Post-Transcriptional Gene Silencing of Agrobacterium tumefaciens Oncogenes

Speaker: Julie Law

Abstract:: Crown Gall Disease (CGD), which is caused by the soil bacterium
Agrobacterium tumefaciens, infects dicotyledonous plants and has become a
multimillion dollar problem in nurseries worldwide. The A.tumefaciens
bacterium causes CGD by integrating a portion of plasmid DNA into the host
plant. This portion of DNA contains the genes for isopentenyl
transferase (ipt) and tryptophan monooxygenase (iaaM). It is the
overproduction of these oncogenes causes the plant tumors associated with
The focus of this HHMI project is to silence the expression of the
two oncogenes of interest: ipt and iaaM, and thus the prevent CGD. The
method being used to achieve this goal-post transcriptional gene silencing
(PTGS)-is initiated by the presence of dsRNA of at least 70% homology to
the genes of interest.
The broad experimental procedure of this project begins with the
creation of a DNA construct, which contains inverted repeat copies of the
ipt and iaaM sequences identical to the A. tumefaciens oncogenes. The
inverted repeat structure will allow the formation of dsRNA upon
transcription by the plant host. Once the construct is built it will be
integrated into the chromosomes of Arabodopsis thailana plants, resulting
in a parent transgenic plant line. Subsequent generations of these parent
lines will then be treated with wild- type A. tumefaciens to test for
resistance to CGD.