175. Vir genes are necessary for the transfer of the T-DNA into the host genome. The product of which one of the
following genes is tightly associated with the 5′ end of the T-strand and helps in nuclear targeting?
1. VirA
2. Vir G
3. Vir E
4. VirD2
Vir Genes and T-DNA Transfer
In genetic engineering, the transfer of the T-DNA (transfer DNA) from Agrobacterium tumefaciens into a host plant genome is a crucial step. This transfer process involves a set of Vir (virulence) genes, which are essential for the processing and integration of the T-DNA into the host DNA.
The T-DNA is part of the Ti plasmid (tumor-inducing plasmid) of Agrobacterium, and its transfer is mediated by a number of Vir genes. These genes enable the bacterium to recognize the plant host and facilitate the movement of the T-DNA into the plant’s nucleus.
Key Vir Genes Involved in T-DNA Transfer
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VirA: This gene encodes a sensor kinase that is involved in detecting plant signals, such as phenolic compounds, which trigger the activation of other Vir genes. VirA plays a role in initiating the transfer process.
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VirG: VirG is a response regulator that works in conjunction with VirA. When VirA is activated, it phosphorylates VirG, which then activates other Vir genes, including VirD2 and VirE.
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VirE: VirE is a protein that binds to the T-DNA and forms a protective complex, helping the T-DNA to be transferred to the host cell. This protein aids in stabilizing the T-DNA during the transfer process.
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VirD2: VirD2 is a critical protein that is tightly associated with the 5′ end of the T-strand (the single-stranded DNA that is transferred). It plays a vital role in the transfer process by helping the T-DNA to enter the plant cell and targeting the T-DNA to the nucleus.
VirD2 and Nuclear Targeting
The VirD2 protein is particularly important in ensuring that the T-DNA reaches the nucleus of the plant cell. It is tightly associated with the 5′ end of the T-strand and helps direct the T-DNA into the nucleus, where it can integrate into the plant’s genome. VirD2 contains a nuclear localization signal (NLS), which facilitates the import of the T-DNA-VirD2 complex into the plant nucleus.
Thus, the correct answer to the question is:
Correct Answer:
4. VirD2
VirD2 is the product that is tightly associated with the 5′ end of the T-strand and plays a crucial role in nuclear targeting during the T-DNA transfer process.
