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''Agrobacterium tumefaciens'' (updated scientific name: ''Rhizobium radiobacter'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium.〔 Symptoms are caused by the insertion of a small segment of DNA (known as the T-DNA, for 'transfer DNA'), from a plasmid, into the plant cell, which is incorporated at a semi-random location into the plant genome. ''A. tumefaciens'' is an alphaproteobacterium of the family Rhizobiaceae, which includes the nitrogen-fixing legume symbionts. Unlike the nitrogen-fixing symbionts, tumor-producing ''Agrobacterium'' species are pathogenic and do not benefit the plant. The wide variety of plants affected by ''Agrobacterium'' makes it of great concern to the agriculture industry. Economically, ''A. tumefaciens'' is a serious pathogen of walnuts, grape vines, stone fruits, nut trees, sugar beets, horse radish, and rhubarb. ==Conjugation== To be virulent, the bacterium must contain a tumour-inducing plasmid (Ti plasmid or pTi), of 200 kb, which contains the T-DNA and all the genes necessary to transfer it to the plant cell. Many strains of ''A. tumefaciens'' do not contain a pTi. Since the Ti plasmid is essential to cause disease, prepenetration events in the rhizosphere occur to promote bacterial conjugation - exchange of plasmids amongst bacteria. In the presence of opines, ''A. tumefaciens'' produces a diffusible conjugation signal called 30C8HSL or the ''Agrobacterium'' autoinducer. This activates the transcription factor TraR, positively regulating the transcription of genes required for conjugation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Agrobacterium tumefaciens」の詳細全文を読む スポンサード リンク
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