last  page 39.768 Plant Molecular Genetics
Lecture 2, part 1 of 4		 next page

January 12, 2004

GENETIC ENGINEERING

I. Transformation methods

A. The Agrobacterium system

Crown gall disease

Discovery of transformation by A. tumefaciens

Mechanism of transformation

B. Transformation technology


 

I. TRANSFORMATION METHODS

A. The Agrobacterium system - History, physiology, biochemistry

Stumpf, P.K. and Conn, E.E. (Eds.in Chief) (1989) The Biochemistry of Plants: A Comprehensive Treatise, Vol. 15 "Molecular Biology" Abraham Marcus, Editor. Academic Press. Chapter 16. "Tumor Formation in Plants."

Agrios, G.N. (1978) Plant Pathology, 2nd. ed. Academic Press.

1. Crown gall disease

Affects woody and herbaceous plants belonging to 140 genera and more than 60 families. In nature, mostly on pome and stone fruit trees, brambles and grapes.
 
Agrobacterium tumefaciens Crown gall tumors on rose stems

 
A. tum. on peach root A. tum. on willow branch A. rubi on raspberry (cane gall)

[Agrios, Fig. 169 p485]
 

The superficial similarity between plant tumors and animal tumors was a strong impetus, in the 1970's, for the study of crown gall disease.

Click here for CROWN GALL DISEASE CYCLE (Agrios, p486, Fig.170)
 

Etiology
 

i) Small overgrowths in stem and roots, particularly near the soil line. Tumors usually originate in a wound.

ii) One or more foci of hyperplastic(1) cells appear in cortex or cambial layer, depending on depth of the wound.
 

1) Divide rapidly

2) Often multinucleate

3) Undifferentiated
 

iii) Tumors initially spherical, but outer tissues become convoluted and black or brown.

iv) Tumors are often connected to plant by a narrow neck of tissue. Bacteria are absent from the center of the tumors but can be found intercellularly in their periphery.

v) Mature tumors may contain vessels, or tracheids, which are unorganized and have little or no connection with the host's vascular system.

vi) Since tumor has no significant vascular connection to plant, tissue will rot and slough off. New tumors can re-form at same site in following year.
 

1. Hyperplastic - overgrowth due to increased cell division
 
 
last  page 39.768 Plant Molecular Genetics
Lecture 2, part 1 of 4		 next page