indirect mode of gene tranfer
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Transcript of indirect mode of gene tranfer
Gene transfer methods in plants Transformation :- Transfer of desirable gene from one plant species to another Transgene : Transferred gene Transgenic plant : Transformed plantReasons for developing transgenic plants :-To improve the agriculture , horticulture or
ornamental value of plantsTo study the action of gene in plants during
development & various biological process
To develop plant bioreactors for inexpensive manufacture of commercially important products
e.g:- proteins , medicine , pharmaceutical compoundGenetic traits introduced into plants :-• Resistance to herbicides• Protection against viral infections• Insecticidal activity• Improved nutritional quality • Altered flower pigmentation • Tolerance to environmental stresses• Self incompatibility
Gene transfer techniques:-The gene transfer technique in plant genetic transformation is broadly divided in two categories :- 1.Vector mediated / indirect gene
transfer2.Vector less mediated / direct
gene transfer
Vector mediated :-Carried by agrobacterium or by use of plant virus as vectors
Most vectors carried marker genes which allow recognition of transformed cells – selectable markers
E.g:- npt is a common selectable marker providing kanamycin resistance Common features of vectors :-1. Multiple unique restriction sites2. Ori
Agrobacterium ti plasmid is preferred all over other vectors because of wide range & capacity to transfer genes due to presence of T DNA border sequence
Agrobacterium mediated gene transfer :-soil born gram negative bacterium Rod shaped Family – rhizobiaceae A natural genetic eng capable of integrating its DNA into plant genome
Species of agrobacterium :- A. tumefaciens - crown gall disease A. rhizogenes - hairy root disease Characteristics of ti plasmid :-200 kb plasmid Varying length of 12 – 24 kb 4 major regions • T DNA region • An ori• Virulence region • Opine catabolism region
T DNA region is a part of Ti plasmid it can be integrated in to the plant genome . T DNA has right & left borders
Virulence region genes helpful for T DNA transfer in to plant genome . Mutations in this region abolishes virulence
The opine catabolism region synthesis opine
Ori is responsible for replication
General structure of T DNA :- T DNA consists of 1.Onc (oncogenisity region) :-Onc region consists of tms 1 & tms 2 , tmr These are responsible for biosynthesis of 2 phytohormones namely IAA , isopentyl adenosine 5ˡ monophosphate ( cytokine )
These genes causes crown gall disease2.Nos region :-Responsible for the synthesis of aa or sugar derivatives called opines
Depending upon opine, the bacteria is octopine type or nopaline type
Virulence region :-Organized in to 6 operons ( a,b,c,d,e,g )A,B,D,G – required for virulence C,E – tumor formationA - located on the inner membrane of bacteria . Chemoreceptor for plant hormones
B - form a pore between bacteria & plant cell
D - cutting of T DNA E - preventing degradation of T DNA , covers T DNA
G - induces all virulence gene
Mechanism of T DNA transfer
production of acetosyrengone binding of bacteria to plant cell vir genes activated by phenolic compounds vir A & vir G & all vir genes are activated vir D cleaves T DNA tube formed between bacteria & plant cell DNA is transferred in to plant cell Recombination occurs
Production of dis armed Ti plasmid:- In T DNA the genes b/w the L&R border are removed
Any fragment can be transformed in to plant genome by replacing T DNA with our gene of interest
Prerequisites• L&R borders • Vir genes • Chromosomal genes
Hairy root disease A.rhizogenes infect plants results in hairy
root . These plasmids are referred as Ri plasmids
Some of these Ri plasmids posses genes that are homologous to Ti plasmid
e.g:- auxin biosynthetic genesInstead of virulence genes Ri plasmid
contains a series of open reading frames on TDNA
Hairy root system are used in the production of secondary metabolites particularly pharmaceutical products
Advantages :-Natural method of gene transferAgrobacterium can conveniently infect any
explantLarge fragment of DNA can be effectively
transferredTransformed plant can be effectively
regenerated
Limitations:-Extensively utilized for dicotyledonous species monocotyledons could not be successfully utilized for agrobacterium gene transfer(failure of gene response in monocotyledons)
Cells that regenerate more efficiently are often difficult to transformed
Deep layers are not easy target