Biosynthesis of Coenzyme Q in the Phytopathogen Xanthomonas campestris via a Yeast-Like Pathway

Coenzyme Q (CoQ) is a lipid-soluble membrane component found in organisms ranging from bacteria to mammals. The biosynthesis of CoQ has been intensively studied in Escherichia coli, where 12 genes (ubiA, -B, -C, -D, -E, -F, -G, -H, -I, -J, -K, and -X) are involved. In this study, we first investigated the putative genes for CoQ8 biosynthesis in the phytopathogen Xanthomonas campestris pv. campestris using a combination of bioinformatic, genetic, and biochemical methods. We showed that Xc_0489 (coq7 Xc ) encodes a di-iron carboxylate monooxygenase filling the E. coli UbiF role for hydroxylation at C-6 of the aromatic ring. Xc_0233 (ubiJ Xc ) encodes a novel protein with an E. coli UbiJ-like domain organization and is required for CoQ8 biosynthesis. The X. campestris pv. campestris decarboxylase gene remains unidentified. Further functional analysis showed that ubiB and ubiK homologs ubiB Xc and ubiK Xc are required for CoQ8 biosynthesis in X. campestris pv. campestris. Deletion of ubiJ Xc , ubiB Xc , and ubiK Xc led to the accumulation of an intermediate 3-octaprenyl-4-hydroxybenzoic acid. UbiK Xc interacts with UbiJ Xc and UbiB Xc to form a regulatory complex. Deletion analyses of these CoQ8 biosynthetic genes indicated that they are important for virulence in Chinese radish. These results suggest that the X. campestris pv. campestris CoQ8 biosynthetic reactions and regulatory mechanisms are divergent from those of E. coli. The variations provide an opportunity for the design of highly specific inhibitors for the prevention of infection by the phytopathogen X. campestris pv. campestris.