Contribution of type III/TAL effectors to pathogenicity
J. Boch (1), T. Boureau (2), C. Brin (2), S. Cunnac (3), P. David (2), J. X. Feng (4), A. Hajri (2), M. Hutin (3), R. KOEBNIK (3), W. L. Mo (4), C. Pesce (3), S. Poussier (5), J. Streubel (1), B. Szurek (3), J. L. Tang (4), W. Tang (4), T. T. Tran (3), V.. (1) INRA/CNRS University Toulouse 3, Castanet Tolosan, France; (2) INRA/CNRS, Castanet Tolosan, France
Most plant-pathogenic bacteria use a sophisticated protein delivery device to inject type III effectors (T3Es) into the host’s cells for the benefit of the pathogen. The <i>French Network on Xanthomonads</i> studies several species of <i>Xanthomonas</i> and examines the role of T3Es during the infection process. Here, we will focus on two rice pathogens, <i>X. oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>) and <i>X. oryzae</i> pv. <i>oryzicola</i> (<i>Xoc</i>). First, the diversity within T3E repertoires of 45 strains clearly showed that both pathogens belong to closely related, but distinct, phylogenetic groups. Both pathogens comprise core and variable T3E suites that probably have distinct roles in pathogenicity and different evolutionary histories. We examined whether or not one of the differential T3Es between <i>Xoo</i> and <i>Xoc</i>, XopO, acts as a determinant of tissue specificity. Second, we monitored 41 candidate <i>Xoo</i> T3Es for their ability to translocate an AvrBs1 reporter into plant cells. Nine proteins were identified as <i>bona fide</i> T3Es. Mutations in their genes revealed that one of them, <i>xopR</i>, contributes to virulence in hybrid rice. Third, we isolated a new TAL effector that induces a rice <i>SWEET</i> gene to promote colonization of the leaf blades. Artificial <i>TAL</i> genes were then used to systematically evaluate the potential of <i>SWEET</i> genes to support the growth of <i>Xoo</i> in the xylem vessel. Only five phylogenetically close SWEET proteins which presumably act as sucrose transporters were found to provoke virulence.
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