P-169 - Type II Effectors: An Underappreciated Bacterial Arsenal

Gram-negative phytopathogens utilize a multi-secretion system strategy to deploy diverse virulence factors into plants, where they engineer the apoplast as a niche for their multiplication. The molecular battle between plants and bacterial has been extensively characterized via the study of type III secreted effectors (T3Es), revealing mechanisms of pathogenesis and immunity. However, our research demonstrates that the understudied type II secretion system (T2SS) contributes equally to virulence in tomato-infecting Xanthomonas, releasing proteins into the apoplast where they modify the bacterial microenvironment and promote disease. The T2SS is a conserved virulence-relevant feature among a range devastating phytopathogens including Xanthomonas, Pseudomonas, Ralstonia, Erwinia, Dickeya, Pectobacterium, and Xylella, yet we lack knowledge of which T2Es are required for pathogenesis and their molecular functions. We will present our proteomics approach for the identification of virulence-relevant type II-secreted effectors (T2Es) and reveal one role of T2E-mediated plant cell wall degradation in pathogenesis. Given the widespread conservation of the T2SS and some T2Es among prevalent phytopathogens, some of which lack the T3SS entirely, elucidating T2E functions will generate insights applicable beyond xanthomonads.