A LOV Protein Modulates the Physiological Attributes of Xanthomonas axonopodis pv. citri Relevant for Host Plant Colonization

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.

Using Ecology, Physiology, and Genomics to Understand Host Specificity inXanthomonas

“…Bacteria have evolved a repertoire of sensory proteins that may detect environmental signals such as bacterial cell density or the presence of chemoattractants or chemorepellents, oxygen, and light (80,90). The total number of sensory and signaling proteins encoded by a bacterial genome was proposed as a measure of the adaptive potential of the bacterium, i.e., its intelligence quotient (IQ) (49).…”

Light Regulation of Swarming Motility in Pseudomonas syringae Integrates Signaling Pathways Mediated by a Bacteriophytochrome and a LOV Protein

“…Following autophosphorylation, the P. syringae LOV-HK protein rapidly transferred the phosphate to this RR domain, at least when the domains were cloned separately (30). This domain structure is found primarily in bacterial plant pathogens (31). …”

Identification and characterization of biofilm formation-defective mutants of Xanthomonas citri subsp. citri

“…On: Thu, 04 Apr 2019 13:22:49 glucan biosynthesis (Malamud et al, 2012), a twocomponent signal transduction system encoded by colS/ colR (Yan & Wang, 2011) and a LOV protein (Kraiselburd et al, 2012) are the elements found to be a requirement for Xcc biofilm.…”