Characterization of the functional duality of a bacterial type III secreted protein AvrRxo1 and its chaperone Arc1 as a toxin-antitoxin system
T. SHIDORE (1), J. Long (2), J. Leach (2), L. Triplett (1) (1) The Connecticut Agricultural Experiment Station, U.S.A.; (2) Colorado State University, U.S.A.

Toxin-Antitoxin (TA) systems are ubiquitous bacterial self-killing systems comprised of an antibacterial toxin and a neutralizing antitoxin. They are implicated in a variety of roles including plasmid maintenance, survival against stress, and killing bacterial competitors. AvrRxo1 is a type III effector of several plant pathogenic species of Xanthomonas, Burkholderia, and Acidovorax that triggers a hypersensitive response in the presence of the resistance protein Rxo1. The recently solved structure of AvrRxo1 and its binding partner Arc1 revealed its similarity to a Streptococcus TA system. In this study, a dual-plasmid validation assay was used to confirm that AvrRxo1:Arc1 is a functional TA system. Expression of avrRxo1 from five species demonstrated conservation of toxic activity across divergent homologs. Distribution analysis of the avrRxo1:arc1 operon in 185 strains of bacteria demonstrated complete conservation in some species, while others show a high frequency of avrRxo1 single-site inactivations that leave the arc1 gene intact. Expression of arc1 in E. coli positively influenced growth, suggestive of a selective advantage in bacteria. Five avrRxo1:arc1-like modules were also identified in genomes of diverse nonpathogenic soil-inhabiting species, and the role of avrRxo1:arc1 cloned from a Myxobacterium was investigated. This work demonstrates that a secreted effector may have a dual role as a TA toxin. 

Abstract Number: P9-307
Session Type: Poster