XbmR, a new transcription factor involved in the regulation of chemotaxis, biofilm formation and virulence in Xanthomonas citri subsp. citri

Abstract

Xanthomonas citri subsp. citri (Xcc) is the causal agent of citrus canker. Biofilm formation on citrus leaves plays an important role in epiphytic survival of Xcc. Biofilm formation is affected by transposon insertion in XAC3733, which encodes a transcriptional activator of the NtrC family, not linked to a gene encoding a sensor protein, thus could be considered as an 'orphan' regulator whose function is poorly understood in Xanthomonas spp. Here we show that mutation of XAC3733 (named xbmR) resulted in impaired structural development of the Xcc biofilm, loss of chemotaxis and reduced virulence in grapefruit plants. All defective phenotypes were restored to wild-type levels by the introduction of PA2567 from Pseudomonas aeruginosa, which encodes a phosphodiesterase active in the degradation of cyclic diguanosine monophosphate (c-di-GMP). A knockout of xbmR led to a substantial downregulation of fliA that encodes a σ(28) transcription factor, as well as fliC and XAC0350 which are potential member of the σ(28) regulon. XAC0350 encodes an HD-GYP domain c-di-GMP phosphodiesterase. These findings suggest that XbmR is a key regulator of flagellar-dependent motility and chemotaxis exerting its action through a regulatory pathway that involves FliA and c-di-GMP.

Using Ecology, Physiology, and Genomics to Understand Host Specificity in Xanthomonas

“…In Xcci, chemotaxis toward host grapefruit leaf extracts was evidenced. This phenotype results from several mechanisms, including the regulation of flagellar motility by XbmR through a regulatory pathway that involves FliA and c-di-GMP (149). Recently, the MCP gene XCC0324 was found distributed in only one clade within the Xanthomonas genus.…”

Response regulator VemR regulates the transcription of flagellar rod gene flgG by interacting with σ54 factor RpoN2 in Xanthomonas citri ssp. citri

“…Flagellar motility governs the translational movement towards favourable environments in response to physical or chemical attractants (Ottamann and Miller, ). Moreover, flagellar‐dependent cell motility is essential for the establishment of a mature biofilm, and is thus involved in the ability to attach to host surfaces and to elicit canker lesions on citrus (Li and Wang, ; Malamud et al ., ; Viducic et al ., ; Yaryura et al ., ). In addition, the filament flagellin has been shown to be a pathogen‐associated molecular pattern, inducing innate immune responses in host plants (Zipfel et al ., ).…”

Lysobacter PilR, the Regulator of Type IV Pilus Synthesis, Controls Antifungal Antibiotic Production via a Cyclic di-GMP Pathway

“…Because several PilR-type transcription regulators, e.g., FleQ from P. aeruginosa (29,30) and XbmR from Xanthomonas citri (31), have been shown to bind c-di-GMP directly, (25). ΔpilR(pURF047), the ΔpilR mutant containing an empty vector; ΔpilR(pilR-cp2), the ΔpilR mutant with plasmid pilR-pUFR047, containing the intact pilR gene.…”