Plant Biotechnology

Chapter 6Fall 2008

CO2 + H2O →C6H12O6 + O2

Agriculture: The Next Revolution Biggest industry in the world ($1.3 trillion of

products per year) Plant transgenesis allows innovations that are

impossible to achieve with conventional hybridization methods (e.g. conventional -> strength of cotton 1.5%; insertion of a single gene > strength 60%!) Resistant to herbicides Pest resistant Vaccines

74% of all soybean crops are genetically modified

32% of all corn

Methods Used in Plant Transgenesis

Unique advantages of plants: The long history of plant breeding provides

plant geneticists with a wealth of strains that can be exploited at the molecular level

Plants produce large no.s of progeny; so rare mutations and recombinations can be found more easily

Plants have been regenerative capabilities, even from one cell

Species boundaries and sexual compatibility are no longer an issue

Protoplast Fusion (figure 6.2)

When injured, a mass of cells called a callus may grow over the site

Callus cells have the capability to redifferentiate into shoots and roots

Must remove the cellulose around these cells before DNA can be introduced; produce a protoplast

Leaf Fragment Technique (figures 6.3 & 6.4)

Small discs of leaf incubated with genetically modified Agrobacter Ti plasmid

Treat with hormones to stimulate shoot and root development

Limitation: cannot infect monocotyledonous plants only dicotyledonous such as tomatoes, potatoes, apples and soybeans

Gene Guns

Use on Agrobacter-resistant crops Blast tiny metal beads coated with DNA

into an embryonic plant cell (figure 6.5) Aim at the nucleus or a chloroplast Shoot in gene of interest and a gene marker

(reporter) Why is it more advantageous to genetically

alter chloroplasts vs the nucleus? More genes can be inserted at one time, more

likely to be expressed, DNA is separate from the nucleus (figure 6.6)

Antisense Technology

Flavr SavrTM tomato introduced in 1994 Ripe tomatoes normally produce the

enzyme, polyglacturonase (PG) which digests pectin

Scientists isolated gene, produced a complementary gene which produces a complementary mRNA that binds to the normal mRNA inactivating the normal mRNA for this enzyme (figure 6.7)

RNA interference

Inhibits gene expression by interfering with transcription or translation of RNA molecules

http://www.pbs.org/wgbh/nova/sciencenow/3210/02.html

Practical Applications in the Field (table 6.1)

Vaccines for Plants (figure 6.8) Genetic Pesticides

Bacillus thuringiensis (Bt) Safe Storage (avidin-blocks the

availability of biotin for insects) Herbicide Resistance –resistant to

glyphosate (figure 6.10) Stronger fibers (already mentioned) Enhanced Nutrition Golden Rice (vit A)

The Future: From Pharmaceuticals to Fuel

Plant-based petroleum for fuels, alternatives to rubber, nicotine-free tobacco, etc

Metabolic Engineering

Manipulation of plant biochemistry to produce nonprotein products or to alter cellular properties

Health and Environmental Concerns

Human Health Allergens

Environment Super weeds