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A LOV protein modulates the physiological attributes of Xanthomonas axonopodis pv. citri relevant for host plant colonization.

Kraiselburd I, Alet AI, Tondo ML, Petrocelli S, Daurelio LD, Monzón J, Ruiz OA, Losi A, Orellano EG - PLoS ONE (2012)

Bottom Line: We also constructed a mutant strain of X. axonopodis pv. citri lacking the LOV protein and found that the loss of this protein altered bacterial motility, exopolysaccharide production and biofilm formation.Moreover, we observed that the adhesion of the mutant strain to abiotic and biotic surfaces was significantly diminished compared to the wild-type.Finally, inoculation of orange (Citrus sinensis) leaves with the mutant strain of X. axonopodis pv. citri resulted in marked differences in the development of symptoms in plant tissues relative to the wild-type, suggesting a role for the Xac-LOV protein in the pathogenic process.

View Article: PubMed Central - PubMed

Affiliation: Molecular Biology Division, Instituto de Biología Molecular y Celular de Rosario, CONICET, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Argentina.

ABSTRACT
Recent studies have demonstrated that an appropriate light environment is required for the establishment of efficient vegetal resistance responses in several plant-pathogen interactions. The photoreceptors implicated in such responses are mainly those belonging to the phytochrome family. Data obtained from bacterial genome sequences revealed the presence of photosensory proteins of the BLUF (Blue Light sensing Using FAD), LOV (Light, Oxygen, Voltage) and phytochrome families with no known functions. Xanthomonas axonopodis pv. citri is a Gram-negative bacterium responsible for citrus canker. The in silico analysis of the X. axonopodis pv. citri genome sequence revealed the presence of a gene encoding a putative LOV photoreceptor, in addition to two genes encoding BLUF proteins. This suggests that blue light sensing could play a role in X. axonopodis pv. citri physiology. We obtained the recombinant Xac-LOV protein by expression in Escherichia coli and performed a spectroscopic analysis of the purified protein, which demonstrated that it has a canonical LOV photochemistry. We also constructed a mutant strain of X. axonopodis pv. citri lacking the LOV protein and found that the loss of this protein altered bacterial motility, exopolysaccharide production and biofilm formation. Moreover, we observed that the adhesion of the mutant strain to abiotic and biotic surfaces was significantly diminished compared to the wild-type. Finally, inoculation of orange (Citrus sinensis) leaves with the mutant strain of X. axonopodis pv. citri resulted in marked differences in the development of symptoms in plant tissues relative to the wild-type, suggesting a role for the Xac-LOV protein in the pathogenic process. Altogether, these results suggest the novel involvement of a photosensory system in the regulation of physiological attributes of a phytopathogenic bacterium. A functional blue light receptor in Xanthomonas spp. has been described for the first time, showing an important role in virulence during citrus canker disease.

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Twitching-like motility of X. axonopodis pv. citri strains.X. axonopodis pv. citri WT, Δlov and Δlov-plov strains were stab-inoculated on SB-1% w/v agar plates and grown for two days at 28°C. To analyze the borders of the migration zones, the plates were observed under a magnifying glass (10X), prior (upper panels) and after (lower panels) staining with Coomassie Brilliant Blue R250.
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pone-0038226-g004: Twitching-like motility of X. axonopodis pv. citri strains.X. axonopodis pv. citri WT, Δlov and Δlov-plov strains were stab-inoculated on SB-1% w/v agar plates and grown for two days at 28°C. To analyze the borders of the migration zones, the plates were observed under a magnifying glass (10X), prior (upper panels) and after (lower panels) staining with Coomassie Brilliant Blue R250.

Mentions: Twitching motility is a type of bacterial translocation over moist surfaces mediated by the extension, attachment and retraction of type IV pili, previously described for several pathogenic bacteria [40], [41]. In order to evaluate the possibility of such migration mechanism we assayed the X. axonopodis pv. citri behavior in conditions known to favor twitching motility [40]. When we analyzed the bacterial migration zones obtained two days after stab-inoculating X. axonopodis pv. citri WT, Δlov and Δlov-plov strains onto SB-1% w/v agar plates, we observed that WT and Δlov-plov colonies showed an irregular appearance with long bacterial extensions irradiating from the migration zones, which resemble the bacterial rafts showed by some twitching-performing bacteria (Figure 4) [41]. Conversely, the Δlov strain developed smooth-margined colonies, with no visible bacterial extensions radiating from the central bacterial colony. Similar results were obtained when bacteria were grown in the darkness (detailed on Supporting Information S1 and Figure S5).


