Ti-Plasmid : Features, Diagram and Uses

Ti-Plasmid is also known as an extrachromosomal genetic material found in the plant pathogen Agrobacterium tumefaciens. The crown ball disease that affects dicot plants is caused by this phytopathogen. Numerous plant species have benefited from the Ti Plasmid’s use in transferring desired genes since its discovery in 1980.

The size of the Ti Plasmid is 200 kb. The bacteria Alphaproteobacteria contain the RepABC Plasmid family, of which the Ti Plasmid is a member. These are large plasmids that typically have a size between 100 kbp and 2 Mbp.

What is Ti-Plasmid?

Ti Plasmid is an extrachromosomal genetic material found in the dicot plant pathogen Agrobacterium tumefaciens. This phytopathogen causes crown ball disease, which is a problem for dicot plants. A useful tool for transferring desired genes to different plant species, the Ti Plasmid was initially discovered in 1980.

Nomenclature of Ti- Plasmid

The RepABC Plasmid family, which is present in Alphaproteobacteria, includes the Ti Plasmid. These Plasmids can range in size from 100 Kbps to 2 Mbps, which is often rather large. Because they only replicate at one spot, they are also frequently referred to as replicons. This family’s members carry the distinctive repABC gene cassette. The Ti-Plasmid was found by Mary-Dell Chilton and colleagues while investigating crown gall disease, which is brought on by the bacteria Agrobacterium tumefaciens. Ti-Plasmids such as pTiC58, pTiBo542, pTiA6NC, disarmed Ti-Plasmid, etc. are a few instances.

Structure of Ti-Plasmid

The following points elaborate on the structure of Ti-Plasmid:

• T-DNA region: This is the tumor-inducing region that carries the tumor-inducing gene, and it can be used to carry the gene of interest because this gene can migrate from one cell to another.
• Vir region: These genes are responsible for pathogenicity. T-DNA is transferred, integrated, and excised into the plant chromosome by it.
• Opine region: Opines are particular amino acids that are synthesised by T-DNA in bacteria. They are broken down and utilized as a source of carbon and nitrogen.
• Ti-Plasmid conjugation region: Important plant growth hormones, including auxins and cytokinins, are synthesized by the Ti-Plasmid conjugation region.
• Plant hormone synthesis region: Direct repetitions make up the 24-bp T-DNA border sequence. It is crucial for plant chromosomal transfer and denotes the boundary of T-DNA.

Types of Ti-Plasmid

Ti plasmids come in two varieties, distinguished by variations in their T-DNA region:

Nopaline

Its characteristics are:

•  It has a length of 25 kb.
• It has a continuous region of T-DNA.
• It is responsible for producing an amino acid known as Nopaline.

Octopine

Its characteristics are:

• In 1927, it was initially isolated from Octopus octopodia.
• It has two regions: one is 13 kb long, and the other is 8 kb long.
• It is responsible for producing an amino acid known as Octopine.

Features of Ti-Plasmid

Ti-Plasmid is considered to be a very important part of gene editing technology as it can be used to transfer the gene of interest. Here are some key features of it:

1. Tumor-causing genes: Plant crown gall disease is caused by the T gene, also known as the tumor-inducing gene, which is found in Ti-Plasmid and can spread from an individual cell to a subsequent one.
2. Vir gene or virulence gene: These genes are responsible for the pathogenicity of the bacterium and the perfect transfer of the bacterium into the host cell.
3. OriT: For T-DNA to successfully enter the host cell, a certain area is known as the origin of transfer.
4. Selectable marker genes: Ti-Plasmid consists of specific regions that can carry the gene of interest and can be transferred into the host cell.
5. Opine gene: Opines are the specific amino acids produced by the Ti-Plasmid.
6. Binary vector: Since the T-DNA and virulence portions of the Ti-Plasmid are different, it is possible to better regulate it by separating these parts.
7. Promoters and expression: The expression of a gene of interest is based on the promoter and expression region of Ti-Plasmid.

Uses of Ti-Plasmid

The following factors make Ti-Plasmid an excellent genetic engineering tool:

1. Ti-Plasmid are useful for producing Transgenic plants.
2. Restriction enzymes could be used to introduce and convert a desired gene into the plasmid.
3. It helps to produce plants that can withstand stress.
4. Ti Plasmid can also be used to introduce the nitrogen source and carbohydrate source into the plant as it produces opines.

Limitations of Ti-Plasmid

The following are the limitations of Ti-Plasmid:

1. Due to its large size, it can only be used for some experiments because other experiments need smaller vectors.
2. It cannot be used for monocot plants.
3. It is limited to usage on plants that are prone to infection by Agrobacterium.

FAQs- Ti-Plasmid

1. What is the size of Ti Plasmid? 

The size of the Ti (tumor-inducing) plasmid, which is commonly associated with Agrobacterium tumefaciens, can vary. However, the typical size range for Ti plasmids is around 200 to 250 kilobase pairs (kb).

2. What is the Ti Plasmid useful vector for?

The Ti Plasmid vector facilitates the introduction of DNA into plant cells without compromising their normal regeneration capacity.

3. Which bacteria is Ti Plasmid isolated from?

The Ti Plasmid is naturally found in Agrobacterium tumefaciens, a bacterium that transfers it to plant DNA, causing tumor formation.

4. What is the natural source of Ti Plasmid?

The natural source of the Ti (tumor-inducing) Plasmid is the bacterium Agrobacterium tumefaciens.

5. What are the limitations of Ti Plasmid?

Ti Plasmids in plant genetic engineering face limitations as its large DNA insert size results in restricted usage and it cannot be used in monocot plants.