Effects of Mutations in the Xanthomonas axonopodis pv. citri Lipopolysaccharide on Citrus Canker

PETROCELLI, S.; CASABUONO, A.C.; COUTO, A.; OTTADO, J.; ORELLANO, E.G.

Carlos Paz, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2008

SAIB

A broad range of pathogens is recognized by plants through so-called pathogen-associated molecular patterns (PAMPs), which are highly conserved fragments of pathogenic molecules. In plant pathogenic bacteria, lipopolisaccharyde (LPS) is an important virulence factor and it is being recognized as a PAMP. Stomatal closure is part of a plant innate immune response. Citrus canker is produced by Xanthomonas axonopodis pv. citri (Xac). The aim of this study is to determine the effect of Xac mutant strains defective in genes (wzt and rfb303) involved in LPS biosynthesis on citrus canker. The structures of LPS from Xac-wzt and Xac-rfb303 were determined and differences between LPS from Xac and mutants strains were observed. Incubation of orange leaves with LPS isolated of Xac wild-type (wt), Xac-wzt and Xac-rfb303 induced stomatal closure after 2 hours. On the other hand, incubation of orange leaves with bacteria induced stomatal aperture after 3 hours. It is established that bacterial LPS can induce accumulations of transcripts of a number of defense-related genes like PR, PrxA, GST and MAPKs in plants. Expression changes in genes that are involved in basal defense were observed in orange leaves infected with Xac wt, Xac-wzt and Xac-rfb303 at 6 and 24 hours post-infiltration. These results suggest that LPS of Xac acts as a PAMP in Xac-orange interaction.