Thursday, 6 August 2015

Agrobacterium tumefaciens and crown gall disease

Agrobacterium tumefaciens and crown gall disease

Introduction :

—                      1000’s of plant species are susceptible; they include especially rose, nut trees, grape, many shrubs and vines and perennial garden plants

Symptoms:
                       roundish, rough-surfaced galls, several inches or more in diameter, usually at or near the soil line, or on roots and lower stems
The galls,  at first cream coloured or greenish, later turn brown or black.
Crown gall, disease of plants caused by Agrobacterium tumefaciens.

           Avoiding replanting for that period; removing severely infected plants (including as many roots as possible); protecting against injury; keeping down weeds; controlling root-chewing insects and nematodes; cutting away large galls on trees, and disinfecting the wounds

Agrobacterium tumefaciens




Ti plasmid

  —The ability to cause crown gall disease is associated with the presence of the Ti 
     (tumorinducing) plasmid within the bacterial cell. This is a large (greater than 200 kb) plasmid
  —that carries numerous genes involved in the infective process
  —The ability to cause crown gall disease is associated with the presence of the Ti plasmid within the bacterial cell.
  —This is a large (greater than 200 kb) plasmid
That carries numerous genes involved in the infective process
  —This segment, called the T-DNA, is between 15 and 30 kb in size, depending on the strain.
  It is maintained in a stable form in the plant cell and is passed on to daughter cells as an integral part of the chromosomes
  —A remarkable feature of the Ti plasmid is that, after infection, part of the molecule is integrated into the plant chromosomal DNA 
 —But the most remarkable feature of the Ti plasmid is that the T-DNA contains eight or so genes that are expressed in the plant cell and are responsible for the cancerous properties of the transformed cells.
  —These genes also direct synthesis of unusual compounds, called opines, that the bacteria use as nutrients.
  —In short, A. tumefaciens genetically engineers the plant cell for its own purposes