Comparative Genomics of Xanthomonas citri pv. citri A* Pathotype Reveals Three Distinct Clades with Varying Plasmid Distribution.

Citrus bacterial canker (CBC) is an important disease of citrus cultivars worldwide that causes blister-like lesions on host plants and leads to more severe symptoms such as plant defoliation and premature fruit drop. The causative agent, Xanthomonas citri pv. citri, exists as three pathotypes—A, A*, and Aw—which differ in their host range and elicited host response. To date, comparative analyses have been hampered by the lack of closed genomes for the A* pathotype. In this study, we sequenced and assembled six CBC isolates of pathotype A* using second- and third-generation sequencing technologies to produce complete, closed assemblies. Analysis of these genomes and reference A, A*, and Aw sequences revealed genetic groups within the A* pathotype. Investigation of accessory genomes revealed virulence factors, including type IV secretion systems and heavy metal resistance genes, differentiating the genetic groups. Genomic comparisons of closed genome assemblies also provided plasmid distribution information for the three genetic groups of A*. The genomes presented here complement existing closed genomes of A and Aw pathotypes that are publicly available and open opportunities to investigate the evolution of X. citri pv. citri and the virulence factors that contribute to this serious pathogen.