A filamentous hemagglutinin-like protein of Xanthomonas axonopodis pv. citri, the phytopathogen responsible for citrus canker, is involved in bacterial virulence

ZIMARO T; GARAVAGLIA BS; GAROFALO CG; ORELLANO EG; OTTADO J; GOTTIG N

La Plata, Argentina

Congreso; XVIII Reunión Argentina de Fisiología Vegetal; 2010

Sociedad Argentina de Fisiología Vegetal

Citrus canker, caused by Xanthomonas axonopodis pv. citri (Xac), is one of the most devastating diseases affecting citrus production worldwide. The pathogen enters host plant tissues through stomatal openings or wounds and then colonizes the apoplast, but little is known about the mechanisms that mediate Xac adhesion to host surface. In Bordetella pertussis an animal pathogen, the non-fimbrial adhesin FhaB is secreted in a Sec-dependent manner by the two-partner secretion system, which involves an outer membrane-associated accessory protein (FhaC partner protein). We studied the role of FhaB and FhaC homologs in Xac (XacFhaB and XacFhaC respectively). Our results indicate that XacFhaB is involved in Xac pathogenicity, particularly mediating pathogen attachment to the leaf surface and also in bacterial biofilm formation. Moreover, XacFhaB contributes to Xac motility since the in absence of this adhesin Xac has less cell-to-cell contact and also produces more exopolysaccharide that helps in bacteria swarming. Indeed, in the absence of this adhesion Xac produces less and more dispersed canker lesions compared to the wild type bacteria. Our results show that non-fimbrial adhesins are important factors that contribute to phytopathogenic host colonization and virulence. We are currently studying which regions of the XacFhaB molecule are implicated in the adherence mechanisms. Our new results suggest that a domain that we called carbohydrate binding domain based on the homology of this domain with Bordetella FhaB is mediating Xac cell-to cell attachment by interacting with Xac exopolysaccharide xanthan.