A T-DNA binary system is a pair of plasmids consisting of a binary plasmid and a helper plasmid. The two plasmids are used together to produce genetically modified plants

Genetically modified plant

Genetically modified plants are plants whose DNA is modified using genetic engineering techniques. In most cases the aim is to introduce a new trait to the plant which does not occur naturally in this species...

. They are artificial vectors

Vector (molecular biology)

In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell. The four major types of vectors are plasmids, viruses, cosmids, and artificial chromosomes...

 that have both been created from the naturally occurring Ti plasmid

Ti plasmid

Ti plasmid is a circular plasmid that often, but not always, is a part of the genetic equipment that Agrobacterium tumefaciens and Agrobacterium rhizogenes use to transduce its genetic material to plants. Ti stands for tumor inducing. The Ti plasmid is lost when Agrobacterium is grown above 28°C....

 found in Agrobacterium tumefaciens

Agrobacterium tumefaciens

Agrobacterium tumefaciens is the causal agent of crown gall disease in over 140 species of dicot. It is a rod shaped, Gram negative soil bacterium...

. The binary vector is able to replicate

DNA replication

DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...

 in both E. coli and Agrobacterium tumefaciens

Agrobacterium tumefaciens

Agrobacterium tumefaciens is the causal agent of crown gall disease in over 140 species of dicot. It is a rod shaped, Gram negative soil bacterium...

.

Systems in which T-DNA and vir genes are located on separate replicons are called T-DNA binary systems. T-DNA is located on the binary vector (the non-T-DNA region of this vector containing origin(s) of replication that could function both in E. coli and in Agrobacterium tumefaciens

Agrobacterium tumefaciens

Agrobacterium tumefaciens is the causal agent of crown gall disease in over 140 species of dicot. It is a rod shaped, Gram negative soil bacterium...

, and antibiotic-resistance genes used to select for the presence
of the binary vector in bacteria, became known as vector backbone sequences). The replicon containing the vir genes became known as the vir helper. Strains harboring this replicon and a T-DNA are considered disarmed if they do not contain oncogenes that could
be transferred to a plant.

There are several binary vector systems that differ mainly in the plasmid

Plasmid

In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...

 region that facilitates replication in Agrobacterium

Agrobacterium

Agrobacterium is a genus of Gram-negative bacteria established by H. J. Conn that uses horizontal gene transfer to cause tumors in plants. Agrobacterium tumefaciens is the most commonly studied species in this genus...

. Commonly used binary vectors include:

• pBIN19
• pPVP
• pGreen
  PGreen
  The pGreen plasmids were first described in 2000. The supporting web page provides supplementary information and ongoing support to researchers to request their plasmid resources...
  
  

Reference

• T-DNA Binary Vectors and Systems
• Lan-Ying Lee and Stanton B. Gelvin*
• Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907–1392