Differentially expressed proteins in the interaction of Xanthomonas axonopodis pv. citri with leaf extract of the host plant

The present study reports the expression of proteins of Xanthomonas axonopo dis pv. citri in response to different growth conditions. The bacterium was cultured in the basal medium MM1 and in the presence of leaf extracts from a susceptible host plant (sweet orange) as well as a resistant (ponkan) an d a nonhost plant (passion fruit). The protein profiles were analyzed by tw o-dimensional gel electrophoresis (2-DE). Twelve differential spots (induce d, up- and down-regulated and repressed) were observed in the protein profi les of the bacterium cultivated in citrus extract (susceptible host) when c ompared to that of MM1. The 2-DE profile of the bacterium cultured in the c omplex medium nutrient yeast glycerol was also obtained and the comparison with that of MM1 revealed 36 differential spots. Five proteins from the dif ferent treatments were successfully N-terminally sequenced and the putative functions were assigned by homology searches in databases. Two constitutiv ely expressed proteins, B4 and B5, were identified as pseudouridine synthas e and elongation factor P, respectively. The large subunit of ribulose 1,5- biphosphate carboxylase/oxygenase and a sulfate binding protein were found as specifically up-regulated in the presence of citrus extracts. Finally, t he heat shock protein G was found exclusively in the complex medium and rep ressed in all other media.