P-300 - Role of plasmid-mediated horizontal gene transfer in the evolution of Xanthomonas euvesicatoria pv. perforans, a bacterial spot pathogen

The emergence of Xanthomonas euvesicatoria pv. perforans (Xep) as a dominant tomato pathogen, displacing the other bacterial spot pathogen X. euvesicatoria pv. euvesicatoria, indicates its remarkable evolutionary success. Plasmids are key drivers of horizontal gene transfer that facilitate bacterial evolution in a multi-faceted manner. We investigated plasmid diversity, their gene content, and distribution in relation to chromosomal phylogeny across a large collection of Xep genomes from different geographical locations to obtain a global overview of Xep plasmidome. We identified distinct plasmid cliques through a network approach based on shared k-mer content, which were confined to specific phylogenetic clusters supporting potential incompatibility or restricted plasmid movement between them. These plasmid cliques harbor virulence genes encoding type III secretion effectors, including transcriptional activator-like effectors, as well as genes associated with biocide resistance, such as copper resistance. This study revealed gene reshuffling between plasmids, facilitated by transposons encompassing regions carrying type III secretion effector genes and copper resistance genes. These findings provide foundational insights into the role of mobile genetic elements in the evolution and diversification of a bacterial spot pathogen, enhancing our understanding of the risks associated with continued adaptation, increased aggressiveness, and resistance to bactericides.