Description:
<jats:p>
The plant pathogen
<jats:italic>Agrobacterium tumefaciens</jats:italic>
transforms plant cells by delivering its T-DNA into the plant cell nucleus where it integrates into the plant genome and causes tumor formation. A key role of VirE2-interacting protein 1 (VIP1) in the nuclear import of T-DNA during
<jats:italic>Agrobacterium</jats:italic>
-mediated plant transformation has been unravelled and VIP1 was shown to undergo nuclear localization upon phosphorylation by the mitogen-activated protein kinase MPK3. Here, we provide evidence that VIP1 encodes a functional bZIP transcription factor that stimulates stress-dependent gene expression by binding to VIP1 response elements (VREs), a DNA hexamer motif. VREs are overrepresented in promoters responding to activation of the MPK3 pathway such as
<jats:italic>Trxh8</jats:italic>
and
<jats:italic>MYB44.</jats:italic>
Accordingly, plants overexpressing VIP1 accumulate high levels of
<jats:italic>Trxh8</jats:italic>
and
<jats:italic>MYB44</jats:italic>
transcripts, whereas stress-induced expression of these genes is impaired in
<jats:italic>mpk3</jats:italic>
mutants.
<jats:italic>Trxh8</jats:italic>
and
<jats:italic>MYB44</jats:italic>
promoters are activated by VIP1 in a VRE-dependent manner. VIP1 strongly enhances expression from a synthetic promoter harboring multiple VRE copies and directly interacts with VREs in vitro and in vivo. Chromatin immunoprecipitation assays of the
<jats:italic>MYB44</jats:italic>
promoter confirm that VIP1 binding to VREs is enhanced under conditions of MPK3 pathway stimulation. These results provide molecular insight into the cellular mechanism of target gene regulation by the MPK3 pathway.
</jats:p>