Crown gall disease is an agricultural problem caused by the soil-borne bacterium,
Agrobacterium tumefaciens. A. tumefaciens oncogenes cause transformed plant cells
to overproduce the hormones, auxin and cytokinin. High hormone levels cause
unorganized plant cell growth resulting in a gall. Control of crown gall disease is
difficult because after plant cell transformation has occurred, the bacterium is no
longer required for the disease to progress. Apple trees engineered to express double-stranded
RNA of two A. tumefaciens oncogenes, ipt and iaaM, silenced the expression
of the wild-type oncogenes and prevented crown gall disease. Only the iaaM
oncogene was targeted for posttranscriptional gene silencing (PTGS) as measured by
biological assays and by quantitative reverse-transcription polymerase chain reaction
(q-RTPCR) on transgenic tissue. However, if the translation initiation sequence of the
iaaM construction was eliminated, gall formation was not prevented, indicating that
translatable RNA initiates silencing whereas untranslatable RNA does not. Other data
indicate that the Arabidopsis thaliana micro-RNA pathway gene is involved in A.
tumefaciens-mediated tumorigenesis. A. thaliana plants with a mutation in HEN1, a
gene required for micro-RNA maturation, demonstrated a tenfold reduction in
tumorigenesis upon A. tumefaciens infection compared to wild-type. The same plant
line showed no difference in T-DNA transfer and nuclear uptake. / Graduation date: 2006
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29276 |
| Date | 06 June 2005 |
| Creators | Pitrak, Jennifer |
| Contributors | Ream, Walt |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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