The causal agent of citrus canker is the bacteria Xanthomonas axonopodis pv. citri (Xac), which responds for important losses worldwide due to the damage caused in the production and quality of the fruits, and the absence of efficient control methods to this phytopathogen. The disease symptoms can be induced on leaves, stems and fruits of citrus host plants, and are characterized by localized host cell hyperplasia followed by tissue necrosis at the infected area. At the Xac post-genomic stage, we have been undertaking a proteomic approach to analyze differentially expressed proteins during Xac attack to citrus host plants. Total protein extracts were obtained from non-infecting Xac, grown on Nutrient medium; and infecting Xac, grown in three conditions: on XVMB inductive synthetic medium  (mimetizing Xac infection 1 day within host plant) and directly inoculated on host plant’s leafs and recovered 3 and 5 days after infection). The four protein extracts of Xac, obtained from both non-infecting and infecting conditions, were analyzed by two-dimensional electrophoresis and differentially expressed protein spots were digested with trypsin and the resulting peptides were analyzed on a MALDI TOF-TOF mass spectrometer. We identified about 600 spots for each condition. Taking non-infecting condition as reference we could identify up and down-regulated proteins as well as proteins detected at only one of each 1, 3 or 5 days after induction-infection condition. Among Xac proteins expressed under pathogen attack to the host it could be distinguished those responsible to neutralizing plant oxidative burst response against bacterial attack, virulence factors, type III secretion system proteins, plant cell wall degrading enzyme, iron receptor-transport proteins, and many hypothetical proteins. The possible role for these proteins to the fitness and virulence of Xac when in contact with citrus host are being argued.
Support: Auxílio Jovem Pesquisador FAPESP, CAPES and FUNDECITRUS