the insect

Insecticide biotechnology

• The gene coding for the crystalline protein (Cry) was transferred from the bacterium to the plant.– How can they do this?

• Now the plant produces the toxin protein, so don’t need to inoculate with bacterium– This strategy kills the pest before

it kills the plant

Plant vaccines• Plants are susceptible to diseases caused by

viruses (tobacco mosaic virus)• Virus surface protein induces an immune

response in the plant against the virus protein• Researchers inserted the virus protein into the

plant genome using the Ti plasmid/ Agrobacter vector

• Now the plant produces a small quantity of the protein which elicits an immune response by the plant the way a vaccine does

Concerns about genetically modified foods

• Human health– Unsuspected allergens– What other issues are there?

• Environment

• Messing up the gene pool of non-target species in the environment– Lateral gene transfer in nature

• Still poorly understood in nature

National biofuels initiative• In 2007, the federal government increased

funding for research in biofuels (ethanol and biodiesel)

• Idea was to– produce ethanol from corn– convert agricultural waste products (lignocellulose) to

ethanol

• This requires re-engineering natural biochemical pathways in plants or microbes to produce more fuel as an end-product

How is ethanol produced?

• Most ethanol is produced using a four-step process: – The ethanol feedstock (crops or plants) are

ground up for easier processing – Sugar is dissolved from the ground material, or

the starch or cellulose is converted into sugar – Microbes feed on the sugar, producing ethanol

and carbon dioxide as byproducts – The ethanol is purified to achieve the correct

concentration.

Metabolic engineering to improve efficiency of biological production of biofuels

Natural metabolic pathway

1 ton of Feedstock X product A product D product E 150 gal Ethanol

Genetically engineered metabolic pathway

1 ton of Feedstock X product A product B product C 50 gal Ethanol

product G 50 gal Butanol New enzyme

Benefits of ethanol

• Overall, ethanol is considered to be better for the environment than gasoline. – Ethanol-fueled vehicles produce lower carbon

monoxide and carbon dioxide emissions, and the same or lower levels of hydrocarbon and oxides of nitrogen emissions.

• Ethanol is widely available and easy to use

• Ethanol is good for the economy

Drawbacks of ethanol as a biofuel

• Creating plant-based biofuels requires too much farmland to be practical or sustainable—land that would be better used to grow food.

• Producing ethanol and other biofuels takes more energy than the fuel can generate.

Summary

• Variety of techniques are available to introduce genes into plants and have the plants express the gene

• Such genetic engineering is used to– Improve disease resistance– Flavor of product– Nutrition of product– Shelf life of product– Any other property of plant that improves its

value

• Advances in biotechnology of biofuel production will be the next greatest application of our knowledge of biology to address challenges to our society and high-maintenance lifestyles.