A two component regulator BfdR regulates biofilm formation and virulence through the rpf/DSF system in Xanthomonas axonopodis pv. citri

• Main Authors: Yu-Hsuan Chen, 陳郁璇
• Other Authors: Tzu-Pi Huang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/11453918127482666794

碩士 === 國立中興大學 === 植物病理學系所 === 101 === Citrus bacteria canker, which is caused by Xanthomonas axonopodis pv. citri (syn. X. citri subsp. citri) is the most devastating bacterial disease of citrus plants worldwide. In our previous study, to understand the mechanisms of biofilm formation by X. axonopodis pv. citri, strain XW19 was subjected for transposon mutagenesis and biofilm formation defective mutants for further analysis. The mutant with a mutation of two-component response regulator gene bfdR (for biofilm formation defective, regulator) which showed reduction in the development of biofilm on the leaf surfaces of citrus plants and canker lesions as well as epiphytic growth was isolated. BfdR was also found to positively control the rpfF gene expression in XVM2 medium, the medium which mimics the cytoplasmic fluid in plants. The results indicated that biofilm formation and bacterial survival of X. axonopodis pv. citri on leaf surfaces of citrus are associated with bacterial virulence and is controlled by BfdR through regulation of rpfF. Here, we investigate whether X. axonopodis pv. citri BfdR controls biofilm formation via rpf/DSF system and its regulatory mechanisms. The transcript levels of genes in the rpf (for regulation of pathogenicity factors) gene cluster and carAB in the wild type, bfdR mutant and the complemented strain were assessed. The results from semi-quantitative reverse-transcription polymerase chain reaction showed that the transcript levels of rpfB, rpfF and carA were reduced ; while those of rpfA, rpfC, rpfD and rpfG were regulated in the bfdR mutant compared to the wild type and the complemented strain. The transcript levels of carB in all three strains were similar. The extracellular fatty acids of X. axonopodis pv. citri XW19 harboring rpfF in trans, strain YHC1, were analyzed using reverse-phase high-performance liquid chromatography. A peak at retention time 10-11 mins and UV absorption at 210 nm was found in samples from strain YHC1 similar to the synthetic cis-11-methyl-2-dodecenoic acid. The data suggested that the products synthesized by rpfF of X. axonopodis pv. citri XW19 may be close derivatives of cis-11-methyl-2- dodecenoic acid. In conclusion, our results suggested that BfdR of X. axonopodis pv. citri strain XW19 controls biofilm formation through regulation of gene expression in rpf/DSF system. Addition of synthetic DSF in the tryptic soy broth restored biofilm formation by the bfdR mutant on polystyrene and leaf surfaces of citrus that by the wild type.