Eukaryotic features of the Xanthomonas type III effector AvrBs3: protein domains involved in transcriptional activation and the interaction with nuclear import receptors from pepper.
The AvrBs3 protein of the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria is targeted to host-plant cells by the bacterial Hrp type III secretion system. In pepper plants containing the Bs3 resistance gene, AvrBs3 induces the hypersensitive response (HR). AvrBs3 recognition is thought to occur in the plant cell nucleus as HR induction is dependent on nuclear localization signals (NLSs) and an acidic transcription activation domain (AAD). In a search for AvrBs3-interacting pepper proteins using the yeast two-hybrid system, we have isolated eight different classes of cDNA inserts including two genes for importin alpha proteins. Importin alpha is part of the nuclear import machinery and interacts with AvrBs3 through an NLS in the carboxy-terminus of the protein, both in yeast and in vitro. The mechanism of AvrBs3 recognition was further studied by analysis of the C-terminal AAD. This putative transcription-activation domain was shown to be required for AvrBs3 HR-inducing activity, and could be functionally replaced with the VP16 AAD from the Herpes simplex virus. Our data support the model in which the AvrBs3 effector localizes to the nucleus, where the Bs3-mediated surveillance system of resistant plants detects AvrBs3 through its interference with host gene transcription.
Szurek
B
B
Institut für Genetik, Martin-Luther Universität Halle-Wittenberg, 06099 Halle, Germany.
Marois
E
E
Bonas
U
U
Van den Ackerveken
G
G
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D002212:Capsicum / Q000382:microbiology*; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D029543:Nucleocytoplasmic Transport Proteins / Q000378:metabolism*; D010935:Plant Diseases / Q000382:microbiology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D000071336:Transcription Activator-Like Effectors; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques; D016959:Xanthomonas campestris; D028901:alpha Karyopherins / Q000378:metabolism
D001426:Bacterial Proteins; D019913:Nuclear Localization Signals; D029543:Nucleocytoplasmic Transport Proteins; D000071336:Transcription Activator-Like Effectors; D014157:Transcription Factors; D028901:alpha Karyopherins; C073876:avrBs3-2 protein, Xanthomonas campestris