Chapter 6

1. Chapter 6 Plant Biotechnology and Food

2. Chapter Contents • 6.1 Agriculture: The Next Revolution • 6.2 Methods Used in Plant Transgenesis • 6.3 Practical Applications in the Field • 6.4 Health and Environmental Concerns

3. 6.1 Agriculture: The Next Revolution • Plant Transgenesis – transferring genes to plants directly • Development of plant vaccines, plants that produce their own pesticides and are resistant to herbicides • 17 countries are growing more than 200 million acres of crops improved through biotechnology • Focus of considerable controversy

4. 6.2 Methods Used in Plant Transgenesis • Conventional Selective Breeding and Hybridization • Cloning • Protoplast fusion • Leaf fragment technique • Gene guns • Chloroplast engineering • Antisense technology

5. 6.2 Methods Used in Plant Transgenesis • Conventional Selective Breeding and Hybridization • Sexual cross between two lines and repeated backcrossing between hybrid offspring and parent • Can take years • Polyploid plants (multiple chromosome sets greater than normal) • Increases desirable traits, especially size • Whole chromosomes can be transferred rather than single genes

6. 6.2 Methods Used in Plant Transgenesis • Cloning – growing plants from a single cell • Protoplast fusion is the fusion of two protoplast cells from different species • Protoplast cell is a callus cell whose cell wall has been dissolved by the enzyme cellulase • Fusion of the two protoplast cells creates a cell that can grow into a hybrid plant • Examples include broccoflower

7. 6.2 Methods Used in Plant Transgenesis

8. 6.2 Methods Used in Plant Transgenesis • Cloning • Leaf fragment technique • Small discs are cut from leaf • Cultured in a medium containing genetically modified Agrobacter (Agrobacterium tumefaciens) • A soil bacterium that infects plants • Bacterium contains a plasmid, the TI plasmid, that can be genetically modified • DNA from the TI plasmid integrates with DNA of the host cell • Leaf discs are treated with plant hormones to stimulate shoot and root development

9. Process of crown gall formation in plants

10. A detail photo of a crown gall on a Kalanchoë infected with Agrobacterium tumefaciens http://en.wikipedia.org/wiki/File:Crown-gall_detail.jpg

11. 6.2 Methods Used in Plant Transgenesis Leaf fragment technique • Transfer of genetically modified Ti plasmid to susceptible plants through tissue culture • Agrobacter cannot infect monocotyledonous plants (single seed embryo) such as corn and wheat

12. 6.2 Methods Used in Plant Transgenesis • Cloning —Gene Guns • Used to blast tiny metal beads coated with DNA into an embryonic plant cell • Aimed at the nucleus or the chloroplast • Use marker genes to distinguish genetically transformed cells • Antibiotic resistance • Technique is useful in plants that are resistant to Agrobacter (monocotyledonous plants)

13. Gene Gun • Velocities about 430 m/s • Targets can include suspensions of embryonic cells, intact leaves, and soft seed kernels.

14. 6.2 Methods Used in Plant Transgenesis Cloning • Chloroplast engineering • DNA in chloroplast can accept several new genes at once • High percentage of genes will remain active • DNA in chloroplast is completely separate from DNA released in pollen – no chance that transformed genes will be carried on wind to distant crops Insect-resistant genes: Orf1, Orf2, Cry2Aa2 Inserted into 16S ribosome gene of chloroplast Trn1 and TrnA: flanking regions of the 16S site aadA: selection site for antibiotic resistance Prrn: primer binding site for PCR psbA3: stabilize foreign genes

15. 6.2 Methods Used in Plant Transgenesis • Cloning • Antisense technology • Process of inserting a complementary copy of a gene into a cell • Gene encodes an mRNA molecule called an antisense molecule • Antisense molecule binds to normal mRNA (sense molecule) and inactivates it • Example is Flavr Savr tomato Ripe tomato secretes Polygalacturonase (PG) which digests pectin in the wall of the plant

16. 6.3 Practical Applications in the Field • Vaccines for plants • Genetic pesticides • Safe storage • Herbicide resistance • Stronger fibers • Enhanced nutrition • The future: from pharmaceuticals to fuel • Metabolic engineering

17. 6.3 Practical Applications in the Field • Vaccines for Plants • Vaccine is encoded in a plant’s DNA • For example, a gene from Tobacco Mosaic Virus (TMV) inserted into tobacco plants • Protein produced from the viral gene stimulates the plant’s immune system • Plant is invulnerable to virus

18. 6.3 Practical Applications in the Field • Genetic Pesticides • Bacillus thuringiensis (Bt) is a bacterium that produces a protein that kills harmful insects and their larvae • Crystalline protein from Cry gene fuses the lining cells of the digestive tract of certain insects– insects die due to “autodigestion”. • Bt genes can be inserted into a plant’s DNA • Creates a built-in defense against certain insects • Controversy surrounding Monarch butterflies http://www.learner.org/courses/biology/archive/images/1006.html http://www.extension.iastate.edu/newsrel/2003/jul03/jul0328.html

19. 6.3 Practical Applications in the Field • Safe Storage • Millions of dollars are lost every year to insect infestations of crops during storage • Transgenic corn that expresses avidin is highly resistant to pests during storage • Avidin blocks the availability of biotin, a vitamin required by insects to grow • Herbicide Resistance • Genetically engineer crops to be resistant to common herbicides • Allows farmers to control weeds with chemicals that are milder and more environmentally friendly than typical herbicides • Common herbicide: glyphosphate, block an enzyme for photosynthesis. Soybeans resistant to glyphosphate are the successful example

20. 6.3 Practical Applications in the Field

21. 6.3 Practical Applications in the Field • Stronger Fibers • Biotechnology increased the strength of one variety of cotton by 60%, while classical breeding can only increase 1.5% • Softer, more durable clothes for consumers • Greater profits for farmers • Enhanced Nutrition • Golden rice has been engineered to contain large amounts of beta carotene, which the body converts to vitamin A • The Future: From Pharmaceuticals to Fuel • Plants can be ideal protein factories • Used to grow medicines • Vaccines for humans, antibodies, human insulin • Plant-based petroleum for fuel, alternatives to rubber, nicotine-free tobacco, caffeine-free coffee, biodegradable plastics, stress-tolerant plants

22. 6.3 Practical Applications in the Field

24. 6.3 Practical Applications in the Field • Metabolic Engineering • Manipulation of plant biochemistry to produce non-protein products or to alter cellular properties • Alkaloids: quinine (drug), lipids: (long chain unsaturated fatty acids to lower cholesterol in food), polyterpenes: new kinds of rubber, pigment production: blue delphinidin in flower, and biodegradable plastics: polyhydroxyanakanoates • Involves transfer of more than one gene and more finite regulation

25. 6.4 Health and Environmental Concerns

26. 6.4 Health and Environmental Concerns • Human Health • Opponents fear the effects of foreign genes, bits of DNA not naturally found in plants • Allergic reactions • Antibiotic-resistance marker genes could spread to disease-causing bacteria in humans • Cause cancer • To date, science has not supported any of these concerns

27. 6.4 Health and Environmental Concerns • Environmental Concerns • Genes for pest or herbicide resistance could spread to weeds • Few experts predict this will happen; further studies are needed • Regulation • FDA regulates foods on the market • USDA oversees growing practices • EPA controls use of Bt proteins and other pesticides