Agrobacterium

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Agrobacterium
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Pseudomonadota
Class: Alphaproteobacteria
Order: Hyphomicrobiales
Family: Rhizobiaceae
Genus: Agrobacterium
Conn 1942 (Approved Lists 1980)
Type species
Agrobacterium radiobacter

(Smith and Townsend 1907) Conn 1942 (Approved Lists 1980)
Species
Synonyms[1]
  • Polymonas Lieske 1928

Agrobacterium is a

tumors in plants. Agrobacterium tumefaciens is the most commonly studied species in this genus. Agrobacterium is well known for its ability to transfer DNA between itself and plants, and for this reason it has become an important tool for genetic engineering
.

Nomenclatural History

Leading up to the 1990s, the genus Agrobacterium was used as a

chromid.[10] By this time, however, the three Agrobacterium biovars had become defunct; biovar 1 remained with Agrobacterium, biovar 2 was renamed Rhizobium rhizogenes, and biovar 3 was renamed Allorhizobium vitis
.

Plant pathogen

The large growths on these roots are galls induced by Agrobacterium sp.

T-DNA) from the bacterial tumour-inducing (Ti) plasmid. The closely related species, Agrobacterium rhizogenes, induces root tumors, and carries the distinct Ri (root-inducing) plasmid. Although the taxonomy of Agrobacterium is currently under revision it can be generalised that 3 biovars exist within the genus, Agrobacterium tumefaciens, Agrobacterium rhizogenes, and Agrobacterium vitis. Strains within Agrobacterium tumefaciens and Agrobacterium rhizogenes are known to be able to harbour either a Ti or Ri-plasmid, whilst strains of Agrobacterium vitis, generally restricted to grapevines, can harbour a Ti-plasmid. Non-Agrobacterium strains have been isolated from environmental samples which harbour a Ri-plasmid whilst laboratory studies have shown that non-Agrobacterium strains can also harbour a Ti-plasmid. Some environmental strains of Agrobacterium possess neither a Ti nor Ri-plasmid. These strains are avirulent.[11]

The plasmid T-DNA is integrated semi-randomly into the

selective advantage.[13]
By altering the hormone balance in the plant cell, the division of those cells cannot be controlled by the plant, and tumors form. The ratio of auxin to cytokinin produced by the tumor genes determines the morphology of the tumor (root-like, disorganized or shoot-like).

In humans

Although generally seen as an infection in plants, Agrobacterium can be responsible for opportunistic infections in humans with weakened immune systems,[14][15] but has not been shown to be a primary pathogen in otherwise healthy individuals. One of the earliest associations of human disease caused by Agrobacterium radiobacter was reported by Dr. J. R. Cain in Scotland (1988).[16] A later study suggested that Agrobacterium attaches to and genetically transforms several types of human cells by integrating its T-DNA into the human cell genome. The study was conducted using cultured human tissue and did not draw any conclusions regarding related biological activity in nature.[17]

Uses in biotechnology

See also: Horizontal gene transfer

The ability of Agrobacterium to transfer

plant improvement. Genomes of plants and fungi can be engineered by use of Agrobacterium for the delivery of sequences hosted in T-DNA binary vectors. A modified Ti or Ri plasmid can be used. The plasmid is 'disarmed' by deletion of the tumor inducing genes; the only essential parts of the T-DNA are its two small (25 base pair) border repeats, at least one of which is needed for plant transformation.[18][19] The genes to be introduced into the plant are cloned into a plant binary vector that contains the T-DNA region of the disarmed plasmid, together with a selectable marker (such as antibiotic resistance) to enable selection for plants that have been successfully transformed. Plants are grown on media containing antibiotic following transformation, and those that do not have the T-DNA integrated into their genome will die. An alternative method is agroinfiltration.[20][21]

Plant (S. chacoense) transformed using Agrobacterium. Transformed cells start forming calluses on the side of the leaf pieces

Transformation with Agrobacterium can be achieved in multiple ways. Protoplasts or alternatively leaf-discs can be incubated with the Agrobacterium and whole plants regenerated using plant tissue culture. In agroinfiltration the Agrobacterium may be injected directly into the leaf tissue of a plant. This method transforms only cells in immediate contact with the bacteria, and results in transient expression of plasmid DNA.[22]

Agroinfiltration is commonly used to transform tobacco (

gametes. The seeds can then be screened for antibiotic resistance (or another marker of interest). Plants that have not integrated the plasmid DNA will die when exposed to the antibiotic.[20]

Agrobacterium is listed as being the vector of genetic material that was transferred to these USA GMOs:[24]

The transformation of fungi using Agrobacterium is used primarily for research purposes,[25][26] and follows similar approaches as for plant transformation. The Ti plasmid system is modified to include DNA elements to select for transformed fungal strains, after co-incubation of Agrobacterium strains carrying these plasmids with fungal species.

Genomics

The sequencing of the genomes of several species of Agrobacterium has permitted the study of the evolutionary history of these organisms and has provided information on the genes and systems involved in pathogenesis, biological control and symbiosis. One important finding is the possibility that chromosomes are evolving from plasmids in many of these bacteria. Another discovery is that the diverse chromosomal structures in this group appear to be capable of supporting both symbiotic and pathogenic lifestyles. The availability of the genome sequences of Agrobacterium species will continue to increase, resulting in substantial insights into the function and evolutionary history of this group of plant-associated microbes.[27]

History

University of Ghent (Belgium) discovered the gene transfer mechanism between Agrobacterium and plants, which resulted in the development of methods to alter Agrobacterium into an efficient delivery system for gene engineering in plants.[18][19] A team of researchers led by Mary-Dell Chilton were the first to demonstrate that the virulence genes could be removed without adversely affecting the ability of Agrobacterium to insert its own DNA into the plant genome (1983).[28]

See also

References

  1. doi:10.1099/00207713-15-1-43
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  2. PMID 12501326
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  3. PMID 12501429
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  4. PMID 11211278
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  8. PMID 24581678
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  10. PMID 24440816
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  11. PMID 8240952
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  12. PMID 15659104
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  13. PMID 20150897
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  14. PMID 8448285
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  15. PMID 8408587
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  17. PMID 11172043
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  18. ^
    PMID 336023
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  19. ^
    PMID 16453483
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  20. ^ a b Thomson JA. "Genetic Engineering of Plants" (PDF). Biotechnology. 3. Archived (PDF) from the original on 17 January 2017. Retrieved 17 July 2016.
  21. PMID 23913006
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  22. PMID 24796351
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  23. S2CID 410286
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  24. ^ The FDA List of Completed Consultations on Bioengineered Foods Archived May 13, 2008, at the Wayback Machine
  25. S2CID 23959400
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  26. PMID 28955474
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  27. ISBN 978-1-904455-37-0
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  28. PMID 11154285
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Further reading

External links

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