RESUMO
sRNA-Xcc1 is a trans-acting sRNA recently identified from the plant pathogenic bacterium Xanthomonas campestris pathovar campestris (Xcc). Here, the phylogenetic distribution, predicted secondary structure and regulation of expression of sRNA-Xcc1 were analyzed. The analysis showed (1) a total 81 sRNA-Xcc1 homologs that are found in some bacterial strains that are taxonomically unrelated, belonging to the α-, ß-, γ- and δ-proteobacteria (2) that some sRNA-Xcc1 homologs are located in a plasmid-borne transposon or near a transposase coding gene, (3) that sRNA-Xcc1 is encoded by a integron gene cassette in Xcc and sRNA-Xcc1 homologs occur in integron gene cassettes of some uncultured bacteria and (4) that sRNA-Xcc1 homologs have a highly conserved sequence motif and a stable consensus secondary structure. These findings strongly support the idea that sRNA-Xcc1 represents a novel family of sRNAs which may be originally captured by integrons from natural environments and then spread among different bacterial species via horizontal gene transfer, possibly by means of transposons and plasmids. The expression analysis results demonstrated that the transcription of sRNA-Xcc1 is under the positive control of the key virulence regulators HrpG and HrpX, indicating that sRNA-Xcc1 may be involved in the virulence regulation of Xcc.
Assuntos
Proteínas de Bactérias/genética , RNA Bacteriano/genética , Pequeno RNA não Traduzido/genética , Transativadores/genética , Fatores de Transcrição/genética , Xanthomonas campestris/genética , Sequência de Bases , Northern Blotting , Elementos de DNA Transponíveis/genética , Regulação Bacteriana da Expressão Gênica , Integrons/genética , Dados de Sequência Molecular , Mutação , Conformação de Ácido Nucleico , Filogenia , Plasmídeos/genética , Regiões Promotoras Genéticas/genética , RNA Bacteriano/química , RNA Bacteriano/classificação , Pequeno RNA não Traduzido/química , Pequeno RNA não Traduzido/classificação , Homologia de Sequência do Ácido Nucleico , Virulência/genética , Xanthomonas campestris/patogenicidadeRESUMO
BACKGROUND: In bacteria, small non-coding RNAs (sRNAs) have been recognized as important regulators of various cellular processes. Approximately 200 bacterial sRNAs in total have been reported. However, very few sRNAs have been identified from phytopathogenic bacteria. RESULTS: Xanthomons campestris pathovar campestris (Xcc) is the causal agent of black rot disease of cruciferous crops. In this study, a cDNA library was constructed from the low-molecular weight RNA isolated from the Xcc strain 8004 grown to exponential phase in the minimal medium XVM2. Seven sRNA candidates were obtained by sequencing screen of 2,500 clones from the library and four of them were confirmed to be sRNAs by Northern hybridization, which were named sRNA-Xcc1, sRNA-Xcc2, sRNA-Xcc3, and sRNA-Xcc4. The transcription start and stop sites of these sRNAs were further determined. BLAST analysis revealed that the four sRNAs are novel. Bioinformatics prediction showed that a large number of genes with various known or unknown functions in Xcc 8004 are potential targets of sRNA-Xcc1, sRNA-Xcc3 and sRNA-Xcc4. In contrast, only a few genes were predicted to be potential targets of sRNA-Xcc2. CONCLUSION: We have identified four novel sRNAs from Xcc by a large-scale screen. Bioinformatics analysis suggests that they may perform various functions. This work provides the first step toward understanding the role of sRNAs in the molecular mechanisms of Xanthomonas campestris pathogenesis.