[show abstract][hide abstract] ABSTRACT: Xanthomonas citri spp. citri (Xcc)develops a biofilm structure both in vitro and in vivo. Despite all the progress achieved by studies regarding biofilm formation, many of its mechanisms remain poorly understood. This work focuses on the identification of new genes involved in biofilm formation and how they are related to motility, virulence and chemotaxis in Xcc. A Tn5 library of approximately 6,000 Xcc (strain 306) mutants was generated and screened to search for biofilm formation defective strains. We identified 23 genes whose association with the biofilm formation resulted in a novelty. The analysis of the 23 mutants revealed not only the involvement of new genes in biofilm formation but also reinforced the importance of exopolysaccharide production, motility and cell surface structures in this process. This collection of biofilm defective mutants underscores the multifactorial genetic program underlying the establishment of biofilm in Xcc.
[show abstract][hide abstract] ABSTRACT: In this study, we used real-time quantitative PCR (RT-qPCR) to evaluate the expression of 32 genes of Xanthomonas axonopodis pv. citri related to pathogenicity and virulence that are also involved in copper detoxification. Nearly all of the genes were up-regulated, including copA and copB. Two genes homologous to members of the type II secretion system (xcsH and xcsC) and two involved in the degradation of plant cell wall components (pglA and pel) were the most expressed in response to an elevated copper concentration. The type II secretion system (xcs operon) and a few homologues of proteins putatively secreted by this system showed enhanced expression when the bacteria were exposed to a high concentration of copper sulfate. The enhanced expression of the genes of secretion II system during copper stress suggests that this pathway may have an important role in the adaptative response of X. axonopodis pv. citri to toxic compounds. These findings highlight the potential role of these genes in attenuating the toxicity of certain metals and could represent an important means of bacterial resistance against chemicals used to control diseases.
Genetics and Molecular Biology 04/2010; 33(2):348-53. · 0.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Gram-negative bacterium Xanthomonas axonopodis pv. citri, the causal agent of citrus canker, is a major threat to the citrus industry worldwide. Although this is a leaf spot pathogen, it bears genes highly related to degradation of plant cell walls, which are typically found in plant pathogens that cause symptoms of tissue maceration. Little is known on Xac capacity to cause disease and hydrolyze cellulose. We investigated the contribution of various open reading frames on degradation of a cellulose compound by means of a global mutational assay to selectively screen for a defect in carboxymethyl cellulase (CMCase) secretion in X. axonopodis pv. citri. Screening on CMC agar revealed one mutant clone defective in extracellular glycanase activity, out of nearly 3,000 clones. The insertion was located in the xpsD gene, a component of the type II secretion system (T2SS) showing an influence in the ability of Xac to colonize tissues and hydrolyze cellulose. In summary, these data show for the first time, that X. axonopodis pv. citri is capable of hydrolyzing cellulose in a T2SS-dependent process. Furthermore, it was demonstrated that the ability to degrade cellulose contributes to the infection process as a whole.
Genetics and Molecular Biology 01/2010; 33(1):146-53. · 0.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: The progeny of 87 BC(1) hybrids of 'Murcott' tangor and 'Pera' sweet orange, genotyped with fluorescent amplified fragment length polymorphism (fAFLP) markers, was used for the construction of genetic maps for both citrus varieties. Mapping strategies, considering the progeny as a result of backcrossing and cross-pollination, were exploited in Mapmaker 2.0 (LOD score >or= 3.0 and <or= 0.40) and JoinMap 3.0 software (LOD score >or= 3.0 and theta <or = 0.25), respectively. Genetic map distances (in cM) between the linked fAFLPs were estimated, in both packages, by the Kosambi's function. Maps of both parents were constructed in Mapmaker with 121 of the 202 fAFLP markers showing 1:1 Mendelian segregation rates ('Murcott' map: 65 fAFLPs, average distance between them 29.5 cM, divided into 9 linkage groups (LGs), total size 1651.47 cM; 'Pera' map: 55 fAFLPs, average distance between them 31.9 cM, divided into 5 LGs, total size 1596.2 cM). The second 'Murcott' map, constructed through linkage analysis of 347 fAFLP markers with 3:1 or 1:1 segregation rates by using JoinMap, resulted in the linkage of 227 markers with an average distance of 4.25 cM among them, divided into 9 LGs of 845 cM. fAFLP loci showing distorted segregation and/or clustered were observed in different LGs of the maps generated by all the software. The use of the 'Murcott' tangor and 'Pera' sweet orange genetic maps in research on identification of citrus QRLs (quantitative resistance loci) to Xylella fastidiosa and QTLs (quantitative trait loci) related to the productivity and quality of the juice, respectively, is discussed.
Journal of applied genetics 01/2007; 48(3):219-31. · 1.85 Impact Factor