Presentation on theme: "Plant Genetic Transformation. All stable transformation methods consist of three steps: Delivery of DNA into a single plant cell. Integration of the DNA."— Presentation transcript:
All stable transformation methods consist of three steps: Delivery of DNA into a single plant cell. Integration of the DNA into the plant cell genome. Conversion of the transformed cell into a whole plant.
Only known natural example of DNA transport between Kingdoms 1. (Virulent) strains of A. tumefaciens contain a 200-kb tumor inducing (Ti) plasmid 2. Bacteria transfer a portion of the plasmid DNA into the plant host (T-DNA). T-DNA
Infects at root crown or just below the soil line. Can survive independent of plant host in the soil. Infects plants through breaks or wounds. Common disease of woody shrubs, herbaceous plants, dicots. Galls are spherical wart-like structures similar to tumors.
The T-DNA is transferred from the Bacteria into the Nucleus of the Plant 1. Stably integrates (randomly) into the plant genome. 2. Expression of genes in wild-type T-DNA results in dramatic physiological changes to the plant cell. 3. Synthesis of plant growth hormones (auxins and cytokinins) neoplastic growth (tumor formation)
Genes required to breakdown opines for use as a nutrient source are harbored on the Ti plasmid in addition to vir genes essential for the excision and transport of the T-DNA to the wounded plant cell. T-DNA vir genes opine catabolism pTi ~200 kb tra for transfer to the plant bacterial conjugation 23 kb
vir genes opine catabolism pTi tra for transfer to the plant bacterial conjugation Agrobacterium chromosomal DNA chvA chvB pscA oriV T-DNA- inserts into plant genome
Agrobacterium can be used to transfer DNA into plants
1. Agrobacterium tumefaciens chromosomal genes: chvA, chvB, pscA required for initial binding of the bacterium to the plant cell and code for polysaccharide on bacterial cell surface. 2. Virulence region (vir) carried on pTi, but not in the transferred region (T-DNA). Genes code for proteins that prepare the T-DNA and the bacterium for transfer. Ti plasmids and the bacterial chromosome act in concert to transform the plant
3. T-DNA encodes genes for opine synthesis and for tumor production. 4. occ (opine catabolism) genes carried on the pTi allow the bacterium to utilize opines as nutrient.
Generation of the T-strand overdrive Right Border Left Border T-DNA virD/virC VirD nicks the lower strand (T-strand) at the right border sequence and binds to the 5’ end. 5’
Generation of the T-strand Right border Left border D virD/virC gap filled in T-strand T-DNA virE 1. Helicases unwind the T-strand which is then coated by the virE protein. 2. ~one T-strand produced per cell.
1. Transfer to plant cell. 2. Second strand synthesis 3. Integration into plant chromosome Right border Left border D T-strand coated with virE T-DNA virD nicks at Left Border sequence
pTi-based vectors for plant transformation: 2. Early shuttle vectors integrated into the T- DNA; still produced tumors. 1. Shuttle vector is a small E. coli plasmid using for cloning the foreign gene and transferring to Agrobacterium. E. coli Agrobacterium pTi Shuttle plasmid conjugation
Transformation of Arabidopsis plants Dip floral buds in 1 ml of Agrobacterium culture for 5 to 15 min. Detergent added to allow bacteria to infiltrate the floral meristem.
Transformation of Arabidopsis plants 700 to 900 seeds per plant. Germinate on kanamycin plates to select transformants. 10 to 20 transformed plants per plant. 10 day old seedlings
MiniTi T-DNA based vector for plants 1. Binary vector: the vir genes required for mobilization and transfer to the plant reside on a modified pTi. 2. consists of the right and left border sequences, a selectable marker (kanomycin resistance) and a polylinker for insertion of a foreign gene. Disarmed vectors: do not produce tumors; can be used to regenerate normal plants containing the foreign gene. miniTi
MiniTi T-DNA based vector for plants modified Ti plasmid a binary vector system oriV vir T-DNA deleted 2 LB RB ori kan r polylinker miniTi bom 1 bom = basis of mobilization
Alternate Methods of Transforming Plants: Particle Bombardment
One way of physically introducing DNA into cells is with a particlegun. Very tiny DNA-coated metal particles are suspended in a drop on a macroprojectile. A discharge (from a gunpowder explosion or from breakage of a membrane enclosing a pressurized chamber) impels the macroprojectile. pressurized chamber The macroprojectile is stopped by a stopping plate, but the microprojectiles continue into the tissue below. The DNA introduced with the particles is expressed