Transgenic Plants Flashcards
What are transgenic plants ?
These contain genes/gene which have been changed or inserted artificially
What are transgenic plants often called?
GM foods
What event revealed evidence of horizontal gene transfer?
A genome-wide analysis of millet and rice revealed the first clear evidence of horizontal gene transfer in plants (Monroe, 2005)
Why make transgenic plants?
To improve the growth characteristics & yield of agriculturally valuable crops
- To increase the nutritional value of crops
- To provide crops with resistance against:
- insects
- viral pests
- drought
- herbicides
What are the 3 steps in making transgenic plants?
Gene manipulation
Identify and isolate a gene that controls a trait of interest from another species
-Or create a new allele by modifying an existing gene
Gene introduction
- introduce new gene into plants
- direct DNA transfer (electroporation, micro injection, gene-gun)
- Agrobacterium mediated gene-transfer
Selection and regeneration
- Plant is transformed (identified by a selectable marker) - Transformed cell regenerates and transgenic plant is formed
What are the methods used in plant transgenesis?
- protoplast fusion
- Leaf fragment technique
- Particle Bombardment technique
- Chloroplast engineering
- Antisense technology
Describe protoplast fusion
- injured cells produce a mass of cells called callus over the site of wound
- Callus cells are capable of forming shoot, roots or a whole organism
- Callus can be made to contain new genes (reprogrammed)
- Digest cellulose of callus or plant cells
- fuse protoplast to protoplast from a different species
E.g. used to create broccoflower from broccoli and caulk form
Physical attributes of cauliflower, but has the color of the broccoli
Describe leaf fragment technique
Cut small discs from leaf and use genetically modified Agrobacter
Limitation is that Agrobacter can only infect dicotyledonous plants like:
-tomatoes
- potatoes
- apples
- soybeans
Describe Particle Bombardment using Gene-gun
Shoot (blast) tiny metal beads coated with DNA into:
- nucleus of:
- embryonic cells
- intact leaves
- soft kernels
- Chloroplast
Blast velocity
-about 430 meters/second
A marker, e.g. antibiotics is used to select only genetically transformed cells
Describe chloroplast engineering
Chloroplast DNA can accept several mew genes at once, unlike DNA in a cell’s nucleus
- A high percentage of genes inserted into the chloroplast will remain active when the plant matures
- DNA in chloroplast in separate from the DNA released in plant’s pollen
Describe Old Method of Cloning Multiple Genes
Two plants are produced, each on its own inserted gene
- crossing by pollen transfer used to produce hybrid plant
- Pollen can be transferred to other non-target plants and possibly beneficial insects
- cauliflower mosaic virus (CaMV)
Explain Agrobacterium mediated gene-transfer
Genetic transfers occurs naturally in plants
- When their wounds are infected by Agrobacterium tumefaciens(Agrobacter)
- This soil bacteria contains a large double-stranded DNA molecule called a plasmid
- This plasmid is also refferred to as tumor-inducing (TI) plasmid,
- because it triggers an uncontrolled growth of the cells (tumor) in the plant
Explain using intermediate vectors to produce a transgenic plant with TI plasmids
An intermediate vector of manageable size is used to clone the segment of interest (gene)
- the intermediate vector is then recombined with an attenuated (“disarmed”) Ti plasmid to generate a cointegrate structure bearing the insert of interest and
- A selectable plant marker (kanamycin-resistance) between the T-DNA borders
Explain antisense technology
Polyglacturonase(PG)- an enzyme that digests pectin on the wall of the plant to induce normal decay
Agrobacter vector used to transfer the new gene that encodes the antisense mRNA molecule that unites with and inactivates the normal sense mRNA molecule for PG production
Antisense Technology also exploited for bruise resistant potatoe, and splicing genes for increased protein content from chicken into potatoes
What are reporter genes?
Used to monitor the function of any gene during development
What are the examples of reporter genes?
- luciferase gene
- bacterial GUS (b-glucuronidase) gene
- bacterial lac(b-galactosidase) gene
- jellyfish green fluorescent gene
What are the luciferase gene?
A reporter gene(which is isolated from fireflies) which produces luciferase. Luciferase catalyzes the reaction of a chemical called Luciferin with ATP, in this process, light is emitted, which explains why fireflies glow in the dark. A transgenic tobacco plant expressing the luciferase gene also will glow in the dark when watered with a solution of luciferin
What are the bacterial GUS (b-glucuronidase) gene?
Turns the compound to X-Gluc blue
What are the bacterial lac(b-galactosidase) gene?
Turns X-gal blue
What are jellyfish green fluorescent gene?
Which causes cells that express the GFP to glow green under blue light
What are the advantages of plant transgenesis ?
- Wealth of information on strains that can be exploited at the molecular level because plant breeding has a long history
- Plants produce a large number of progeny. Therefore, rare mutations and recombinations can be discovered with more ease .
- Plants’ regenerative capabilities is better than that of animals.
- Many plants can regenerate from a single cell to form a genetic replica(clone) of the parent cell
-With plants, species boundaries and sexually compatibility are not issues
What are the problems of plant molecular biology?
Molecular analysis of plants cells has lagged behind that of animal cells because:
- Research priorities and allocation of federal funds to plant molecular biology aren’t high
- Plants grow slowly and have relatively long generation times
- Plants have large genomes. For instance, the haploid corn genome (15 billion base pairs) is about 5 times larger than the human genome
- Plant cells are surrounded by a wooden box (cellulose cell wall), making them resistant to the introduction of foreign DNA)
What are the current and possible benefits of GM/Transgenic plants?
- increased productivity
- Contribution to global food security/ elimination of hunger
- Higher quality crops
- tastier and healthier fruits
- More valuable economics crops
Contrast traditional and Flavr Savr
The Flavr Savr tomato ripens on the vine- resulting in the fuller flavor. It is modified so that it remains firm after harvesting
Ripe and increased flavor
The traditional tomato must be harvested while it is still green and firm so that it is not crushed on the way to the supermarket
Sprayed with ethylene after shipping to induce ripening
Ripe but decreased flavor
