In nature, Agrobacterium tumefaciens is a bacterium that infects the roots and stems of plants and causes the disease crown gall (bacterial tumor). The bacterium inserts into the plant root cell genes for the production of cytokinin and auxin, which are plant hormones. This will lead to a lot of cell division and growth from the infected plant cell. This can further lead to the plant disease crown gall. The cytokinin and auxin genes are found on a small plasmid (a circular strand of DNA) that the bacterium can introduce into a plant cell. By exploiting this bacterial ability to transfer foreign genes into the host cell, Agrobacterium has become a very important tool for genetic engineering.
Agrobacterium-mediated gene transfer has been used to genetically modify many different crops around the world. The plasmid is cut open with enzymes used in biotechnology to cut the DNA where it is desired. The desired gene for introduction into the host plant is then inserted. The modified Agrobacterium can divide cells and form a bacterial culture with an inserted gene for transfer into cells from the plant that will receive the gene.
Agrobacterium-mediated gene transfer is a process in which foreign genes are inserted into cell tissue cultures to form a plant with new characteristics. New traits such as insect resistance or herbicide tolerance are those most often introduced into crops. Genetically modified dicotyledonous plants such as soya e.g. MON 87708, oilseed rape e.g. MON 88302, cotton e.g. GHB614 and many other genetically modified crops have been developed using Agrobacterium.
Agrobacterium-mediated gene transfer is also successful with monocots such as maize, e.g. NK603. Technological development in Agrobacterium-mediated gene transfer has in recent years led to cell tissue cultures of other monocotyledonous plants also becoming possible to modify with genes selected from bacterial cultures such as rice, barley, wheat and sugar cane. Agrobacterium-mediated gene transfer is the most commonly used method for the transfer of gene modifications.
Potential germ cells from the plant for genetic modification, e.g. Excisions of plant leaves are placed on a plant germination culture in a petri dish. These cuttings are then infected with cell culture with Agrobacterium with the plasmid with the gene inserted for transfer to plant cells. The genetically modified cells that can grow are stimulated with various growth promoting substances. Plant shoot promoting agents are used to make the genetically modified cells develop fences (shoot induction). Where fences have grown (extension), these can be placed on a medium with plant root promoters to make the cells develop roots (root induction). The plant is grown with genetic modification into an adult plant with genetically modified seeds.
Agrobacterium tumefaciens, which is used for gene transfer by GMO producers, has been changed to get better results in the gene modification process. The genes that lead to crown gall disease have been removed. This is to prevent it from being infected with crown gall. Despite all controls, the genetically modified plants can carry genes that are different from what was intended by the producers. Genes for insect resistance can e.g. become slightly shorter where they are taken up in plant chromosomes. Small changes in a gene can lead to large changes in the properties of the protein it codes for, e.g. altered toxicity. The cell biology of the host plant's cell biology can also significantly change the expression of the inserted gene in an unpredictable way.
Link:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5323423/pdf/fpls-08-00246.pdf
Reference:
Koetle MJ, Finnie JF, Balázs E., and J. Van Staden. 2015. A review on factors affecting the Agrobacterium-mediated genetic transformation in ornamental monocotyledonous geophytes. South African Journal of Botany 98, 37-44.
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