A gene for a dioxygenase‐like protein determines the production of the DF signal in Xanthomonas campestris pv. campestris

Abstract

SUMMARY The DF signal molecule regulates the production of both yellow pigments (xanthomonadins) and extracellular polysaccharide (EPS) in Xanthomonas campestris pv. campestris. These two bacterial products are crucial to the epiphytic survival and pathogenicity of this pathogen on its plant hosts. Previous work suggested that DF is a butyrolactone, which the Streptomyces bacteria are known to utilize as signals. pigB is one of seven transcriptional units in the X. c. pv. campestris xanthomonadin gene cluster, and its inactivation results in the loss of DF signal, xanthomonadin and EPS production. Here, determination and analysis of the pigB DNA sequence reveals the presence of two open reading frames, the first (xanB1) encoding a putative reductase/halogenase, and the second (xanB2) showing the highest level of identity to Streptomyces genes encoding putative pteridine-dependent dioxygenase-like proteins. We show that xanB2 (but not xanB1) is needed for production of the DF signal, and that some Streptomyces strains produce functional analogues of DF. A role for xanB2 in the biosynthesis of DF is proposed.

Biosynthesis of the immunosuppressants FK506, FK520, and rapamycin involves a previously undescribed family of enzymes acting on chorismate

“…A block in aroE in the early part of the shikimate pathway abolishes xanthomonadin biosynthesis (46). Deletion of the gene for the FkbO/RapK-like protein abolishes both pigment production and extracellular polysaccharide production dependent on a diffusible factor (47). Because these authors had relied on early annotation of FkbO/RapK-like proteins as pteridine-dependent dioxygenases, the recognition of these proteins as potential 3HBA synthases should lead to a useful reevaluation of their role in Xanthomonas and related phytopathogenic bacteria (48).…”

Diffusible signals and interspecies communication in bacteria

“…Xcc synthesizes a second signal molecule called DF, which has a partially overlapping regulatory function with DSF (Chun et al, 1997;Poplawsky et al, , 2005. The DF signal molecule in Xcc strain B-24 regulates the production of both yellow pigments (xanthomonadins) and extracellular polysaccharide (EPS) and is critical for epiphytic colonization and infection of the host plant .…”

“…Butyrolactone signal molecules have been studied extensively in Streptomyces spp., where they control morphological differentiation and secondary metabolite production via quorum sensing (Horinouchi, 1999;Chater & Horinouchi, 2003), and recently the first gene for the biosynthesis of a Streptomyces butyrolactone signal was cloned (Shikura et al, 2002;Kato et al, 2007). Several Streptomyces strains are able to restore production of xanthomonadin and extracellular polysaccharide when streaked adjacent to an Xcc xanB2 mutant (Poplawsky et al, 2005). Determination of the structure of DF and elucidation of the mechanism(s) of DF perception should build upon these intriguing observations and help to establish whether a common strategy for the use and perception of butyrolactones as signalling molecules exists in Xanthomonas and Streptomyces.…”

“…The DF signal molecule in Xcc strain B-24 regulates the production of both yellow pigments (xanthomonadins) and extracellular polysaccharide (EPS) and is critical for epiphytic colonization and infection of the host plant . Synthesis of DF depends upon the pigB locus and specifically xanB2 (XCC4014), whose predicted amino acid sequence shows moderate similarity to putative pteridine-dependent dioxygenases from Streptomyces spp., but no homology to known regulatory genes (Poplawsky et al, 2005). DF has been tentatively identified by mass spectrometry as a butyrolactone (Chun et al, 1997).…”

Synthesis of Microbial Signaling Molecules and Their Stereochemistry-Activity Relationships

“…That is, AHLs from several other bacterial genera did not restore pigment or EPS production in the pigB mutant strains, 66,71) and several Streptomyces strains which produce butyrolactones such as A-factor (52) restored both these traits in pigB mutant strains. 72) These results indicate that DF of Xcc might be a molecule related to A-factor. Hence it is strongly recommended that the structure of DF of Xcc be reinvestigated.…”