Resumo

Chromosome segregation is an essential process to all living cells. In prokaryotes, it is part of an interlinked sequence of events known as the cell cycle, which could be didactically divided into chromosome replication, segregation, cell division, and cellular growth. The factors that operate on each of these processes have been extensively characterized in eukaryotes, and among the techniques employed, fluorescence microscopy has surely contributed in a singular manner for the advancement in the comprehension of eukaryotic mitosis. Although the same degree of understanding has not been achieved yet for the prokaryotic cells, in the past decade, a collection of reports have clarified that bacteria too have a mitotic-like apparatus that resembles the eukaryotic one. Here, we report on the characterization of the ParB-like protein encoded by the plant pathogen Xanthomonas citri (Xac). In many bacteria, ParB organizes a centromere structure upon DNA-binding, which operates on chromosome segregation, it may contact other cellular factors that modulate its function, and disruption/knockout of ParB exhibited pleiotropic effects in some microorganisms such as loss of motility and loss of control on cell division. ParB-GFP expressed in Xanthomonas citri localized at the edges of the nucleoids, a phenotype typical of ParB-like factors involved with chromosome segregation. Moreover, disruption of parB in Xac led to loss of virulence, where Xac parB mutants were unable to induce citrus canker symptoms in host citrus plants. Finally, perturbation of the ParB function in Xac produced cells with a propensity to form filaments, a phenotype suggestive of a loss of control on cell division. ParB-like proteins have no homologues on eukaryotic cells, hence, they can be considered as potential targets for the development of antimicrobial agents. Our data supports this view in which Xac cells expressing altered forms of ParB were not able to cause disease on citrus plants. Financial support: FAPESP Grant 2010/05099-7, AMU PhD scholarship 2010/02041-8, and CNPq PMMM PhD scholarship 142293/2009-1