A Filamentous Hemagglutinin-Like Protein of Xanthomonas axonopodis pv. citri, the Phytopathogen Responsible for Citrus Canker, Is Involved in Bacterial Virulence

Abstract

Xanthomonas axonopodis pv. citri, the phytopathogen responsible for citrus canker has a number of protein secretion systems and among them, at least one type V protein secretion system belonging to the two-partner secretion pathway. This system is mainly associated to the translocation of large proteins such as adhesins to the outer membrane of several pathogens. Xanthomonas axonopodis pv. citri possess a filamentous hemagglutinin-like protein in close vicinity to its putative transporter protein, XacFhaB and XacFhaC, respectively. Expression analysis indicated that XacFhaB was induced in planta during plant-pathogen interaction. By mutation analysis of XacFhaB and XacFhaC genes we determined that XacFhaB is involved in virulence both in epiphytic and wound inoculations, displaying more dispersed and fewer canker lesions. Unexpectedly, the XacFhaC mutant in the transporter protein produced an intermediate virulence phenotype resembling wild type infection, suggesting that XacFhaB could be secreted by another partner different from XacFhaC. Moreover, XacFhaB mutants showed a general lack of adhesion and were affected in leaf surface attachment and biofilm formation. In agreement with the in planta phenotype, adhesin lacking cells moved faster in swarming plates. Since no hyperflagellation phenotype was observed in this bacteria, the faster movement may be attributed to the lack of cell-to-cell aggregation. Moreover, XacFhaB mutants secreted more exopolysaccharide that in turn may facilitate its motility. Our results suggest that this hemagglutinin-like protein is required for tissue colonization being mainly involved in surface attachment and biofilm formation, and that plant tissue attachment and cell-to-cell aggregation are dependent on the coordinated action of adhesin molecules and exopolysaccharides.

The ColR/ColS Two-Component System Plays Multiple Roles in the Pathogenicity of the Citrus Canker Pathogen Xanthomonas citri subsp. citri

“…The average of four replicates was used for quantitative measurement. Assays of biofilm formation on leaf surfaces were conducted as described previously (13). Briefly, 20 l of each bacterial suspension (10 8 CFU ml…”

Functional roles of the pepper leucine-rich repeat protein and its interactions with pathogenesis-related and hypersensitive-induced proteins in plant cell death and immunity

“…Fha proteins of plant pathogens such as Erwinia chrysanthemi, Xanthomonas axonopodis pv. citri, and Xylella fastidiosa function as virulence factors by modulating surface attachment, biofilm formation, and cell-to-cell aggregation during host plant infection (Rojas et al 2002;Guilhabert and Kirkpatrick 2005;Gottig et al 2009). Pepper cell death is triggered in leaf tissues by Xcv-releasing Fha1 (Choi et al 2013).…”

Bacterial Citrus Diseases: Major Threats and Recent Progress

“…The genomes of Xfa and Xcc contain genes coding for adhesins predicted to be secreted by mechanisms resembling type V secretion systems (T5SS). Adhesins are high molecular weight proteins that play key roles in adhesion and biofilm formation [54,96]. Genes coding for adhesins are upregulated in Xfa biofilms in vitro [94].…”