THE PLANT CELL, Vol 5, Issue 5 501-514, Copyright © 1993 by American Society of Plant Biologists
A Genetic Analysis of DNA Sequence Requirements for Dissociation State I Activity in Tobacco
J. English, K. Harrison and JDG. Jones
The Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich, NR4 7UH, United Kingdom
Our objective was to test whether the double Ds structure correlated with
Dissociation state I activity (i.e., high frequency of chromosome breakage
and low frequency of reversion) in maize exhibited similar properties in
tobacco. A genetic assay was established to test double Ds and related
structures for their ability to cause loss of the linked marker genes
streptomycin phosphotransferase and [beta]-glucuronidase in transgenic
tobacco. An engineered double Ds element and a simple Ds element showed
behavior consistent with that of state I and state II Ds elements,
respectively, as described for maize. DNA structural rearrangements
accompanied marker gene loss. Dissection of the double Ds structure showed
that a left end and a right end of Ds in direct orientation were sufficient
for the instability observed. This result suggested that left and right
ends of Ds in direct orientation can participate in aberrant transposition
events, consistent with two different models for double Ds-induced
chromosome breakage proposed previously. Both models predict that the
inversion of a half Ds element accompanies the aberrant transposition
event. Such an inversion was detected by polymerase chain reaction
experiments in tobacco and maize only when Activator activity was present
in the genome.