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 ?
Stenotrophomonas maltophilia, Sphingomonas paucimobilis, Rhizobium larrymoorei, Agrobacterium tumefaciens, Xanthomonas oryzae, and Pseudomonas aeruginosa.
Kalanchoe diagremontiana plants were infected with Agrobacterium tumefaciens, a bacterium that causes crown gall tumors to form in their wound sites.
Agrobacterium tumefaciens, an organism that causes tumors in plants, directs its host to make certain substances.
SRI International, a leading research institute based in Silicon Valley, today announced that it has used its Pathway Tools software to analyze a newly sequenced genome, Agrobacterium tumefaciens, producing a comprehensive database of its genome and computational analysis of its metabolic pathways.
MNH-93 (a good yielding local cotton variety but susceptible to lepidopterans insect pests) was transformed with Bacillus thuriengenesis gene (cry1Ab) using Agrobacterium tumefaciens strain C58[C.
Agrobacterium tumefaciens is a soil bacterium that has long been known to cause plant crown gall disease.
This assay utilizes a system based on the Crown Gall disease of plants caused by Agrobacterium tumefaciens.
An Agrobacterium tumefaciens bacterial host containing the plasmid construct can then be used to insert the desired sequence into the plant genome.
Crown gall disease is caused by the bacterium Agrobacterium tumefaciens that causes tumors on plant stems, and is the most common vector employed in plant genetic engineering.
in Research Triangle Park, North Carolina, was chosen for her key discoveries and wide-ranging contributions in the development of the Agrobacterium tumefaciens Ti plasmid as a major vector system for plant genetic engineering -- critical in transforming the genetic engineering of plants from science fiction to science fact.