title: Visualization of novel virulence activities of the Xanthomonas type III effectors AvrBs1, AvrBs3 and AvrBs4.
abstract: Xanthomonas campestris pv. vesicatoria secretes at least 20 effector proteins through the type III secretion system directly into plant cells. In this study, we uncovered virulence activities of the effector proteins AvrBs1, AvrBs3 and AvrBs4 using Agrobacterium-mediated transient expression of the corresponding genes in Nicotiana benthamiana, followed by microscopic analyses. We showed that, in addition to the nuclear-localized AvrBs3, the effector AvrBs1, which localizes to the plant cell cytoplasm, also induces a morphological change in mesophyll cells. Comparative analyses revealed that avrBs3-expressing plant cells contain highly active nuclei. Furthermore, plant cells expressing avrBs3 or avrBs1 show a decrease in the starch content in chloroplasts and an increased number of vesicles, indicating an enlargement of the central vacuole and the cell wall. Both AvrBs1 and AvrBs3 cause an increased ion efflux when expressed in N. benthamiana. By contrast, expression of the avrBs3 homologue avrBs4 leads to large catalase crystals in peroxisomes, suggesting a possible virulence function of AvrBs4 in the suppression of the plant defence responses. Taken together, our data show that microscopic inspection can uncover subtle and novel virulence activities of type III effector proteins.
authors.affiliation: Institute of Biology, Department of Genetics, Martin-Luther-University Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Germany. d.guerlebeck@gmx.net
authors.forename: Doreen
authors.initials: D
authors.lastname: Gürlebeck
authors.forename: Simone
authors.initials: S
authors.lastname: Jahn
authors.forename: Norman
authors.initials: N
authors.lastname: Gürlebeck
authors.forename: Robert
authors.initials: R
authors.lastname: Szczesny
authors.forename: Boris
authors.initials: B
authors.lastname: Szurek
authors.forename: Simone
authors.initials: S
authors.lastname: Hahn
authors.forename: Gerd
authors.initials: G
authors.lastname: Hause
authors.forename: Ulla
authors.initials: U
authors.lastname: Bonas
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000648:ultrastructure; D007477:Ions; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000166:cytology / Q000382:microbiology / Q000648:ultrastructure; D021381:Protein Transport; D013347:Subcellular Fractions / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000382:microbiology / Q000648:ultrastructure; D014158:Transcription, Genetic; D014617:Vacuoles / Q000648:ultrastructure; D014774:Virulence; D014974:Xanthomonas / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; D007477:Ions