CaracterizaÃÃo da variabilidade natural da resposta a um isolado brasileiro de Xanthomonas campestris pv. campestris em Arabidopsis thaliana

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Phytopathogens are problems for agriculture as they reduce both crop quality and quantity. Chemicals are frequently used to control plant pathogens. However, they are undesirable because of increased production costs to farmers as well as environmental and consumer health negative impacts. An alternative to the use of chemicals is the development of varieties of plants with genetic resistance against pathogens. Arabidopsis thaliana has been used as a model system to study the genetic factors involved in the plant-pathogen-host interaction. This work aimed to study the interaction between A. thaliana and Xanthomonas campestris pv. campestris, an important pathogen of crucifers responsible for a disease named Black-rot. Initially, the response of thirty - three ecotypes of A. thaliana against the isolate Xcc CNPH 17. Although immunity was not observed, ecotypes CS 1308, CS 1566 and CS 1643 grown in continuous light showed resistance when inoculated with a bacterium suspension of 5 x 106 CFU/mL. In contrast, ecotypes CS 1194 and CS 1492 were found to be more susceptible showing strong symptoms of chlorosis. Similar results were obtained when plants were grown under short days. In order to quantify differences on the degree of disease symptoms, total chlorophyll was extracted from contrasting ecotypes at different time points after inoculation. Chlorophyll levels from controls and inoculated plants had similar reduction among resistant ecotypes. In susceptible ecotypes inoculated plants showed a more pronounced reduction in inoculated plants than in controls. In order to test how broad was the identified resistance in ecotypes CS 1308, CS 1566, CS 1643 and CS 1438 (that showed intermediate resistance to CNPH 17), these ecotypes were inoculated with the isolate CNPH 77 of Xcc. All ecotypes developed disease symptoms, however ecotype CS 1566 showed some level of resistant to this aggressive isolate of Xcc. The resistant ecotypes CS 1308, CS 1566 and CS 1643 to isolate Xcc CNPH 17 were also inoculated with Ralstonia solanacearum (Rs CNPH 221), an important soil pathogen of solaneracea crops. The ecoptype CS 1308 was more resistant than ecotypes CS 1566 and CS 1643, which showed an intermediate resistance level. In order to begin characterizing the mechanism of resistance, ecotypes CS 1308, CS 1566 and CS 1643, were inoculated with a high titer of Xcc CNPH 17 (5 x 108 CFU/mL) and symptom development was monitored at 7, 24 and 48 h after inoculation. No symptoms of hypersensitive response were observed. To perform in planta studies of bacterial growth it is important to be able to assess the bacterial population without the presence of spurious contaminants which can be achieved by adding antibiotics to media. Thus, the resistance/sensitivity of Xcc CNPH 17 to different antibiotics was investigated. This isolate showed sensitivity to chloramphenicol, kanamycin, spectiomycin, estreptomycin, tetracycline and rifampicin in concentrations tested. Given these results, a spontaneous rifampicin mutant was sought after. Mutants resistant to 25 mg/mL of rifampicin were obtained. These mutants will be used fot growth cure experiments and should be helpful in unraveling the mechanism of disease resistance to Xcc CNPH 17

ASSUNTO(S)

xanthomonas campestris pv. campestris patÃgeno host variabilidade natural pathosystem biofisica molecular hospedeiro arabidopsis thaliana pathogen natural variability arabidopsis thaliana patossistema

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