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. 2015 Jan 23;11(1):e1004620. doi: 10.1371/journal.ppat.1004620

Figure 8. Proposed model on the regulation of oncogene expression in host cells.

Figure 8

(A) The plant cells have low auxin levels at the early stage of transformation by A. tumefaciens. The bidirectional promoter between CDSs of IaaH and IaaM is recognized by RNA polymerase II complex (RNAP II) to induce basal levels of transcription. Under low auxin conditions, the transcriptional activity of ARF5 is largely blocked by IAA12 via the interaction of domain III and IV. The transcription factor WRKY40 binds to W-boxes (TGAC) located in the Ipt promoter and activates transcription of the Ipt gene. (B) T-DNA transformed plant cells contain elevated auxin levels six days after inoculation due to the constitutive activity of the IaaH and IaaM enzymes and secretion by A. tumefaciens cells. High concentration of auxin mediates the interaction between TIR1 and IAA12. Poly-ubiquitination of IAA12 by the complex of TIR1, SKP (ASK1) and cullin1 (CUL1) induces its degradation and releases ARF5 to bind to the AuxREs (TGTCNC or TGTCTN) in the Ipt promoter and form a complex with WRKY40 via domain III and IV. The ARF5-WRKY40 complex finally potentiates activation of the Ipt promoter and promotes expression of the Ipt oncogene.