CONICET | Buscador de Institutos y Recursos Humanos

In this review, we summarize the current knowledge on three pathogens that exhibit distinct tissue specificity and modes of pathogenesis in citrus plants. Xanthomonas axonopodis pv. citri causes canker disease and invades the host leaf mesophyll tissue through natural openings and can also survive as an epiphyte. X. fastidiosa and Ca. Liberibacter are vectored by insects and proliferate in the vascular system of the host, either in the phloem (Ca. Liberibacter) or xylem (X. fastidiosa) causing variegated chlorosis and huanglongbing diseases, respectively. Ca. Liberibacter can be found within host cells and is thus unique as an intracellular phytopathogenic bacterium. Genome sequence comparisons have identified groups of species-specific genes that may be associated with the particular lifestyle, mode of transmission or symptoms produced by each phytopathogen. In addition, components that are conserved among bacteria may have diverse regulatory actions underpinning the different bacterial lifestyles; one example is the divergent role of the Rpf/DSF cell-cell signalling system in X. citri and X.fastidiosa. Biofilm plays a key role in epiphytic fitness and canker development in X. citri and in the symptoms produced by X. fastidiosa. Bacterial aggregation may be associated with vascular occlusion of the xylem vessels and symptomatology of variegated chlorosis.