Transfer DNA

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Ti plasmid with tDNA region

The transfer DNA (abbreviated T-DNA) is the transferred

Agrobacterium rhizogenes (actually an Ri plasmid). The T-DNA is transferred from bacterium into the host plant's nuclear DNA genome.[1]
The capability of this specialized tumor-inducing (Ti) plasmid is attributed to two essential regions required for DNA transfer to the host cell. The T-DNA is bordered by 25-base-pair repeats on each end. Transfer is initiated at the right border and terminated at the left border and requires the vir genes of the Ti plasmid.

The bacterial T-DNA is about 24,000 base pairs long

opines are amino acid derivatives used by the bacterium as a source of carbon and energy. This natural process of horizontal gene transfer in plants is being utilized as a tool for fundamental and applied research in plant biology through Agrobacterium tumefaciens mediated foreign gene transformation and insertional mutagenesis.[5][6] Plant genomes can be engineered by use of Agrobacterium for the delivery of sequences hosted in T-DNA binary vectors
.

Mechanism of transformation in nature

The infection process of T-DNA into the host cell and integration into its nucleus involve multiple steps. First, the bacteria multiply in the wound sap before infection and then attach to the plant cell walls. The bacterial virulence genes expression of approximately 10

translocation from Agrobacterium to cytoplasm of host cell, transmission of T-DNA along with associated proteins (called T-complex) to the host cell nucleus followed by disassembly of the T-complex, stable integration of T-DNA into host plant genome, and eventual expression of the transferred genes. The integration of T-DNA into a host genome involves the formation of a single-stranded nick in the DNA at the right border of the Ti plasmid. This nick creates a region of single stranded DNA from the left border of the T-DNA gene over to the right border which was cut. Then, single stranded binding proteins attach to the single stranded DNA. DNA synthesis displaces the single stranded region and then a second nick at the left border region releases the single stranded T-DNA fragment. Further this fragment can be incorporated into a host genome.[7]

Agrobacterium has been known to evolve a control system that uses plant host factors and cellular processes for several pathways of host-plant defense response to invade the host cell nucleus. For the integration of T-DNA into the target host genome, Agrobacterium carries out multiple interactions with host-plant factors.[7] To interact with host plant proteins many Agrobacterium virulence proteins encoded by vir genes. Agrobacterium vir gene expression occurs via the VirA-VirG sensor that results in generation of a mobile single-stranded T-DNA copy (T-strand). A processed form of VirB2 is the major component of the T-complex that is required for transformation. VirD2 is the protein that caps the 5′ end of the transferred T-strand by covalent attachment and is transported to the host cell cytoplasm.[8][9] VirE2 is the single-stranded DNA binding protein that presumably coats the T- strand in the host cytoplasm by cooperative binding. It is then directed into the nucleus via interactions with the host cell proteins such as importin a, bacterial VirE3, and dynein-like proteins. Several other bacterial virulence effectors like VirB5, VirB7 (the minor components of the T-complex), VirD5, VirE2, VirE3, and VirF that may also interact with proteins of host plant cells.[10]

Uses in biotechnology

Agrobacterium-mediated T-DNA transfer is widely used as a tool in

dicotyledonous plants efficiently while taking care of critically important factors like the genotype of plants, types and ages of tissues inoculated, kind of vectors, strains of Agrobacterium, selection marker genes and selective agents, and various conditions of tissue culture.[4]

The same procedure of T-DNA transfer can be used to disrupt genes via

gene fusions in Arabidopsis thaliana.[15]

Reverse genetics involves testing the presumed function of a gene that is known by disrupting it and then looking for the effect of that induced mutation on the organismal phenotype. T-DNA tagging mutagenesis involves screening of populations by T-DNA insertional mutations. Collections of known T-DNA mutations provide resources to study the functions of individual genes, as developed for the model plant Arabidopsis thaliana.[16] Examples of T-DNA insertion mutations in Arabidopsis thaliana include those associated many classes of phenotypes including seedling-lethals, size variants, pigment variants, embryo-defectives, reduced-fertility, and morphologically or physiologically aberrant plants.[17]

See also

References

  1. PMID 28853920
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  2. S2CID 26118909
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  3. ISSN 0022-0957
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  4. ^
    S2CID 19196285
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  5. PMID 7770515
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  6. ^
    PMID 10590158
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  7. ^
    PMID 24166430
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  8. PMID 8380800
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  9. doi:10.13140/RG.2.2.18345.49769/1
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  10. PMID 12626681
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  11. PMID 20023148
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  12. PMID 18250230
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  13. S2CID 46196053
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  14. PMID 10339623
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  15. PMID 2554318
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  16. PMID 28217003
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  17. ISSN 1365-313X
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Further reading

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