Modulation of host defenses by the Type VI Secretion System (T6SS) of Agrobacterium tumefaciens
L. BANTA (1), M. Wang (2), A. Kenefick (2), B. Nguyen (2), J. Kim (2), R. Froom (2), A. Resnick (2), J. Bravo (1) (1) Williams College, U.S.A.; (2) Williams College, U.S.A.

In A. tumefaciens, as in several other bacteria species, the recently discovered type VI secretion system (T6SS) releases effectors that act as toxins in inter- and intra-bacterial competition. However, the contribution of the A. tumefaciens T6SS to virulence is not yet well understood. We discovered that Arabidopsis thaliana stem infections with agrobacteria lacking the T6SS resulted in the formation of fewer tumors than infections with wild type bacteria. This and other previous data have led us to hypothesize that the T6SS may dampen A. thaliana defenses, but in so doing, may inadvertently elicit host defenses as well. Using bacterial mutants deficient in one or more of the known T6SS effectors, we have begun to characterize the contributions of individual effectors to the attenuation and/or triggering of host responses. We have found that the T6SS impacts transient transformation as well as tumorigenesis. Other host responses that are altered include defense-related gene expression and resistance to subsequent infection by Pseudomonas syringae pv. maculicola. Investigations with mutant plant lines have revealed insights into the particular host defense pathways that may be modulated by the T6SS. Our data further suggest that the interplay between the host defenses and the bacterial T6SS is highly regulated and mutually antagonistic. Finally, consistent with our earlier observation that T6SS-deficient bacteria exhibit elevated biofilm formation, we have uncovered differential effects of specific T6SS effectors on bacterial motility.


Abstract Number: S5-2
Session Type: Special Session