Novel genetic traits inXanthomonasunveiled by the complete genome sequencing of three clade-1 xanthomonads

Abstract

ABSTRACTEvolutionary early-branching xanthomonads, also referred to as clade-1 xanthomonads, include major plant pathogens, most of which colonize monocotyledonous plants. Seven species have been validly described, among them the two sugarcane pathogensXanthomonas albilineansandXanthomonas sacchari, andXanthomonas translucens, which infects small grain cereals, diverse grasses, but also asparagus and pistachio trees. Single-gene sequencing and genomic approaches indicated that this clade likely contains more, yet undescribed species. In this study, we sequenced representative strains of three novel species using long-read sequencing technology.Xanthomonassp. pv.phormiicolastrain CFBP 8444 causes bacterial streak on New Zealand flax, another monocotyledonous plant.Xanthomonassp. strain CFBP 8443 has been isolated from common bean andXanthomonassp. strain CFBP 8445 originated from banana. Complete assemblies of the chromosomes confirmed their unique taxonomic position within clade 1 ofXanthomonas. Genome mining revealed novel genetic traits, hitherto undescribed in other members of theXanthomonasgenus. In strain CFBP 8444, we identified genes related to the synthesis of coronatine-like compounds, a phytotoxin produced by several pseudomonads, which raises interesting questions about the evolution and pathogenicity of this pathogen. In addition, strain CFBP 8444 was found to encode a second, atypical flagellar gene cluster in addition to the canonical flagellar gene cluster. Overall, this research represents an important step toward better understanding the evolutionary history and biology of early-branching xanthomonads.