Genomic Analysis of Xanthomonas oryzae Isolates from Rice Grown in the United States Reveals Substantial Divergence from Known X. oryzae Pathovars

ABSTRACTThe speciesXanthomonas oryzaeis comprised of two designated pathovars, both of which cause economically significant diseases of rice in Asia and Africa. AlthoughX. oryzaeis not considered endemic in the United States, anX. oryzae-like bacterium was isolated from U.S. rice and southern cutgrass in the late 1980s. The U.S. strains were weakly pathogenic and genetically distinct from characterizedX. oryzaepathovars. In the current study, a draft genome sequence from two U.S.Xanthomonasstrains revealed that the U.S. strains form a novel clade within theX. oryzaespecies, distinct from all strains known to cause significant yield loss. Comparative genome analysis revealed several putative gene clusters specific to the U.S. strains and supported previous reports that the U.S. strains lack transcriptional activator-like (TAL) effectors. In addition to phylogenetic and comparative analyses, the genome sequence was used for designing robust U.S. strain-specific primers, demonstrating the usefulness of a draft genome sequence in the rapid development of diagnostic tools.