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Characterisation of the mgo operon in Pseudomonas syringae pv. syringae UMAF0158 that is required for mangotoxin production

DOI: 10.1186/1471-2180-12-10

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Abstract:

In the present study, we performed a RT-PCR analysis, insertional inactivation mutagenesis, a promoter expression analysis and terminator localisation to study the gene cluster containing the mgoA gene. Additionally, we evaluated the importance of mgoC, mgoA and mgoD in mangotoxin production. A sequence analysis revealed an operon-like organisation. A promoter sequence was located upstream of the mgoB gene and was found to drive lacZ transcription. Two terminators were located downstream of the mgoD gene. RT-PCR experiments indicated that the four genes (mgoBCAD) constitute a transcriptional unit. This operon is similar in genetic organisation to those in the three other P. syringae pathovars for which complete genomes are available (P. syringae pv. syringae B728a, P. syringae pv. tomato DC3000 and P. syringae pv. phaseolicola 1448A). Interestingly, none of these three reference strains is capable of producing mangotoxin. Additionally, extract complementation resulted in a recovery of mangotoxin production when the defective mutant was complemented with wild-type extracts.The results of this study confirm that mgoB, mgoC, mgoA and mgoD function as a transcriptional unit and operon. While this operon is composed of four genes, only the last three are directly involved in mangotoxin production.Antimetabolite toxins are generally small metabolites that exhibit strong effects in plant cells by causing an increase in disease symptoms [1]. Various toxic substances produced by pathovars of Pseudomonas syringae have been well characterised. Each antimetabolite toxin inhibits a specific step in the glutamine and arginine biosynthesis pathways of the host, enhancing disease symptoms and increasing the virulence of the bacterial pathogen. The most well-studied antimetabolite toxins are tabtoxin and phaseolotoxin [2].Tabtoxin is a monocyclic β-lactam that specifically inhibits the enzyme glutamine synthetase (GS, EC 6.3.1.2). This toxin is produced by P. syringae pv. tabaci, pv

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