crown gall

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crown gall:

see gallgall,
abnormal growth, or hypertrophy, of plant tissue produced by chemical or mechanical (e.g., the rubbing together of two branches) irritants or hormones. Chemical irritants are released by parasitic fungi, bacteria, nematode worms, gall insects, and mites.
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Crown gall

A neoplastic disease of primarily woody plants, although the disease can be reproduced in species representing more than 90 plant families. The disease results from infection of wounds by the free-living soil bacterium Agrobacterium tumefaciens which is commonly associated with the roots of plants.

The first step in the infection process is the site-specific attachment of the bacteria to the plant host. Up to half of the bacteria become attached to host cells after 2 h. At 1 or 2 weeks after infection, swellings and overgrowths take place in tissue surrounding the site of infection, and with time these tissues proliferate into large tumors (see illustration). If infection takes place around the main stem or trunk of woody hosts, continued tumor proliferation will cause girdling and may eventually kill the host. Crown gall is therefore economically important, particularly in nurseries where plant material for commercial use is propagated and disseminated.

Crown gall on peachenlarge picture
Crown gall on peach

Unlike healthy normal cells, crown gall tumor cells do not require an exogenous source of phytohormones (auxins and cytokinin) for growth in culture because they readily synthesize more than sufficient quantities for their own growth. They also synthesize basic amino acids, each conjugated with an organic acid, called opines. The tumor cells also grow about four times faster and are more permeable to metabolities than normal cells.

These cellular alterations, such as the synthesis of opines and phytohormone regulation, result from bacterial genes introduced into host plant cells by A. tumefaciens during infection. Although it is not understood how these genes are introduced into the plant cell, the genes for the utilization of these opines and for regulating phytohormone production have been found to be situated on an extrachromosomal element called the pTi plasmid. This plasmid, harbored in all tumor-causing Agrobacterium species, also carries the necessary genetic information for conferring the tumor-inducing and host-recognition properties of the bacterium.

Crown gall is consequently a result of this unique bacteria-plant interaction, whereby A. tumefaciens genetically engineers its host to produce undifferentiated growth in the form of a large tumor, in which there is the synthesis of a unique food source in the form of an opine for specific use by the bacterial pathogen. See Bacterial genetics, Genetic engineering, Plant hormones, Plant pathology

crown gall

[′krau̇n ‚gȯl]
(plant pathology)
A bacterial disease of many plants induced by Bacterium tumefaciens and marked by abnormal enlargement of the stem near the root crown.
References in periodicals archive ?
A combination of overgrowth control antibiotics improves Agrobacterium tumefaciens mediatd transformation efficiency for cultivated tomato (Lycopersicon esculentum M.
Agrobacterium tumefaciens - mediated genetic transformation of the entomopathogenic fungus Beauveria bassiana.
Optimisation de la transformation genetique de la ponme de terre par Agrobacterium tumefaciens.
Essas construcoes foram preparadas no plasmideo pCAMBIA2201, utilizado na transformacao genetica via Agrobacterium tumefaciens, e contendo promotores derivados de genes preferencialmente expressos no floema.
1995, "Transformation of The Wild Tomato Lycopersicon chilense Dun by Agrobacterium tumefaciens," Plant Cell Rep.
The plasmid of Agrobacterium tumefaciens naturally contains genes that integrate DNA elements in plant genomes.
Previous studies have shown that the dual promoter of Agrobacterium tumefaciens mannopine synthase (mas) genes is regulated by plant growth hormones, and that the activity of the mas dual promoters increases basipetally in developing plants; it has also been reported that the apical meristem contains a factor that inhibits stimulation of mas promoter activity (Langridge et al.
variety "Vitoria de Verao" were cut and cocultivated with recombinant Agrobacterium tumefaciens C58C1Rif[R] containing pG35SHBsAg or pG35SHBsAg[ER].
In addition, the present of coniferyl alcohol in PLBs, one of the phenolic compounds present in Dendrobium orchids which can induce vir gene expression in Agrobacterium tumefaciens and thus provides a fundamental element required for successful Agrobacterium -mediated transformation system in orchid plants (Nan et al, 1998).
2007) reportan la transformacion genetica del Agave salmiana a traves de dos tecnicas diferentes, cocultivo con Agrobacterium tumefaciens y bombardeo con microparticulas cargadas con ADN.
5 ml distilled water and 2 ml of 48-h old broth culture of Agrobacterium tumefaciens (approximately 5 x [10.