@article{ZhangLeeWehneretal.2015,
  author    = {Zhang, Yi and Lee, Chil-Woo and Wehner, Nora and Imdahl, Fabian and Svetlana, Veselova and Weiste, Christoph and Dr{\"o}ge-Laser, Wolfgang and Deeken, Rosalia},
  title     = {Regulation of Oncogene Expression in T-DNA-Transformed Host Plant Cells},
  series = {PLoS Pathogens},
  volume    = {11},
  journal   = {PLoS Pathogens},
  number    = {1},
  doi       = {10.1371/journal.ppat.1004620},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-125256},
  pages     = {e1004620},
  year      = {2015},
  abstract  = {Virulent Agrobacterium tumefaciens strains integrate their T-DNA into the plant genome where the encoded agrobacterial oncogenes are expressed and cause crown gall disease. Essential for crown gall development are IaaH (indole-3-acetamide hydrolase), IaaM (tryptophan monooxygenase) and Ipt (isopentenyl transferase), which encode enzymes for the biosynthesis of auxin (IaaH, IaaM) and cytokinin (Ipt). Although these oncogenes are well studied as the tumor-inducing principle, nothing is known about the regulation of oncogene expression in plant cells. Our studies show that the intergenic regions (IGRs) between the coding sequences (CDS) of the three oncogenes function as promoters in plant cells. These promoters possess a eukaryotic sequence organization and cis-regulatory elements for the binding of plant transcription factors. WRKY18, WRKY40, WRKY60 and ARF5 were identified as activators of the Ipt promoter whereas IaaH and IaaM is constitutively expressed and no transcription factor further activates their promoters. Consistent with these results, the wrky triple mutant plants in particular, develops smaller crown galls than wild-type and exhibits a reduced Ipt transcription, despite the presence of an intact ARF5 gene. WRKY40 and WRKY60 gene expression is induced by A. tumefaciens within a few hours whereas the ARF5 gene is transcribed later during crown gall development. The WRKY proteins interact with ARF5 in the plant nucleus, but only WRKY40 together with ARF5 synergistically boosts the activation of the Ipt promoter in an auxin-dependent manner. From our data, we propose that A. tumefaciens initially induces WRKY40 gene expression as a pathogen defense response of the host cell. The WRKY protein is recruited to induce Ipt expression, which initiates cytokinin-dependent host cell division. With increasing auxin levels triggered by ubiquitous expression of IaaH and IaaM, ARF5 is activated and interacts with WRKY40 to potentiate Ipt expression and balance cytokinin and auxin levels for further cell proliferation.},
  language  = {en}
}
@phdthesis{Zhang2014,
  author    = {Zhang, Yi},
  title     = {Regulation of Agrobacterial Oncogene Expression in Host Plants},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-102578},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Virulent Agrobacterium tumefaciens strains transfer and integrate a DNA region of the tumor-inducing (Ti) plasmid, the T-DNA, into the plant genome and thereby cause crown gall disease. The most essential genes required for crown gall development are the T-DNA-encoded oncogenes, IaaH (indole-3-acetamide hydrolase), IaaM (tryptophan monooxygenase) for auxin, and Ipt (isopentenyl transferase) for cytokinin biosynthesis. When these oncogenes are expressed in the host cell, the levels of auxin and cytokinin increase and cause cell proliferation. The aim of this study was to unravel the molecular mechanisms, which regulate expression of the agrobacterial oncogenes in plant cells. Transcripts of the three oncogenes were expressed in Arabidopsis thaliana crown galls induced by A. tumefaciens strain C58 and the intergenic regions (IGRs) between their coding sequences (CDS) were proven to have promoter activity in plant cells. These promoters possess eukaryotic sequence structures and contain cis-regulatory elements for the binding of plant transcription factors. The high-throughput protoplast transactivation (PTA) system was used and identified the Arabidopsis thaliana transcription factors WRKY18, WRKY40, WRKY60 and ARF5 to activate the Ipt oncogene promoter. No transcription factor promoted the activity of the IaaH and IaaM promoters, despite the fact that the sequences contained binding elements for type B ARR transcription factors. Likewise, the treatment of Arabidopsis mesophyll protoplasts with cytokinin (trans-zeatin) and auxin (1-NAA) exerted no positive effect on IaaH and IaaM promoter activity. In contrast, the Ipt promoter strongly responded to a treatment with auxin and only modestly to cytokinin. The three Arabidopsis WRKYs play a role in crown gall development as the wrky mutants developed smaller crown galls than wild-type plants. The WRKY40 and WRKY60 genes responded very quickly to pathogen infection, two and four hours post infection, respectively. Transcription of the WRKY18 gene was induced upon buffer infiltration, which implicates a response to wounding. The three WRKY proteins interacted with ARF5 and with each other in the plant nucleus, but only WRKY40 together with ARF5 increased activation of the Ipt promoter. Moreover, ARF5 activated the Ipt promoter in an auxin-dependent manner. The severe developmental phenotype of the arf5 mutant prevented studies on crown gall development, nevertheless, the reduced crown gall growth on the transport inhibitor response 1 (TIR1) tir1 mutant, lacking the auxin sensor, suggested that auxin signaling is required for optimal crown gall development. In conclusion, A. tumefaciens recruits the pathogen defense related WRKY40 pathway to activate Ipt expression in T-DNA-transformed plant cells. IaaH and IaaM gene expression seems not to be controlled by transcriptional activators, but the increasing auxin levels are signaled via ARF5. The auxin-depended activation of ARF5 boosts expression of the Ipt gene in combination with WRKY40 to increase cytokinin levels and induce crown gall development.},
  subject      = {Agrobacterium tumefaciens},
  language  = {en}
}