title: Regulation of oncogene expression in T-DNA-transformed host plant cells.
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.
authors.affiliation: Julius-von-Sachs-Institute, Department of Molecular Plant Physiology and Biophysics, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Leibniz Institute of Plant Biochemistry, Halle /Saale, Germany.
authors.forename: Chil-Woo
authors.initials: CW
authors.lastname: Lee
authors.affiliation: Julius-von-Sachs-Institute, Pharmaceutical Biology, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Nora
authors.initials: N
authors.lastname: Wehner
authors.affiliation: Julius-von-Sachs-Institute, Department of Molecular Plant Physiology and Biophysics, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Imdahl
authors.affiliation: Institute of Biochemistry and Genetics, Ufa Scientific Centre of Russian Academy of Sciences, Ufa, Russia.
authors.forename: Veselova
authors.initials: V
authors.lastname: Svetlana
authors.affiliation: Julius-von-Sachs-Institute, Pharmaceutical Biology, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Weiste
authors.affiliation: Julius-von-Sachs-Institute, Pharmaceutical Biology, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Dröge-Laser
authors.affiliation: Julius-von-Sachs-Institute, Department of Molecular Plant Physiology and Biophysics, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Rosalia
authors.initials: R
authors.lastname: Deeken
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics*; D017360:Arabidopsis / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002461:Cell Line, Transformed; D018506:Gene Expression Regulation, Plant; D054884:Host-Pathogen Interactions / Q000235:genetics; D008969:Molecular Sequence Data; D015513:Oncogene Proteins / Q000235:genetics*; D009857:Oncogenes / Q000235:genetics*; D030821:Plants, Genetically Modified; D014170:Transformation, Genetic
chemical_list: D001426:Bacterial Proteins; C112234:LSO protein, Agrobacterium tumefaciens; D015513:Oncogene Proteins