A LOV protein modulates the physiological attributes of Xanthomonas axonopodis pv. citri relevant for host plant colonization.

Kraiselburd I, Alet AI, Tondo ML, Petrocelli S, Daurelio LD, Monzón J, Ruiz OA, Losi A, Orellano EG - PLoS ONE (2012)

Twitching-like motility of X. axonopodis pv. citri strains.X. axonopodis pv. citri WT, Δlov and Δlov-plov strains were stab-inoculated on SB-1% w/v agar plates and grown for two days at 28°C. To analyze the borders of the migration zones, the plates were observed under a magnifying glass (10X), prior (upper panels) and after (lower panels) staining with Coomassie Brilliant Blue R250.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3366940&req=5

pone-0038226-g004: Twitching-like motility of X. axonopodis pv. citri strains.X. axonopodis pv. citri WT, Δlov and Δlov-plov strains were stab-inoculated on SB-1% w/v agar plates and grown for two days at 28°C. To analyze the borders of the migration zones, the plates were observed under a magnifying glass (10X), prior (upper panels) and after (lower panels) staining with Coomassie Brilliant Blue R250.
Mentions: Twitching motility is a type of bacterial translocation over moist surfaces mediated by the extension, attachment and retraction of type IV pili, previously described for several pathogenic bacteria [40], [41]. In order to evaluate the possibility of such migration mechanism we assayed the X. axonopodis pv. citri behavior in conditions known to favor twitching motility [40]. When we analyzed the bacterial migration zones obtained two days after stab-inoculating X. axonopodis pv. citri WT, Δlov and Δlov-plov strains onto SB-1% w/v agar plates, we observed that WT and Δlov-plov colonies showed an irregular appearance with long bacterial extensions irradiating from the migration zones, which resemble the bacterial rafts showed by some twitching-performing bacteria (Figure 4) [41]. Conversely, the Δlov strain developed smooth-margined colonies, with no visible bacterial extensions radiating from the central bacterial colony. Similar results were obtained when bacteria were grown in the darkness (detailed on Supporting Information S1 and Figure S5).

Bottom Line: We also constructed a mutant strain of X. axonopodis pv. citri lacking the LOV protein and found that the loss of this protein altered bacterial motility, exopolysaccharide production and biofilm formation.Moreover, we observed that the adhesion of the mutant strain to abiotic and biotic surfaces was significantly diminished compared to the wild-type.Finally, inoculation of orange (Citrus sinensis) leaves with the mutant strain of X. axonopodis pv. citri resulted in marked differences in the development of symptoms in plant tissues relative to the wild-type, suggesting a role for the Xac-LOV protein in the pathogenic process.

View Article: PubMed Central - PubMed

Affiliation: Molecular Biology Division, Instituto de Biología Molecular y Celular de Rosario, CONICET, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Argentina.

ABSTRACT
Recent studies have demonstrated that an appropriate light environment is required for the establishment of efficient vegetal resistance responses in several plant-pathogen interactions. The photoreceptors implicated in such responses are mainly those belonging to the phytochrome family. Data obtained from bacterial genome sequences revealed the presence of photosensory proteins of the BLUF (Blue Light sensing Using FAD), LOV (Light, Oxygen, Voltage) and phytochrome families with no known functions. Xanthomonas axonopodis pv. citri is a Gram-negative bacterium responsible for citrus canker. The in silico analysis of the X. axonopodis pv. citri genome sequence revealed the presence of a gene encoding a putative LOV photoreceptor, in addition to two genes encoding BLUF proteins. This suggests that blue light sensing could play a role in X. axonopodis pv. citri physiology. We obtained the recombinant Xac-LOV protein by expression in Escherichia coli and performed a spectroscopic analysis of the purified protein, which demonstrated that it has a canonical LOV photochemistry. We also constructed a mutant strain of X. axonopodis pv. citri lacking the LOV protein and found that the loss of this protein altered bacterial motility, exopolysaccharide production and biofilm formation. Moreover, we observed that the adhesion of the mutant strain to abiotic and biotic surfaces was significantly diminished compared to the wild-type. Finally, inoculation of orange (Citrus sinensis) leaves with the mutant strain of X. axonopodis pv. citri resulted in marked differences in the development of symptoms in plant tissues relative to the wild-type, suggesting a role for the Xac-LOV protein in the pathogenic process. Altogether, these results suggest the novel involvement of a photosensory system in the regulation of physiological attributes of a phytopathogenic bacterium. A functional blue light receptor in Xanthomonas spp. has been described for the first time, showing an important role in virulence during citrus canker disease.

Show MeSH
Related in: MedlinePlus