title: Bacteria causing important diseases of citrus utilise distinct modes of pathogenesis to attack a common host.
abstract: In this review, we summarise 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. Xylella fastidiosa and Candidatus Liberibacter are vectored by insects and proliferate in the vascular system of the host, either in the phloem (Candidatus Liberibacter) or xylem (X. fastidiosa) causing variegated chlorosis and huanglongbing diseases, respectively. Candidatus 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 amongst 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.
authors.affiliation: Instituto de Ciencia y Tecnología Dr. Cesar Milstein, Fundación Pablo Cassará, Consejo Nacional de Investigaciones Científicas y técnicas (CONICET), Saladillo 2468, C1440FFX, Buenos Aires, Argentina. avojnov@fundacioncassara.org.ar
authors.forename: Adrián Alberto
authors.initials: AA
authors.lastname: Vojnov
authors.forename: Alexandre Morais
authors.initials: AM
authors.lastname: do Amaral
authors.forename: John Maxwell
authors.initials: JM
authors.lastname: Dow
authors.forename: Atilio Pedro
authors.initials: AP
authors.lastname: Castagnaro
authors.forename: Marìa Rosa
authors.initials: MR
authors.lastname: Marano
mesh_terms: D001419:Bacteria / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002957:Citrus / Q000382:microbiology*; D054884:Host-Pathogen Interactions; D010935:Plant Diseases / Q000382:microbiology*; D014774:Virulence
chemical_list: D001426:Bacterial Proteins