Molecular Signals Required for Type III Secretion and Translocation of the Xanthomonas campestris AvrBs2 Protein to Pepper Plants

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-11, Vol.97 (24), p.13324-13329
• Main Authors: Mudgett, Mary Beth, Chesnokova, Olga, Dahlbeck, Doug, Clark, Eszter T., Rossier, Ombeline, Bonas, Ulla, Staskawicz, Brian J.
• Format: Article
• Language: English
• Subjects: Agrobacterium; Agrobacterium tumefaciens - genetics; Arabidopsis - microbiology; Artificial Gene Fusion; avrBs2 gene; AvrBs2 protein; AvrRpt2 protein; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - physiology; Biological Sciences; Capsicum - microbiology; Cell death; Codons; Frameshift Mutation; Gene Deletion; Gene Transfer Techniques; hrp gene; Leaves; Messenger RNA; Mutagenesis; Peppers; Plant Leaves - microbiology; Plants; Plants, Medicinal; Polymerase Chain Reaction; Protein transport; Proteins; Pseudomonas - genetics; Pseudomonas syringae; Recombinant Fusion Proteins - metabolism; RNA, Messenger - genetics; Secretion; Signal Transduction; Transcription, Genetic; Xanthomonas campestris; Xanthomonas campestris - genetics; Xanthomonas campestris - pathogenicity; Xanthomonas campestris - physiology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.230450797

Strains of Xanthomonas campestris pv. vesicatoria (Xcv) carrying avrBs2 are specifically recognized by Bs2 pepper plants, resulting in localized cell death and plant resistance. Agrobacterium-mediated transient expression of the Xcv avrBs2 gene in plant cells results in Bs2-dependent cell death, indicating that the AvrBs2 protein alone is sufficient for the activation of disease resistance-mediated cell death in planta. We now provide evidence that AvrBs2 is secreted from Xcv and that secretion is type III (hrp) dependent. N- and C-terminal deletion analysis of AvrBs2 has identified the effector domain of AvrBs2 recognized by Bs2 pepper plants. By using a truncated Pseudomonas syringae AvrRpt2 effector reporter devoid of type III signal sequences, we have localized the minimal region of AvrBs2 required for type III secretion in Xcv. Furthermore, we have identified the region of AvrBs2 required for both type III secretion and translocation to host plants. The mapping of AvrBs2 sequences sufficient for type III delivery also revealed the presence of a potential mRNA secretion signal.