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 ?
The possibility that the mechanism of transfer of DNA from the bacterium to the plant cell in crown gall disease is similar to the conjugative system in bacteria was noted in early studies (Binns & Thomashow, 1988).
As in the case of crown gall disease, there is a transfer of genetic material from a plasmid of the infecting organism, A.
The study of crown gall disease in plant stems is important, not only because of its long history but also because the present knowledge of the disease is based on a large number of disciplines and organisms: microbiology (bacteriology), plant physiology, plant and bacterial biochemistry, genetics and molecular genetics, transgenic plants and crops, and disease and evolutionary history.
Crown gall and its related adventitious root disease are still an unfinished and fascinating story.
Cellular transformation in crown gall. Pp.823-831 in H.
Agrobacterium-induced crown gall and hairy root diseases: Their biology and application to plant genetic engineering.
(1979) Agrobacterium radiobacter strain 84 and biological control of crown gall. Annu.
(2000) Use of the Genetically Engineered Agrobacterium Strain K1026 for Biological Control of Crown Gall. Eur.
(1980) Biological control of crown gall through production of agrocin 84.
(2005) Inhibition of crown gall formation by Agrobacterium radiobacter biovar 3 strains isolated from grapevine.
(2007) Biological control of grapevine crown gall by nonpathogenic Agrobacterium vitis strain VAR03-1.
(2008) Biological control of crown gall of grapevine, rose, and tomato by nonpathogenic Agrobacterium vitis strain VAR03-1.