Xanthomonas citri pv. citri Genome sequencing and assembly

In 2015, backyard lime (Citrus spp.) trees in Texas exhibiting typical citrus canker symptoms were confirmed positive for Xanthomonas citri subsp. citri. This confirmation triggered a USDA regulatory response since the disease was absent from the state since 1940s. Rapid determination of the potential host range capacity of the strains was an important goal. The complete genomes of three strains isolated from infected trees in Texas were determined. Bioinformatic analyses indicated that the new strains were highly related to the Wellington (AW) strain group previously found in Florida, which are limited in host range to Mexican lime. However, all three Texas strains carried nearly identical and unusual large plasmids, significant fragments of which were found in contigs of unfinished genomes WGS database from some X. citri subsp citri, X. fuscans pv. fuscans and X. axonopodis pv. manihotis strains, which attack cassava plants. These plasmids contain a region of ca. 39 kB similar to Type 4 conjugational transfer genes, indicating potential for horizontal transfer. The predicted host range and pathogenicity effector repertoire was consistent with the observed AW phenotypic pathotype of these strains. No genes encoding additional potential effectors were identified on any the large plasmids.