Role of xanthan gum in the interaction of Xanthomnas axonopodis pv. citri and Citrus limon.

SICILIANO F.; ENRIQUE R.; RIGANO L.; BERMEJO C.; CASTAGNARO A.; VOJNOV A.; MARANO M.R.

Rosario

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB); 2006

SAIB

The phytopathogenic bacterium Xanthomonas axonopodis pv. citri (Xac) is responsible for the canker disease affecting citrus plants throughout the world. Previously, we had shown that Xac biofilm structure was dramatically influenced by xanthan production in vitro. In this work, we demonstrated that xanthan is essential for bacterial attachment, epiphytic growth and survival on lemon leaves. We used confocal laser scanning microscopy to analyze lemon leaves infected with GFP-labeled Xac cells in order to test how closely biofilm formation on abiotic surfaces mimics pathogen-induced canker development in citrus plants. As we observed in the in vitro experiments, the xanthan-deficient mutant (MgumB) grows as single cells and does not induce microcolonies on lemon leaves during the length of experiment, indicating that xanthan affects aggregate formation. Coinoculation of wild-type Xanthomonas campestris pv. campestris (Xcc) and the Xac gum mutant onto lemon leaves reverted the canker phenotype, confirming the role of the EPS in canker development. We analyzed the biochemical and molecular changes triggered by Xac and Xac MgumB in Citrus limon plants, such as deposition of callose and expression of pathogenicity related genes (PR-1a). Our preliminary results suggest that xanthan are able to suppress, in earliest stages of infection, the defense response in lemon leaves.