Multiple Acquisitions of XopJ2 Effectors in Populations of <i>Xanthomonas perforans</i>

Type III effectors (T3Es) are major determinants of <i>Xanthomonas</i> virulence and targets for resistance breeding. XopJ2 (synonym AvrBsT) is a highly conserved YopJ-family T3E acquired by <i>X. perforans</i>, the pathogen responsible for bacterial spot disease of tomato. In this study, we characterized a new variant (XopJ2b) of XopJ2, which is predicted to have a similar three-dimensional (3D) structure as the canonical XopJ2 (XopJ2a) despite sharing only 70% sequence identity. XopJ2b carries an acetyltransferase domain and the critical residues required for its activity, and the positions of these residues are predicted to be conserved in the 3D structure of the proteins. We demonstrated that XopJ2b is a functional T3E and triggers a hypersensitive response (HR) when translocated into pepper cells. Like XopJ2a, XopJ2b triggers HR in <i>Arabidopsis</i> that is suppressed by the deacetylase, SOBER1. We found <i>xopJ2b</i> in genome sequences of <i>X. euvesicatoria</i>, <i>X. citri</i>, <i>X. guizotiae</i>, and <i>X. vasicola</i> strains, suggesting widespread horizontal transfer. In <i>X. perforans</i>, <i>xopJ2b</i> was present in strains collected in North America, Africa, Asia, Australia, and Europe, whereas <i>xopJ2a</i> had a narrower geographic distribution. This study expands the <i>Xanthomonas</i> T3E repertoire, demonstrates functional conservation in T3E evolution, and further supports the importance of XopJ2 in <i>X. perforans</i> fitness on tomato. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.