<p><i>Agrobacterium
tumefaciens </i>transfers
virulence effector proteins to infected host plants to facilitate the transfer
and trafficking of a piece of its tumor inducing (Ti) plasmid, (T-[transfer]
DNA), into and through plant cells.<sup> </sup>T-DNA integrates into the host
genome where it uses the host’s gene expression machinery to express
transgenes. Scientists have used this process to insert beneficial genes into
plants by replacing native T-DNA in the bacteria with engineered T-DNA, making <i>Agrobacterium</i>-mediated transformation
the preferred method for crop genetic engineering. In spite of its wide-spread use in research and agriculture, we still do
not have a complete understanding of the transformation process. Consequently,
many important crop species remain highly resistant to transformation. One of
my lab’s major goals is to define the molecular interactions between <i>Agrobacterium</i> and its host plants which
mediate transformation. I study the role of the <i>Agrobacterium</i> effector protein, VirE2, which is important for plant
transformation. VirE2 likely coats the transferred DNA (T-DNA) after it enters
the plant cell and protects it from degradation. VIP1 is a host transcription
factor that interacts with VirE2 and is involved in activating plant defense
responses. VIP1 localizes to both the cytoplasm and the nucleus.<sup> </sup>Under
stress, VIP1 localizes to the nucleus where it activates expression of defense
response genes.<sup> </sup>This observation led to the model that T-DNA-bound
VirE2 binds VIP1 and uses VIP1 nuclear localization to deliver T-DNA into the
nucleus (the “Trojan Horse” model). In contrast to this model, our lab has
obtained data showing that VirE2 holds at least a portion of the VIP1 pool
outside the nucleus. We also showed that VIP1 and its homologs are not
necessary for transformation. VirE2 interacts with several host proteins in
addition to VIP1, and these interactions could lead to changes in host gene
expression and protein levels, possibly facilitating transformation. We
investigated this model by placing VirE2 under the control of an inducible
promoter in <i>Arabidopsis</i> and
performing RNA-seq and proteomics under non-induced and induced conditions, and
in the presence of <i>Agrobacterium</i> to
determine its individual effect on plant RNA and protein levels during
infection. Some genes differentially expressed after VirE2 induction are known
to be important for transformation. Knockout mutant lines of some VirE2
differentially expressed genes showed altered transformation phenotypes.
Protein levels of genes known to be important for transformation were also
increased in response to VirE2 induction, and overexpression of some of these
genes resulted in increased transformation susceptibility. We therefore
conclude that VirE2 modulates both plant RNA and protein levels to facilitate transformation.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8273699 |
| Date | 14 August 2019 |
| Creators | Rachelle Amanda Lapham (6838424) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Novel_Role_of_the_Agrobacterium_Virulence_Effector_Protein_VirE2_in_Modulating_Plant_Gene_Expression/8273699 |
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